diff --git a/builtin.c b/builtin.c
index 3400c4976e..657143a739 100644
--- a/builtin.c
+++ b/builtin.c
@@ -50,17 +50,8 @@ load_with_builtin_functions(const char *feature_name, const struct rb_builtin_fu
     ASSUME(iseq); // otherwise an exception should have raised
     vm->builtin_function_table = NULL;
 
-    rb_namespace_enable_builtin();
-
     // exec
-    if (rb_namespace_available() && rb_mNamespaceRefiner) {
-        rb_iseq_eval_with_refinement(rb_iseq_check(iseq), rb_mNamespaceRefiner);
-    }
-    else {
-        rb_iseq_eval(rb_iseq_check(iseq));
-    }
-
-    rb_namespace_disable_builtin();
+    rb_iseq_eval(rb_iseq_check(iseq), rb_root_namespace()); // builtin functions are loaded in the root namespace
 }
 
 void
@@ -86,5 +77,11 @@ Init_builtin(void)
 void
 Init_builtin_features(void)
 {
+
+#ifdef BUILTIN_BINARY_SIZE
+
     load_with_builtin_functions("gem_prelude", NULL);
+
+#endif
+
 }
diff --git a/class.c b/class.c
index 24f61fd023..26486074f8 100644
--- a/class.c
+++ b/class.c
@@ -648,7 +648,7 @@ class_alloc0(enum ruby_value_type type, VALUE klass, bool namespaceable)
 {
     rb_ns_subclasses_t *ns_subclasses;
     rb_subclass_anchor_t *anchor;
-    const rb_namespace_t *ns = rb_definition_namespace();
+    const rb_namespace_t *ns = rb_current_namespace();
 
     if (!ruby_namespace_init_done) {
         namespaceable = true;
diff --git a/depend b/depend
index ea2486e9e8..95cb8afb22 100644
--- a/depend
+++ b/depend
@@ -9263,6 +9263,26 @@ namespace.$(OBJEXT): $(top_srcdir)/internal/string.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/variable.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/vm.h
 namespace.$(OBJEXT): $(top_srcdir)/internal/warnings.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/defines.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/encoding.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/node.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/options.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/pack.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/parser.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/prettyprint.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/prism.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/regexp.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/static_literals.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_buffer.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_char.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_constant_pool.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_integer.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_list.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_memchr.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_newline_list.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_string.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_strncasecmp.h
+namespace.$(OBJEXT): $(top_srcdir)/prism/util/pm_strpbrk.h
 namespace.$(OBJEXT): {$(VPATH)}assert.h
 namespace.$(OBJEXT): {$(VPATH)}atomic.h
 namespace.$(OBJEXT): {$(VPATH)}backward/2/assume.h
@@ -9279,6 +9299,7 @@ namespace.$(OBJEXT): {$(VPATH)}constant.h
 namespace.$(OBJEXT): {$(VPATH)}debug_counter.h
 namespace.$(OBJEXT): {$(VPATH)}defines.h
 namespace.$(OBJEXT): {$(VPATH)}encoding.h
+namespace.$(OBJEXT): {$(VPATH)}eval_intern.h
 namespace.$(OBJEXT): {$(VPATH)}id.h
 namespace.$(OBJEXT): {$(VPATH)}id_table.h
 namespace.$(OBJEXT): {$(VPATH)}intern.h
@@ -9433,12 +9454,17 @@ namespace.$(OBJEXT): {$(VPATH)}internal/value_type.h
 namespace.$(OBJEXT): {$(VPATH)}internal/variable.h
 namespace.$(OBJEXT): {$(VPATH)}internal/warning_push.h
 namespace.$(OBJEXT): {$(VPATH)}internal/xmalloc.h
+namespace.$(OBJEXT): {$(VPATH)}iseq.h
 namespace.$(OBJEXT): {$(VPATH)}method.h
 namespace.$(OBJEXT): {$(VPATH)}missing.h
 namespace.$(OBJEXT): {$(VPATH)}namespace.c
 namespace.$(OBJEXT): {$(VPATH)}node.h
 namespace.$(OBJEXT): {$(VPATH)}onigmo.h
 namespace.$(OBJEXT): {$(VPATH)}oniguruma.h
+namespace.$(OBJEXT): {$(VPATH)}prism/ast.h
+namespace.$(OBJEXT): {$(VPATH)}prism/diagnostic.h
+namespace.$(OBJEXT): {$(VPATH)}prism/version.h
+namespace.$(OBJEXT): {$(VPATH)}prism_compile.h
 namespace.$(OBJEXT): {$(VPATH)}ruby_assert.h
 namespace.$(OBJEXT): {$(VPATH)}ruby_atomic.h
 namespace.$(OBJEXT): {$(VPATH)}rubyparser.h
diff --git a/eval.c b/eval.c
index 019a2d19a2..0ff59efd98 100644
--- a/eval.c
+++ b/eval.c
@@ -80,6 +80,7 @@ ruby_setup(void)
     rb_vm_encoded_insn_data_table_init();
     Init_enable_namespace();
     Init_vm_objects();
+    Init_root_namespace();
     Init_fstring_table();
 
     EC_PUSH_TAG(GET_EC());
diff --git a/eval_intern.h b/eval_intern.h
index 2c244aa5e0..4ac950e238 100644
--- a/eval_intern.h
+++ b/eval_intern.h
@@ -296,7 +296,11 @@ VALUE rb_vm_make_jump_tag_but_local_jump(enum ruby_tag_type state, VALUE val);
 rb_cref_t *rb_vm_cref(void);
 rb_cref_t *rb_vm_cref_replace_with_duplicated_cref(void);
 VALUE rb_vm_call_cfunc(VALUE recv, VALUE (*func)(VALUE), VALUE arg, VALUE block_handler, VALUE filename);
-VALUE rb_vm_call_cfunc2(VALUE recv, VALUE (*func)(VALUE, VALUE), VALUE arg1, VALUE arg2, VALUE block_handler, VALUE filename);
+VALUE rb_vm_call_cfunc_in_namespace(VALUE recv, VALUE (*func)(VALUE, VALUE), VALUE arg1, VALUE arg2, VALUE filename, const rb_namespace_t *ns);
+void rb_vm_frame_flag_set_ns_require(const rb_execution_context_t *ec);
+const rb_namespace_t *rb_vm_current_namespace(const rb_execution_context_t *ec);
+const rb_namespace_t *rb_vm_caller_namespace(const rb_execution_context_t *ec);
+const rb_namespace_t *rb_vm_loading_namespace(const rb_execution_context_t *ec);
 void rb_vm_set_progname(VALUE filename);
 VALUE rb_vm_cbase(void);
 
diff --git a/inits.c b/inits.c
index e0dab9e890..5209e429f9 100644
--- a/inits.c
+++ b/inits.c
@@ -52,6 +52,7 @@ rb_call_inits(void)
     CALL(Time);
     CALL(Random);
     CALL(load);
+    CALL(Namespace);
     CALL(Proc);
     CALL(Binding);
     CALL(Math);
@@ -78,7 +79,6 @@ rb_call_inits(void)
     CALL(Prism);
     CALL(unicode_version);
     CALL(Set);
-    CALL(Namespace);
 
     // enable builtin loading
     CALL(builtin);
diff --git a/insns.def b/insns.def
index f21a1810a5..512e136abb 100644
--- a/insns.def
+++ b/insns.def
@@ -802,12 +802,13 @@ defineclass
 (VALUE val)
 {
     VALUE klass = vm_find_or_create_class_by_id(id, flags, cbase, super);
+    const rb_namespace_t *ns = rb_current_namespace();
 
     rb_iseq_check(class_iseq);
 
     /* enter scope */
     vm_push_frame(ec, class_iseq, VM_FRAME_MAGIC_CLASS | VM_ENV_FLAG_LOCAL, klass,
-                  GET_BLOCK_HANDLER(),
+                  GC_GUARDED_PTR(ns),
                   (VALUE)vm_cref_push(ec, klass, NULL, FALSE, FALSE),
                   ISEQ_BODY(class_iseq)->iseq_encoded, GET_SP(),
                   ISEQ_BODY(class_iseq)->local_table_size,
diff --git a/internal/class.h b/internal/class.h
index db4ae2ada1..adeb2c7854 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -390,8 +390,7 @@ RCLASS_EXT_READABLE_LOOKUP(VALUE obj, const rb_namespace_t *ns)
 static inline rb_classext_t *
 RCLASS_EXT_READABLE_IN_NS(VALUE obj, const rb_namespace_t *ns)
 {
-    if (!ns
-        || NAMESPACE_BUILTIN_P(ns)
+    if (NAMESPACE_ROOT_P(ns)
         || RCLASS_PRIME_CLASSEXT_READABLE_P(obj)) {
         return RCLASS_EXT_PRIME(obj);
     }
@@ -405,9 +404,9 @@ RCLASS_EXT_READABLE(VALUE obj)
     if (RCLASS_PRIME_CLASSEXT_READABLE_P(obj)) {
         return RCLASS_EXT_PRIME(obj);
     }
-    // delay namespace loading to optimize for unmodified classes
+    // delay determining the current namespace to optimize for unmodified classes
     ns = rb_current_namespace();
-    if (!ns || NAMESPACE_BUILTIN_P(ns)) {
+    if (NAMESPACE_ROOT_P(ns)) {
         return RCLASS_EXT_PRIME(obj);
     }
     return RCLASS_EXT_READABLE_LOOKUP(obj, ns);
@@ -440,8 +439,7 @@ RCLASS_EXT_WRITABLE_LOOKUP(VALUE obj, const rb_namespace_t *ns)
 static inline rb_classext_t *
 RCLASS_EXT_WRITABLE_IN_NS(VALUE obj, const rb_namespace_t *ns)
 {
-    if (!ns
-        || NAMESPACE_BUILTIN_P(ns)
+    if (NAMESPACE_ROOT_P(ns)
         || RCLASS_PRIME_CLASSEXT_WRITABLE_P(obj)) {
         return RCLASS_EXT_PRIME(obj);
     }
@@ -455,11 +453,9 @@ RCLASS_EXT_WRITABLE(VALUE obj)
     if (LIKELY(RCLASS_PRIME_CLASSEXT_WRITABLE_P(obj))) {
         return RCLASS_EXT_PRIME(obj);
     }
-    // delay namespace loading to optimize for unmodified classes
+    // delay determining the current namespace to optimize for unmodified classes
     ns = rb_current_namespace();
-    if (!ns || NAMESPACE_BUILTIN_P(ns)) {
-        // If no namespace is specified, Ruby VM is in bootstrap
-        // and the clean class definition is under construction.
+    if (NAMESPACE_ROOT_P(ns)) {
         return RCLASS_EXT_PRIME(obj);
     }
     return RCLASS_EXT_WRITABLE_LOOKUP(obj, ns);
diff --git a/internal/inits.h b/internal/inits.h
index e618d87cc3..c1cf3db94d 100644
--- a/internal/inits.h
+++ b/internal/inits.h
@@ -32,6 +32,9 @@ void Init_enable_namespace(void);
 void Init_BareVM(void);
 void Init_vm_objects(void);
 
+/* namespace.c */
+void Init_root_namespace(void);
+
 /* vm_backtrace.c */
 void Init_vm_backtrace(void);
 
diff --git a/internal/namespace.h b/internal/namespace.h
index 4cdfbc305f..9ffc9a5c8b 100644
--- a/internal/namespace.h
+++ b/internal/namespace.h
@@ -35,13 +35,14 @@ struct rb_namespace_struct {
 
     VALUE gvar_tbl;
 
-    bool is_builtin;
     bool is_user;
     bool is_optional;
 };
 typedef struct rb_namespace_struct rb_namespace_t;
 
-#define NAMESPACE_BUILTIN_P(ns) (ns && ns->is_builtin)
+#define NAMESPACE_OBJ_P(obj) (rb_obj_class(obj) == rb_cNamespace)
+
+#define NAMESPACE_ROOT_P(ns) (ns && !ns->is_user)
 #define NAMESPACE_USER_P(ns) (ns && ns->is_user)
 #define NAMESPACE_OPTIONAL_P(ns) (ns && ns->is_optional)
 #define NAMESPACE_MAIN_P(ns) (ns && ns->is_user && !ns->is_optional)
@@ -60,24 +61,16 @@ rb_namespace_available(void)
     return ruby_namespace_enabled;
 }
 
-void rb_namespace_enable_builtin(void);
-void rb_namespace_disable_builtin(void);
-void rb_namespace_push_loading_namespace(const rb_namespace_t *);
-void rb_namespace_pop_loading_namespace(const rb_namespace_t *);
-rb_namespace_t * rb_root_namespace(void);
-const rb_namespace_t *rb_builtin_namespace(void);
-rb_namespace_t * rb_main_namespace(void);
-const rb_namespace_t * rb_definition_namespace(void);
-const rb_namespace_t * rb_loading_namespace(void);
+const rb_namespace_t * rb_root_namespace(void);
+const rb_namespace_t * rb_main_namespace(void);
 const rb_namespace_t * rb_current_namespace(void);
-VALUE rb_current_namespace_details(VALUE);
+const rb_namespace_t * rb_loading_namespace(void);
 
 void rb_namespace_entry_mark(void *);
+void rb_namespace_gc_update_references(void *ptr);
 
 rb_namespace_t * rb_get_namespace_t(VALUE ns);
 VALUE rb_get_namespace_object(rb_namespace_t *ns);
-typedef VALUE namespace_exec_func(VALUE arg);
-VALUE rb_namespace_exec(const rb_namespace_t *ns, namespace_exec_func *func, VALUE arg);
 
 VALUE rb_namespace_local_extension(VALUE namespace, VALUE fname, VALUE path);
 
diff --git a/iseq.c b/iseq.c
index 4334bdd795..dad721f2ac 100644
--- a/iseq.c
+++ b/iseq.c
@@ -1143,6 +1143,21 @@ rb_iseq_load_iseq(VALUE fname)
     return NULL;
 }
 
+const rb_iseq_t *
+rb_iseq_compile_iseq(VALUE str, VALUE fname)
+{
+    VALUE args[] = {
+        str, fname
+    };
+    VALUE iseqv = rb_check_funcall(rb_cISeq, rb_intern("compile"), 2, args);
+
+    if (!SPECIAL_CONST_P(iseqv) && RBASIC_CLASS(iseqv) == rb_cISeq) {
+        return iseqw_check(iseqv);
+    }
+
+    return NULL;
+}
+
 #define CHECK_ARRAY(v)   rb_to_array_type(v)
 #define CHECK_HASH(v)    rb_to_hash_type(v)
 #define CHECK_STRING(v)  rb_str_to_str(v)
@@ -1955,7 +1970,7 @@ iseqw_eval(VALUE self)
     if (0 == ISEQ_BODY(iseq)->iseq_size) {
         rb_raise(rb_eTypeError, "attempt to evaluate dummy InstructionSequence");
     }
-    return rb_iseq_eval(iseq);
+    return rb_iseq_eval(iseq, rb_current_namespace());
 }
 
 /*
diff --git a/iseq.h b/iseq.h
index 1cecc6960d..b814a0c1e3 100644
--- a/iseq.h
+++ b/iseq.h
@@ -187,6 +187,7 @@ void rb_iseq_init_trace(rb_iseq_t *iseq);
 int rb_iseq_add_local_tracepoint_recursively(const rb_iseq_t *iseq, rb_event_flag_t turnon_events, VALUE tpval, unsigned int target_line, bool target_bmethod);
 int rb_iseq_remove_local_tracepoint_recursively(const rb_iseq_t *iseq, VALUE tpval);
 const rb_iseq_t *rb_iseq_load_iseq(VALUE fname);
+const rb_iseq_t *rb_iseq_compile_iseq(VALUE str, VALUE fname);
 int rb_iseq_opt_frozen_string_literal(void);
 
 #if VM_INSN_INFO_TABLE_IMPL == 2
diff --git a/load.c b/load.c
index b85a247c18..8a9c31961c 100644
--- a/load.c
+++ b/load.c
@@ -23,8 +23,6 @@
 #include "ractor_core.h"
 #include "vm_core.h"
 
-static VALUE ruby_dln_libmap;
-
 #define IS_RBEXT(e) (strcmp((e), ".rb") == 0)
 #define IS_SOEXT(e) (strcmp((e), ".so") == 0 || strcmp((e), ".o") == 0)
 #define IS_DLEXT(e) (strcmp((e), DLEXT) == 0)
@@ -39,38 +37,6 @@ static VALUE ruby_dln_libmap;
 # error Need integer for VALUE
 #endif
 
-#define IS_NAMESPACE(obj) (CLASS_OF(obj) == rb_cNamespace)
-
-struct vm_and_namespace_struct {
-    rb_vm_t *vm;
-    rb_namespace_t *ns;
-};
-typedef struct vm_and_namespace_struct vm_ns_t;
-#define GET_vm_ns() vm_ns_t vm_ns_v = { .vm = GET_VM(), .ns = (rb_namespace_t *)rb_current_namespace(), }; vm_ns_t *vm_ns = &vm_ns_v;
-#define GET_loading_vm_ns() vm_ns_t vm_ns_v = { .vm = GET_VM(), .ns = (rb_namespace_t *)rb_loading_namespace(), }; vm_ns_t *vm_ns = &vm_ns_v;
-
-#define CURRENT_NS_attr(vm_ns, attr) (NAMESPACE_USER_P(vm_ns->ns) ? vm_ns->ns->attr : vm_ns->vm->attr)
-#define SET_NS_attr(vm_ns, attr, value) do {                      \
-    if (NAMESPACE_USER_P(vm_ns->ns)) { vm_ns->ns->attr = value; } \
-    else { vm_ns->vm->attr = value; }                             \
-} while (0)
-
-#define SET_NS_LOAD_PATH_CHECK_CACHE(vm_ns, value) SET_NS_attr(vm_ns, load_path_check_cache, value)
-#define SET_NS_EXPANDED_LOAD_PATH(vm_ns, value)    SET_NS_attr(vm_ns, expanded_load_path, value)
-
-#define CURRENT_NS_LOAD_PATH(vm_ns)             CURRENT_NS_attr(vm_ns, load_path)
-#define CURRENT_NS_LOAD_PATH_SNAPSHOT(vm_ns)    CURRENT_NS_attr(vm_ns, load_path_snapshot)
-#define CURRENT_NS_LOAD_PATH_CHECK_CACHE(vm_ns) CURRENT_NS_attr(vm_ns, load_path_check_cache)
-#define CURRENT_NS_EXPANDED_LOAD_PATH(vm_ns)    CURRENT_NS_attr(vm_ns, expanded_load_path)
-#define CURRENT_NS_LOADING_TABLE(vm_ns)         CURRENT_NS_attr(vm_ns, loading_table)
-#define CURRENT_NS_LOADED_FEATURES(vm_ns)       CURRENT_NS_attr(vm_ns, loaded_features)
-#define CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns)     CURRENT_NS_attr(vm_ns, loaded_features_snapshot)
-#define CURRENT_NS_LOADED_FEATURES_REALPATHS(vm_ns)    CURRENT_NS_attr(vm_ns, loaded_features_realpaths)
-#define CURRENT_NS_LOADED_FEATURES_REALPATH_MAP(vm_ns) CURRENT_NS_attr(vm_ns, loaded_features_realpath_map)
-#define CURRENT_NS_LOADED_FEATURES_INDEX(vm_ns)        CURRENT_NS_attr(vm_ns, loaded_features_index)
-
-#define CURRENT_NS_RUBY_DLN_LIBMAP(vm_ns, map) (NAMESPACE_USER_P(vm_ns->ns) ? vm_ns->ns->ruby_dln_libmap : map)
-
 enum {
     loadable_ext_rb = (0+ /* .rb extension is the first in both tables */
                        1) /* offset by rb_find_file_ext() */
@@ -99,10 +65,10 @@ enum expand_type {
    string objects in $LOAD_PATH are frozen.
  */
 static void
-rb_construct_expanded_load_path(vm_ns_t *vm_ns, enum expand_type type, int *has_relative, int *has_non_cache)
+rb_construct_expanded_load_path(rb_namespace_t *ns, enum expand_type type, int *has_relative, int *has_non_cache)
 {
-    VALUE load_path = CURRENT_NS_LOAD_PATH(vm_ns);
-    VALUE expanded_load_path = CURRENT_NS_EXPANDED_LOAD_PATH(vm_ns);
+    VALUE load_path = ns->load_path;
+    VALUE expanded_load_path = ns->expanded_load_path;
     VALUE snapshot;
     VALUE ary;
     long i;
@@ -142,39 +108,39 @@ rb_construct_expanded_load_path(vm_ns_t *vm_ns, enum expand_type type, int *has_
         rb_ary_push(ary, rb_fstring(expanded_path));
     }
     rb_ary_freeze(ary);
-    SET_NS_EXPANDED_LOAD_PATH(vm_ns, ary);
-    snapshot = CURRENT_NS_LOAD_PATH_SNAPSHOT(vm_ns);
-    load_path = CURRENT_NS_LOAD_PATH(vm_ns);
+    ns->expanded_load_path = ary;
+    snapshot = ns->load_path_snapshot;
+    load_path = ns->load_path;
     rb_ary_replace(snapshot, load_path);
 }
 
 static VALUE
-get_expanded_load_path(vm_ns_t *vm_ns)
+get_expanded_load_path(rb_namespace_t *ns)
 {
     VALUE check_cache;
     const VALUE non_cache = Qtrue;
-    const VALUE load_path_snapshot = CURRENT_NS_LOAD_PATH_SNAPSHOT(vm_ns);
-    const VALUE load_path = CURRENT_NS_LOAD_PATH(vm_ns);
+    const VALUE load_path_snapshot = ns->load_path_snapshot;
+    const VALUE load_path = ns->load_path;
 
     if (!rb_ary_shared_with_p(load_path_snapshot, load_path)) {
         /* The load path was modified. Rebuild the expanded load path. */
         int has_relative = 0, has_non_cache = 0;
-        rb_construct_expanded_load_path(vm_ns, EXPAND_ALL, &has_relative, &has_non_cache);
+        rb_construct_expanded_load_path(ns, EXPAND_ALL, &has_relative, &has_non_cache);
         if (has_relative) {
-            SET_NS_LOAD_PATH_CHECK_CACHE(vm_ns, rb_dir_getwd_ospath());
+            ns->load_path_check_cache = rb_dir_getwd_ospath();
         }
         else if (has_non_cache) {
             /* Non string object. */
-            SET_NS_LOAD_PATH_CHECK_CACHE(vm_ns, non_cache);
+            ns->load_path_check_cache = non_cache;
         }
         else {
-            SET_NS_LOAD_PATH_CHECK_CACHE(vm_ns, 0);
+            ns->load_path_check_cache = 0;
         }
     }
-    else if ((check_cache = CURRENT_NS_LOAD_PATH_CHECK_CACHE(vm_ns)) == non_cache) {
+    else if ((check_cache = ns->load_path_check_cache) == non_cache) {
         int has_relative = 1, has_non_cache = 1;
         /* Expand only non-cacheable objects. */
-        rb_construct_expanded_load_path(vm_ns, EXPAND_NON_CACHE,
+        rb_construct_expanded_load_path(ns, EXPAND_NON_CACHE,
                                         &has_relative, &has_non_cache);
     }
     else if (check_cache) {
@@ -183,76 +149,49 @@ get_expanded_load_path(vm_ns_t *vm_ns)
         if (!rb_str_equal(check_cache, cwd)) {
             /* Current working directory or filesystem encoding was changed.
                Expand relative load path and non-cacheable objects again. */
-            SET_NS_LOAD_PATH_CHECK_CACHE(vm_ns, cwd);
-            rb_construct_expanded_load_path(vm_ns, EXPAND_RELATIVE,
+            ns->load_path_check_cache = cwd;
+            rb_construct_expanded_load_path(ns, EXPAND_RELATIVE,
                                             &has_relative, &has_non_cache);
         }
         else {
             /* Expand only tilde (User HOME) and non-cacheable objects. */
-            rb_construct_expanded_load_path(vm_ns, EXPAND_HOME,
+            rb_construct_expanded_load_path(ns, EXPAND_HOME,
                                             &has_relative, &has_non_cache);
         }
     }
-    return CURRENT_NS_EXPANDED_LOAD_PATH(vm_ns);
+    return ns->expanded_load_path;
 }
 
 VALUE
 rb_get_expanded_load_path(void)
 {
-    GET_loading_vm_ns();
-    return get_expanded_load_path(vm_ns);
+    return get_expanded_load_path((rb_namespace_t *)rb_loading_namespace());
 }
 
 static VALUE
-load_path_getter(ID id, VALUE * p)
+load_path_getter(ID _x, VALUE * _y)
 {
-    GET_loading_vm_ns();
-    return CURRENT_NS_LOAD_PATH(vm_ns);
-}
-
-static VALUE
-get_loaded_features(vm_ns_t *vm_ns)
-{
-    return CURRENT_NS_LOADED_FEATURES(vm_ns);
-}
-
-static VALUE
-get_loaded_features_realpaths(vm_ns_t *vm_ns)
-{
-    return CURRENT_NS_LOADED_FEATURES_REALPATHS(vm_ns);
-}
-
-static VALUE
-get_loaded_features_realpath_map(vm_ns_t *vm_ns)
-{
-    return CURRENT_NS_LOADED_FEATURES_REALPATH_MAP(vm_ns);
+    return rb_loading_namespace()->load_path;
 }
 
 static VALUE
 get_LOADED_FEATURES(ID _x, VALUE *_y)
 {
-    GET_loading_vm_ns();
-    return get_loaded_features(vm_ns);
+    return rb_loading_namespace()->loaded_features;
 }
 
 static void
-reset_loaded_features_snapshot(vm_ns_t *vm_ns)
+reset_loaded_features_snapshot(const rb_namespace_t *ns)
 {
-    VALUE snapshot = CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns);
-    VALUE loaded_features = CURRENT_NS_LOADED_FEATURES(vm_ns);
+    VALUE snapshot = ns->loaded_features_snapshot;
+    VALUE loaded_features = ns->loaded_features;
     rb_ary_replace(snapshot, loaded_features);
 }
 
 static struct st_table *
-get_loaded_features_index_raw(vm_ns_t *vm_ns)
+get_loaded_features_index_raw(const rb_namespace_t *ns)
 {
-    return CURRENT_NS_LOADED_FEATURES_INDEX(vm_ns);
-}
-
-static st_table *
-get_loading_table(vm_ns_t *vm_ns)
-{
-    return CURRENT_NS_LOADING_TABLE(vm_ns);
+    return ns->loaded_features_index;
 }
 
 static st_data_t
@@ -273,7 +212,7 @@ is_rbext_path(VALUE feature_path)
 typedef rb_darray(long) feature_indexes_t;
 
 struct features_index_add_single_args {
-    vm_ns_t *vm_ns;
+    const rb_namespace_t *ns;
     VALUE offset;
     bool rb;
 };
@@ -282,7 +221,7 @@ static int
 features_index_add_single_callback(st_data_t *key, st_data_t *value, st_data_t raw_args, int existing)
 {
     struct features_index_add_single_args *args = (struct features_index_add_single_args *)raw_args;
-    vm_ns_t *vm_ns = args->vm_ns;
+    const rb_namespace_t *ns = args->ns;
     VALUE offset = args->offset;
     bool rb = args->rb;
 
@@ -290,7 +229,7 @@ features_index_add_single_callback(st_data_t *key, st_data_t *value, st_data_t r
         VALUE this_feature_index = *value;
 
         if (FIXNUM_P(this_feature_index)) {
-            VALUE loaded_features = get_loaded_features(vm_ns);
+            VALUE loaded_features = ns->loaded_features;
             VALUE this_feature_path = RARRAY_AREF(loaded_features, FIX2LONG(this_feature_index));
 
             feature_indexes_t feature_indexes;
@@ -310,7 +249,7 @@ features_index_add_single_callback(st_data_t *key, st_data_t *value, st_data_t r
             long pos = -1;
 
             if (rb) {
-                VALUE loaded_features = get_loaded_features(vm_ns);
+                VALUE loaded_features = ns->loaded_features;
                 for (size_t i = 0; i < rb_darray_size(feature_indexes); ++i) {
                     long idx = rb_darray_get(feature_indexes, i);
                     VALUE this_feature_path = RARRAY_AREF(loaded_features, idx);
@@ -342,7 +281,7 @@ features_index_add_single_callback(st_data_t *key, st_data_t *value, st_data_t r
 }
 
 static void
-features_index_add_single(vm_ns_t *vm_ns, const char* str, size_t len, VALUE offset, bool rb)
+features_index_add_single(const rb_namespace_t *ns, const char* str, size_t len, VALUE offset, bool rb)
 {
     struct st_table *features_index;
     st_data_t short_feature_key;
@@ -350,10 +289,10 @@ features_index_add_single(vm_ns_t *vm_ns, const char* str, size_t len, VALUE off
     Check_Type(offset, T_FIXNUM);
     short_feature_key = feature_key(str, len);
 
-    features_index = get_loaded_features_index_raw(vm_ns);
+    features_index = get_loaded_features_index_raw(ns);
 
     struct features_index_add_single_args args = {
-        .vm_ns = vm_ns,
+        .ns = ns,
         .offset = offset,
         .rb = rb,
     };
@@ -370,7 +309,7 @@ features_index_add_single(vm_ns_t *vm_ns, const char* str, size_t len, VALUE off
    relies on for its fast lookup.
 */
 static void
-features_index_add(vm_ns_t *vm_ns, VALUE feature, VALUE offset)
+features_index_add(const rb_namespace_t *ns, VALUE feature, VALUE offset)
 {
     RUBY_ASSERT(rb_ractor_main_p());
 
@@ -398,14 +337,14 @@ features_index_add(vm_ns_t *vm_ns, VALUE feature, VALUE offset)
         if (p < feature_str)
             break;
         /* Now *p == '/'.  We reach this point for every '/' in `feature`. */
-        features_index_add_single(vm_ns, p + 1, feature_end - p - 1, offset, false);
+        features_index_add_single(ns, p + 1, feature_end - p - 1, offset, false);
         if (ext) {
-            features_index_add_single(vm_ns, p + 1, ext - p - 1, offset, rb);
+            features_index_add_single(ns, p + 1, ext - p - 1, offset, rb);
         }
     }
-    features_index_add_single(vm_ns, feature_str, feature_end - feature_str, offset, false);
+    features_index_add_single(ns, feature_str, feature_end - feature_str, offset, false);
     if (ext) {
-        features_index_add_single(vm_ns, feature_str, ext - feature_str, offset, rb);
+        features_index_add_single(ns, feature_str, ext - feature_str, offset, rb);
     }
 }
 
@@ -419,31 +358,20 @@ loaded_features_index_clear_i(st_data_t key, st_data_t val, st_data_t arg)
     return ST_DELETE;
 }
 
-void
-rb_free_loaded_features_index(rb_vm_t *vm)
-{
-    /* Destructs vm->loaded_features_index directly because this is only for
-       the VM destruction */
-    st_foreach(vm->loaded_features_index, loaded_features_index_clear_i, 0);
-    st_free_table(vm->loaded_features_index);
-}
-
-
-
 static st_table *
-get_loaded_features_index(vm_ns_t *vm_ns)
+get_loaded_features_index(const rb_namespace_t *ns)
 {
     int i;
-    VALUE features = CURRENT_NS_LOADED_FEATURES(vm_ns);
-    const VALUE snapshot = CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns);
+    VALUE features = ns->loaded_features;
+    const VALUE snapshot = ns->loaded_features_snapshot;
 
     if (!rb_ary_shared_with_p(snapshot, features)) {
         /* The sharing was broken; something (other than us in rb_provide_feature())
            modified loaded_features.  Rebuild the index. */
-        st_foreach(CURRENT_NS_LOADED_FEATURES_INDEX(vm_ns), loaded_features_index_clear_i, 0);
+        st_foreach(ns->loaded_features_index, loaded_features_index_clear_i, 0);
 
-        VALUE realpaths = CURRENT_NS_LOADED_FEATURES_REALPATHS(vm_ns);
-        VALUE realpath_map = CURRENT_NS_LOADED_FEATURES_REALPATH_MAP(vm_ns);
+        VALUE realpaths = ns->loaded_features_realpaths;
+        VALUE realpath_map = ns->loaded_features_realpath_map;
         VALUE previous_realpath_map = rb_hash_dup(realpath_map);
         rb_hash_clear(realpaths);
         rb_hash_clear(realpath_map);
@@ -454,11 +382,11 @@ get_loaded_features_index(vm_ns_t *vm_ns)
             as_str = rb_fstring(as_str);
             if (as_str != entry)
                 rb_ary_store(features, i, as_str);
-            features_index_add(vm_ns, as_str, INT2FIX(i));
+            features_index_add(ns, as_str, INT2FIX(i));
         }
-        reset_loaded_features_snapshot(vm_ns);
+        reset_loaded_features_snapshot(ns);
 
-        features = CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns);
+        features = ns->loaded_features_snapshot;
         long j = RARRAY_LEN(features);
         for (i = 0; i < j; i++) {
             VALUE as_str = rb_ary_entry(features, i);
@@ -472,7 +400,7 @@ get_loaded_features_index(vm_ns_t *vm_ns)
             rb_hash_aset(realpath_map, as_str, realpath);
         }
     }
-    return CURRENT_NS_LOADED_FEATURES_INDEX(vm_ns);
+    return ns->loaded_features_index;
 }
 
 /* This searches `load_path` for a value such that
@@ -557,7 +485,7 @@ loaded_feature_path_i(st_data_t v, st_data_t b, st_data_t f)
  * 'u': unsuffixed
  */
 static int
-rb_feature_p(vm_ns_t *vm_ns, const char *feature, const char *ext, int rb, int expanded, const char **fn)
+rb_feature_p(const rb_namespace_t *ns, const char *feature, const char *ext, int rb, int expanded, const char **fn)
 {
     VALUE features, this_feature_index = Qnil, v, p, load_path = 0;
     const char *f, *e;
@@ -578,8 +506,8 @@ rb_feature_p(vm_ns_t *vm_ns, const char *feature, const char *ext, int rb, int e
         elen = 0;
         type = 0;
     }
-    features = get_loaded_features(vm_ns);
-    features_index = get_loaded_features_index(vm_ns);
+    features = ns->loaded_features;
+    features_index = get_loaded_features_index(ns);
 
     key = feature_key(feature, strlen(feature));
     /* We search `features` for an entry such that either
@@ -626,7 +554,7 @@ rb_feature_p(vm_ns_t *vm_ns, const char *feature, const char *ext, int rb, int e
             if ((n = RSTRING_LEN(v)) < len) continue;
             if (strncmp(f, feature, len) != 0) {
                 if (expanded) continue;
-                if (!load_path) load_path = get_expanded_load_path(vm_ns);
+                if (!load_path) load_path = get_expanded_load_path((rb_namespace_t *)ns);
                 if (!(p = loaded_feature_path(f, n, feature, len, type, load_path)))
                     continue;
                 expanded = 1;
@@ -646,14 +574,14 @@ rb_feature_p(vm_ns_t *vm_ns, const char *feature, const char *ext, int rb, int e
         }
     }
 
-    loading_tbl = get_loading_table(vm_ns);
+    loading_tbl = ns->loading_table;
     f = 0;
     if (!expanded && !rb_is_absolute_path(feature)) {
         struct loaded_feature_searching fs;
         fs.name = feature;
         fs.len = len;
         fs.type = type;
-        fs.load_path = load_path ? load_path : get_expanded_load_path(vm_ns);
+        fs.load_path = load_path ? load_path : get_expanded_load_path((rb_namespace_t *)ns);
         fs.result = 0;
         st_foreach(loading_tbl, loaded_feature_path_i, (st_data_t)&fs);
         if ((f = fs.result) != 0) {
@@ -708,7 +636,7 @@ rb_provided(const char *feature)
 }
 
 static int
-feature_provided(vm_ns_t *vm_ns, const char *feature, const char **loading)
+feature_provided(rb_namespace_t *ns, const char *feature, const char **loading)
 {
     const char *ext = strrchr(feature, '.');
     VALUE fullpath = 0;
@@ -720,15 +648,15 @@ feature_provided(vm_ns_t *vm_ns, const char *feature, const char **loading)
     }
     if (ext && !strchr(ext, '/')) {
         if (IS_RBEXT(ext)) {
-            if (rb_feature_p(vm_ns, feature, ext, TRUE, FALSE, loading)) return TRUE;
+            if (rb_feature_p(ns, feature, ext, TRUE, FALSE, loading)) return TRUE;
             return FALSE;
         }
         else if (IS_SOEXT(ext) || IS_DLEXT(ext)) {
-            if (rb_feature_p(vm_ns, feature, ext, FALSE, FALSE, loading)) return TRUE;
+            if (rb_feature_p(ns, feature, ext, FALSE, FALSE, loading)) return TRUE;
             return FALSE;
         }
     }
-    if (rb_feature_p(vm_ns, feature, 0, TRUE, FALSE, loading))
+    if (rb_feature_p(ns, feature, 0, TRUE, FALSE, loading))
         return TRUE;
     RB_GC_GUARD(fullpath);
     return FALSE;
@@ -737,30 +665,30 @@ feature_provided(vm_ns_t *vm_ns, const char *feature, const char **loading)
 int
 rb_feature_provided(const char *feature, const char **loading)
 {
-    GET_vm_ns();
-    return feature_provided(vm_ns, feature, loading);
+    rb_namespace_t *ns = (rb_namespace_t *)rb_current_namespace();
+    return feature_provided(ns, feature, loading);
 }
 
 static void
-rb_provide_feature(vm_ns_t *vm_ns, VALUE feature)
+rb_provide_feature(const rb_namespace_t *ns, VALUE feature)
 {
     VALUE features;
 
-    features = get_loaded_features(vm_ns);
+    features = ns->loaded_features;
     if (OBJ_FROZEN(features)) {
         rb_raise(rb_eRuntimeError,
                  "$LOADED_FEATURES is frozen; cannot append feature");
     }
     feature = rb_fstring(feature);
 
-    get_loaded_features_index(vm_ns);
+    get_loaded_features_index(ns);
     // If loaded_features and loaded_features_snapshot share the same backing
     // array, pushing into it would cause the whole array to be copied.
     // To avoid this we first clear loaded_features_snapshot.
-    rb_ary_clear(CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns));
+    rb_ary_clear(ns->loaded_features_snapshot);
     rb_ary_push(features, feature);
-    features_index_add(vm_ns, feature, INT2FIX(RARRAY_LEN(features)-1));
-    reset_loaded_features_snapshot(vm_ns);
+    features_index_add(ns, feature, INT2FIX(RARRAY_LEN(features)-1));
+    reset_loaded_features_snapshot(ns);
 }
 
 void
@@ -770,8 +698,7 @@ rb_provide(const char *feature)
      * rb_provide() must use rb_current_namespace to store provided features
      * in the current namespace's loaded_features, etc.
      */
-    GET_vm_ns();
-    rb_provide_feature(vm_ns, rb_fstring_cstr(feature));
+    rb_provide_feature(rb_current_namespace(), rb_fstring_cstr(feature));
 }
 
 NORETURN(static void load_failed(VALUE));
@@ -789,35 +716,17 @@ realpath_internal_cached(VALUE hash, VALUE path)
     return realpath;
 }
 
-struct iseq_eval_in_namespace_data {
-    const rb_iseq_t *iseq;
-    bool in_builtin;
-};
-
-static VALUE
-iseq_eval_in_namespace(VALUE arg)
-{
-    struct iseq_eval_in_namespace_data *data = (struct iseq_eval_in_namespace_data *)arg;
-    if (rb_namespace_available() && data->in_builtin) {
-        return rb_iseq_eval_with_refinement(data->iseq, rb_mNamespaceRefiner);
-    }
-    else {
-        return rb_iseq_eval(data->iseq);
-    }
-}
-
 static inline void
 load_iseq_eval(rb_execution_context_t *ec, VALUE fname)
 {
-    GET_loading_vm_ns();
-    const rb_namespace_t *loading_ns = rb_loading_namespace();
+    const rb_namespace_t *ns = rb_loading_namespace();
     const rb_iseq_t *iseq = rb_iseq_load_iseq(fname);
 
     if (!iseq) {
         rb_execution_context_t *ec = GET_EC();
         VALUE v = rb_vm_push_frame_fname(ec, fname);
 
-        VALUE realpath_map = get_loaded_features_realpath_map(vm_ns);
+        VALUE realpath_map = ns->loaded_features_realpath_map;
 
         if (rb_ruby_prism_p()) {
             pm_parse_result_t result = { 0 };
@@ -862,16 +771,7 @@ load_iseq_eval(rb_execution_context_t *ec, VALUE fname)
     }
     rb_exec_event_hook_script_compiled(ec, iseq, Qnil);
 
-    if (loading_ns) {
-        struct iseq_eval_in_namespace_data arg = {
-            .iseq = iseq,
-            .in_builtin = NAMESPACE_BUILTIN_P(loading_ns),
-        };
-        rb_namespace_exec(loading_ns, iseq_eval_in_namespace, (VALUE)&arg);
-    }
-    else {
-        rb_iseq_eval(iseq);
-    }
+    rb_iseq_eval(iseq, ns);
 }
 
 static inline enum ruby_tag_type
@@ -889,7 +789,7 @@ load_wrapping(rb_execution_context_t *ec, VALUE fname, VALUE load_wrapper)
     ec->errinfo = Qnil; /* ensure */
 
     /* load in module as toplevel */
-    if (IS_NAMESPACE(load_wrapper)) {
+    if (NAMESPACE_OBJ_P(load_wrapper)) {
         ns = rb_get_namespace_t(load_wrapper);
         if (!ns->top_self) {
             ns->top_self = rb_obj_clone(rb_vm_top_self());
@@ -1048,10 +948,10 @@ rb_f_load(int argc, VALUE *argv, VALUE _)
 }
 
 static char *
-load_lock(vm_ns_t *vm_ns, const char *ftptr, bool warn)
+load_lock(const rb_namespace_t *ns, const char *ftptr, bool warn)
 {
     st_data_t data;
-    st_table *loading_tbl = get_loading_table(vm_ns);
+    st_table *loading_tbl = ns->loading_table;
 
     if (!st_lookup(loading_tbl, (st_data_t)ftptr, &data)) {
         /* partial state */
@@ -1093,11 +993,11 @@ release_thread_shield(st_data_t *key, st_data_t *value, st_data_t done, int exis
 }
 
 static void
-load_unlock(vm_ns_t *vm_ns, const char *ftptr, int done)
+load_unlock(const rb_namespace_t *ns, const char *ftptr, int done)
 {
     if (ftptr) {
         st_data_t key = (st_data_t)ftptr;
-        st_table *loading_tbl = get_loading_table(vm_ns);
+        st_table *loading_tbl = ns->loading_table;
 
         st_update(loading_tbl, key, release_thread_shield, done);
     }
@@ -1176,10 +1076,10 @@ rb_f_require_relative(VALUE obj, VALUE fname)
     return rb_require_relative_entrypoint(fname);
 }
 
-typedef int (*feature_func)(vm_ns_t *vm_ns, const char *feature, const char *ext, int rb, int expanded, const char **fn);
+typedef int (*feature_func)(const rb_namespace_t *ns, const char *feature, const char *ext, int rb, int expanded, const char **fn);
 
 static int
-search_required(vm_ns_t *vm_ns, VALUE fname, volatile VALUE *path, feature_func rb_feature_p)
+search_required(const rb_namespace_t *ns, VALUE fname, volatile VALUE *path, feature_func rb_feature_p)
 {
     VALUE tmp;
     char *ext, *ftptr;
@@ -1190,20 +1090,20 @@ search_required(vm_ns_t *vm_ns, VALUE fname, volatile VALUE *path, feature_func
     ext = strrchr(ftptr = RSTRING_PTR(fname), '.');
     if (ext && !strchr(ext, '/')) {
         if (IS_RBEXT(ext)) {
-            if (rb_feature_p(vm_ns, ftptr, ext, TRUE, FALSE, &loading)) {
+            if (rb_feature_p(ns, ftptr, ext, TRUE, FALSE, &loading)) {
                 if (loading) *path = rb_filesystem_str_new_cstr(loading);
                 return 'r';
             }
             if ((tmp = rb_find_file(fname)) != 0) {
                 ext = strrchr(ftptr = RSTRING_PTR(tmp), '.');
-                if (!rb_feature_p(vm_ns, ftptr, ext, TRUE, TRUE, &loading) || loading)
+                if (!rb_feature_p(ns, ftptr, ext, TRUE, TRUE, &loading) || loading)
                     *path = tmp;
                 return 'r';
             }
             return 0;
         }
         else if (IS_SOEXT(ext)) {
-            if (rb_feature_p(vm_ns, ftptr, ext, FALSE, FALSE, &loading)) {
+            if (rb_feature_p(ns, ftptr, ext, FALSE, FALSE, &loading)) {
                 if (loading) *path = rb_filesystem_str_new_cstr(loading);
                 return 's';
             }
@@ -1212,25 +1112,25 @@ search_required(vm_ns_t *vm_ns, VALUE fname, volatile VALUE *path, feature_func
             OBJ_FREEZE(tmp);
             if ((tmp = rb_find_file(tmp)) != 0) {
                 ext = strrchr(ftptr = RSTRING_PTR(tmp), '.');
-                if (!rb_feature_p(vm_ns, ftptr, ext, FALSE, TRUE, &loading) || loading)
+                if (!rb_feature_p(ns, ftptr, ext, FALSE, TRUE, &loading) || loading)
                     *path = tmp;
                 return 's';
             }
         }
         else if (IS_DLEXT(ext)) {
-            if (rb_feature_p(vm_ns, ftptr, ext, FALSE, FALSE, &loading)) {
+            if (rb_feature_p(ns, ftptr, ext, FALSE, FALSE, &loading)) {
                 if (loading) *path = rb_filesystem_str_new_cstr(loading);
                 return 's';
             }
             if ((tmp = rb_find_file(fname)) != 0) {
                 ext = strrchr(ftptr = RSTRING_PTR(tmp), '.');
-                if (!rb_feature_p(vm_ns, ftptr, ext, FALSE, TRUE, &loading) || loading)
+                if (!rb_feature_p(ns, ftptr, ext, FALSE, TRUE, &loading) || loading)
                     *path = tmp;
                 return 's';
             }
         }
     }
-    else if ((ft = rb_feature_p(vm_ns, ftptr, 0, FALSE, FALSE, &loading)) == 'r') {
+    else if ((ft = rb_feature_p(ns, ftptr, 0, FALSE, FALSE, &loading)) == 'r') {
         if (loading) *path = rb_filesystem_str_new_cstr(loading);
         return 'r';
     }
@@ -1239,20 +1139,23 @@ search_required(vm_ns_t *vm_ns, VALUE fname, volatile VALUE *path, feature_func
 
     // Check if it's a statically linked extension when
     // not already a feature and not found as a dynamic library.
-    if (!ft && type != loadable_ext_rb && vm_ns->vm->static_ext_inits) {
-        VALUE lookup_name = tmp;
-        // Append ".so" if not already present so for example "etc" can find "etc.so".
-        // We always register statically linked extensions with a ".so" extension.
-        // See encinit.c and extinit.c (generated at build-time).
-        if (!ext) {
-            lookup_name = rb_str_dup(lookup_name);
-            rb_str_cat_cstr(lookup_name, ".so");
-        }
-        ftptr = RSTRING_PTR(lookup_name);
-        if (st_lookup(vm_ns->vm->static_ext_inits, (st_data_t)ftptr, NULL)) {
-            *path = rb_filesystem_str_new_cstr(ftptr);
-            RB_GC_GUARD(lookup_name);
-            return 's';
+    if (!ft && type != loadable_ext_rb) {
+        rb_vm_t *vm = GET_VM();
+        if (vm->static_ext_inits) {
+            VALUE lookup_name = tmp;
+            // Append ".so" if not already present so for example "etc" can find "etc.so".
+            // We always register statically linked extensions with a ".so" extension.
+            // See encinit.c and extinit.c (generated at build-time).
+            if (!ext) {
+                lookup_name = rb_str_dup(lookup_name);
+                rb_str_cat_cstr(lookup_name, ".so");
+            }
+            ftptr = RSTRING_PTR(lookup_name);
+            if (st_lookup(vm->static_ext_inits, (st_data_t)ftptr, NULL)) {
+                *path = rb_filesystem_str_new_cstr(ftptr);
+                RB_GC_GUARD(lookup_name);
+                return 's';
+            }
         }
     }
 
@@ -1261,7 +1164,7 @@ search_required(vm_ns_t *vm_ns, VALUE fname, volatile VALUE *path, feature_func
         if (ft)
             goto feature_present;
         ftptr = RSTRING_PTR(tmp);
-        return rb_feature_p(vm_ns, ftptr, 0, FALSE, TRUE, 0);
+        return rb_feature_p(ns, ftptr, 0, FALSE, TRUE, 0);
 
       default:
         if (ft) {
@@ -1270,7 +1173,7 @@ search_required(vm_ns_t *vm_ns, VALUE fname, volatile VALUE *path, feature_func
         /* fall through */
       case loadable_ext_rb:
         ext = strrchr(ftptr = RSTRING_PTR(tmp), '.');
-        if (rb_feature_p(vm_ns, ftptr, ext, type == loadable_ext_rb, TRUE, &loading) && !loading)
+        if (rb_feature_p(ns, ftptr, ext, type == loadable_ext_rb, TRUE, &loading) && !loading)
             break;
         *path = tmp;
     }
@@ -1291,9 +1194,9 @@ static VALUE
 load_ext(VALUE path, VALUE fname)
 {
     VALUE loaded = path;
-    GET_loading_vm_ns();
-    if (NAMESPACE_USER_P(vm_ns->ns)) {
-        loaded = rb_namespace_local_extension(vm_ns->ns->ns_object, fname, path);
+    const rb_namespace_t *ns = rb_loading_namespace();
+    if (NAMESPACE_USER_P(ns)) {
+        loaded = rb_namespace_local_extension(ns->ns_object, fname, path);
     }
     rb_scope_visibility_set(METHOD_VISI_PUBLIC);
     return (VALUE)dln_load_feature(RSTRING_PTR(loaded), RSTRING_PTR(fname));
@@ -1313,7 +1216,7 @@ run_static_ext_init(rb_vm_t *vm, const char *feature)
 }
 
 static int
-no_feature_p(vm_ns_t *vm_ns, const char *feature, const char *ext, int rb, int expanded, const char **fn)
+no_feature_p(const rb_namespace_t *ns, const char *feature, const char *ext, int rb, int expanded, const char **fn)
 {
     return 0;
 }
@@ -1325,11 +1228,11 @@ rb_resolve_feature_path(VALUE klass, VALUE fname)
     VALUE path;
     int found;
     VALUE sym;
-    GET_loading_vm_ns();
+    const rb_namespace_t *ns = rb_loading_namespace();
 
     fname = rb_get_path(fname);
     path = rb_str_encode_ospath(fname);
-    found = search_required(vm_ns, path, &path, no_feature_p);
+    found = search_required(ns, path, &path, no_feature_p);
 
     switch (found) {
       case 'r':
@@ -1364,21 +1267,6 @@ rb_ext_ractor_safe(bool flag)
     GET_THREAD()->ext_config.ractor_safe = flag;
 }
 
-struct rb_vm_call_cfunc2_data {
-    VALUE recv;
-    VALUE arg1;
-    VALUE arg2;
-    VALUE block_handler;
-    VALUE filename;
-};
-
-static VALUE
-call_load_ext_in_ns(VALUE data)
-{
-    struct rb_vm_call_cfunc2_data *arg = (struct rb_vm_call_cfunc2_data *)data;
-    return rb_vm_call_cfunc2(arg->recv, load_ext, arg->arg1, arg->arg2, arg->block_handler, arg->filename);
-}
-
 /*
  * returns
  *  0: if already loaded (false)
@@ -1398,14 +1286,14 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
         th->top_wrapper, th->top_self, ec->errinfo,
         ec,
     };
-    GET_loading_vm_ns();
+    const rb_namespace_t *ns = rb_loading_namespace();
     enum ruby_tag_type state;
     char *volatile ftptr = 0;
     VALUE path;
     volatile VALUE saved_path;
     volatile VALUE realpath = 0;
-    VALUE realpaths = get_loaded_features_realpaths(vm_ns);
-    VALUE realpath_map = get_loaded_features_realpath_map(vm_ns);
+    VALUE realpaths = ns->loaded_features_realpaths;
+    VALUE realpath_map = ns->loaded_features_realpath_map;
     volatile bool reset_ext_config = false;
     volatile struct rb_ext_config prev_ext_config;
 
@@ -1421,12 +1309,12 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
         int found;
 
         RUBY_DTRACE_HOOK(FIND_REQUIRE_ENTRY, RSTRING_PTR(fname));
-        found = search_required(vm_ns, path, &saved_path, rb_feature_p);
+        found = search_required(ns, path, &saved_path, rb_feature_p);
         RUBY_DTRACE_HOOK(FIND_REQUIRE_RETURN, RSTRING_PTR(fname));
         path = saved_path;
 
         if (found) {
-            if (!path || !(ftptr = load_lock(vm_ns, RSTRING_PTR(path), warn))) {
+            if (!path || !(ftptr = load_lock(ns, RSTRING_PTR(path), warn))) {
                 result = 0;
             }
             else if (!*ftptr) {
@@ -1443,10 +1331,10 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
                 switch (found) {
                   case 'r':
                     // iseq_eval_in_namespace will be called with the loading namespace eventually
-                    if (NAMESPACE_OPTIONAL_P(vm_ns->ns)) {
+                    if (NAMESPACE_OPTIONAL_P(ns)) {
                         // check with NAMESPACE_OPTIONAL_P (not NAMESPACE_USER_P) for NS1::xxx naming
                         // it is not expected for the main namespace
-                        load_wrapping(saved.ec, path, vm_ns->ns->ns_object);
+                        load_wrapping(saved.ec, path, ns->ns_object);
                     }
                     else {
                         load_iseq_eval(saved.ec, path);
@@ -1454,19 +1342,10 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
                     break;
 
                   case 's':
-                    // the loading namespace must be set to the current namespace before calling load_ext
                     reset_ext_config = true;
                     ext_config_push(th, &prev_ext_config);
-                    struct rb_vm_call_cfunc2_data arg = {
-                        .recv = rb_vm_top_self(),
-                        .arg1 = path,
-                        .arg2 = fname,
-                        .block_handler = VM_BLOCK_HANDLER_NONE,
-                        .filename = path,
-                    };
-                    handle = rb_namespace_exec(vm_ns->ns, call_load_ext_in_ns, (VALUE)&arg);
-                    rb_hash_aset(CURRENT_NS_RUBY_DLN_LIBMAP(vm_ns, ruby_dln_libmap), path,
-                                 SVALUE2NUM((SIGNED_VALUE)handle));
+                    handle = rb_vm_call_cfunc_in_namespace(ns->top_self, load_ext, path, fname, path, ns);
+                    rb_hash_aset(ns->ruby_dln_libmap, path, SVALUE2NUM((SIGNED_VALUE)handle));
                     break;
                 }
                 result = TAG_RETURN;
@@ -1482,7 +1361,7 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
     if (reset_ext_config) ext_config_pop(th2, &prev_ext_config);
 
     path = saved_path;
-    if (ftptr) load_unlock(vm_ns, RSTRING_PTR(path), !state);
+    if (ftptr) load_unlock(ns, RSTRING_PTR(path), !state);
 
     if (state) {
         if (state == TAG_FATAL || state == TAG_THROW) {
@@ -1508,7 +1387,7 @@ require_internal(rb_execution_context_t *ec, VALUE fname, int exception, bool wa
     }
 
     if (result == TAG_RETURN) {
-        rb_provide_feature(vm_ns, path);
+        rb_provide_feature(ns, path);
         VALUE real = realpath;
         if (real) {
             real = rb_fstring(real);
@@ -1611,15 +1490,16 @@ void
 ruby_init_ext(const char *name, void (*init)(void))
 {
     st_table *inits_table;
-    GET_loading_vm_ns();
+    rb_vm_t *vm = GET_VM();
+    const rb_namespace_t *ns = rb_loading_namespace();
 
-    if (feature_provided(vm_ns, name, 0))
+    if (feature_provided((rb_namespace_t *)ns, name, 0))
         return;
 
-    inits_table = vm_ns->vm->static_ext_inits;
+    inits_table = vm->static_ext_inits;
     if (!inits_table) {
         inits_table = st_init_strtable();
-        vm_ns->vm->static_ext_inits = inits_table;
+        vm->static_ext_inits = inits_table;
     }
     st_update(inits_table, (st_data_t)name, register_init_ext, (st_data_t)init);
 }
@@ -1764,7 +1644,7 @@ rb_ext_resolve_symbol(const char* fname, const char* symbol)
     VALUE path;
     char *ext;
     VALUE fname_str = rb_str_new_cstr(fname);
-    GET_loading_vm_ns();
+    const rb_namespace_t *ns = rb_loading_namespace();
 
     resolved = rb_resolve_feature_path((VALUE)NULL, fname_str);
     if (NIL_P(resolved)) {
@@ -1772,7 +1652,7 @@ rb_ext_resolve_symbol(const char* fname, const char* symbol)
         if (!ext || !IS_SOEXT(ext)) {
             rb_str_cat_cstr(fname_str, ".so");
         }
-        if (rb_feature_p(vm_ns, fname, 0, FALSE, FALSE, 0)) {
+        if (rb_feature_p(ns, fname, 0, FALSE, FALSE, 0)) {
             return dln_symbol(NULL, symbol);
         }
         return NULL;
@@ -1781,7 +1661,7 @@ rb_ext_resolve_symbol(const char* fname, const char* symbol)
         return NULL;
     }
     path = rb_ary_entry(resolved, 1);
-    handle = rb_hash_lookup(CURRENT_NS_RUBY_DLN_LIBMAP(vm_ns, ruby_dln_libmap), path);
+    handle = rb_hash_lookup(ns->ruby_dln_libmap, path);
     if (NIL_P(handle)) {
         return NULL;
     }
@@ -1791,31 +1671,18 @@ rb_ext_resolve_symbol(const char* fname, const char* symbol)
 void
 Init_load(void)
 {
-    rb_vm_t *vm = GET_VM();
     static const char var_load_path[] = "$:";
     ID id_load_path = rb_intern2(var_load_path, sizeof(var_load_path)-1);
 
-    rb_define_hooked_variable(var_load_path, (VALUE*)vm, load_path_getter, rb_gvar_readonly_setter);
+    rb_define_hooked_variable(var_load_path, 0, load_path_getter, rb_gvar_readonly_setter);
     rb_gvar_namespace_ready(var_load_path);
     rb_alias_variable(rb_intern_const("$-I"), id_load_path);
     rb_alias_variable(rb_intern_const("$LOAD_PATH"), id_load_path);
-    vm->load_path = rb_ary_new();
-    vm->expanded_load_path = rb_ary_hidden_new(0);
-    vm->load_path_snapshot = rb_ary_hidden_new(0);
-    vm->load_path_check_cache = 0;
-    rb_define_singleton_method(vm->load_path, "resolve_feature_path", rb_resolve_feature_path, 1);
 
     rb_define_virtual_variable("$\"", get_LOADED_FEATURES, 0);
     rb_gvar_namespace_ready("$\"");
     rb_define_virtual_variable("$LOADED_FEATURES", get_LOADED_FEATURES, 0); // TODO: rb_alias_variable ?
     rb_gvar_namespace_ready("$LOADED_FEATURES");
-    vm->loaded_features = rb_ary_new();
-    vm->loaded_features_snapshot = rb_ary_hidden_new(0);
-    vm->loaded_features_index = st_init_numtable();
-    vm->loaded_features_realpaths = rb_hash_new();
-    rb_obj_hide(vm->loaded_features_realpaths);
-    vm->loaded_features_realpath_map = rb_hash_new();
-    rb_obj_hide(vm->loaded_features_realpath_map);
 
     rb_define_global_function("load", rb_f_load, -1);
     rb_define_global_function("require", rb_f_require, 1);
@@ -1824,7 +1691,4 @@ Init_load(void)
     rb_define_method(rb_cModule, "autoload?", rb_mod_autoload_p, -1);
     rb_define_global_function("autoload", rb_f_autoload, 2);
     rb_define_global_function("autoload?", rb_f_autoload_p, -1);
-
-    ruby_dln_libmap = rb_hash_new_with_size(0);
-    rb_vm_register_global_object(ruby_dln_libmap);
 }
diff --git a/mini_builtin.c b/mini_builtin.c
index d9827e70e4..3ff3dc5c1d 100644
--- a/mini_builtin.c
+++ b/mini_builtin.c
@@ -96,24 +96,9 @@ builtin_iseq_load(const char *feature_name, const struct rb_builtin_function *ta
     return iseq;
 }
 
-static void
-load_with_builtin_functions(const char *feature_name, const struct rb_builtin_function *table)
-{
-    const rb_iseq_t *iseq = builtin_iseq_load(feature_name, table);
-    rb_namespace_enable_builtin();
-    rb_iseq_eval_with_refinement(iseq, rb_mNamespaceRefiner);
-    rb_namespace_disable_builtin();
-}
-
 void
 rb_load_with_builtin_functions(const char *feature_name, const struct rb_builtin_function *table)
 {
-    const rb_iseq_t *iseq;
-    if (rb_namespace_available() && rb_mNamespaceRefiner) {
-        load_with_builtin_functions(feature_name, table);
-    }
-    else {
-        iseq = builtin_iseq_load(feature_name, table);
-        rb_iseq_eval(iseq);
-    }
+    const rb_iseq_t *iseq = builtin_iseq_load(feature_name, table);
+    rb_iseq_eval(iseq, rb_root_namespace());
 }
diff --git a/namespace.c b/namespace.c
index 55b7580c72..2ccc3db94d 100644
--- a/namespace.c
+++ b/namespace.c
@@ -1,5 +1,6 @@
 /* indent-tabs-mode: nil */
 
+#include "eval_intern.h"
 #include "internal.h"
 #include "internal/class.h"
 #include "internal/eval.h"
@@ -11,6 +12,7 @@
 #include "internal/namespace.h"
 #include "internal/st.h"
 #include "internal/variable.h"
+#include "iseq.h"
 #include "ruby/internal/globals.h"
 #include "ruby/util.h"
 #include "vm_core.h"
@@ -19,18 +21,17 @@
 
 VALUE rb_cNamespace = 0;
 VALUE rb_cNamespaceEntry = 0;
-VALUE rb_mNamespaceRefiner = 0;
 VALUE rb_mNamespaceLoader = 0;
 
-static rb_namespace_t builtin_namespace_data = {
-    .ns_object = Qnil,
-    .ns_id = 0,
-    .is_builtin = true,
-    .is_user = false,
-    .is_optional = false
+static rb_namespace_t root_namespace_data = {
+    /* Initialize values lazily in Init_namespace() */
+    (VALUE)NULL, 0,
+    (VALUE)NULL, (VALUE)NULL, (VALUE)NULL, (VALUE)NULL, (VALUE)NULL, (VALUE)NULL, (VALUE)NULL, (VALUE)NULL, (VALUE)NULL,
+    (struct st_table *)NULL, (struct st_table *)NULL, (VALUE)NULL, (VALUE)NULL,
+    false, false
 };
-static rb_namespace_t * const root_namespace = 0;
-static rb_namespace_t * const builtin_namespace = &builtin_namespace_data;
+
+static rb_namespace_t * root_namespace = &root_namespace_data;
 static rb_namespace_t * main_namespace = 0;
 static char *tmp_dir;
 static bool tmp_dir_has_dirsep;
@@ -52,8 +53,6 @@ bool ruby_namespace_init_done = false; // extern
 
 VALUE rb_resolve_feature_path(VALUE klass, VALUE fname);
 static VALUE rb_namespace_inspect(VALUE obj);
-static void namespace_push(rb_thread_t *th, VALUE namespace);
-static VALUE namespace_pop(VALUE th_value);
 
 void
 rb_namespace_init_done(void)
@@ -61,211 +60,41 @@ rb_namespace_init_done(void)
     ruby_namespace_init_done = true;
 }
 
-void
-rb_namespace_enable_builtin(void)
-{
-    VALUE require_stack = GET_VM()->require_stack;
-    if (require_stack) {
-        rb_ary_push(require_stack, Qnil);
-    }
-}
-
-void
-rb_namespace_disable_builtin(void)
-{
-    VALUE require_stack = GET_VM()->require_stack;
-    if (require_stack) {
-        rb_ary_pop(require_stack);
-    }
-}
-
-void
-rb_namespace_push_loading_namespace(const rb_namespace_t *ns)
-{
-    VALUE require_stack = GET_VM()->require_stack;
-    rb_ary_push(require_stack, ns->ns_object);
-}
-
-void
-rb_namespace_pop_loading_namespace(const rb_namespace_t *ns)
-{
-    VALUE require_stack = GET_VM()->require_stack;
-    long size = RARRAY_LEN(require_stack);
-    if (size == 0)
-        rb_bug("popping on the empty require_stack");
-    VALUE latest = RARRAY_AREF(require_stack, size-1);
-    if (latest != ns->ns_object)
-        rb_bug("Inconsistent loading namespace");
-    rb_ary_pop(require_stack);
-}
-
-rb_namespace_t *
+const rb_namespace_t *
 rb_root_namespace(void)
 {
     return root_namespace;
 }
 
 const rb_namespace_t *
-rb_builtin_namespace(void)
-{
-    return (const rb_namespace_t *)builtin_namespace;
-}
-
-rb_namespace_t *
 rb_main_namespace(void)
 {
     return main_namespace;
 }
 
-static bool
-namespace_ignore_builtin_primitive_methods_p(const rb_namespace_t *ns, rb_method_definition_t *def)
-{
-    if (!NAMESPACE_BUILTIN_P(ns)) {
-        return false;
-    }
-    /* Primitive methods (just to call C methods) covers/hides the effective
-       namespaces, so ignore the methods' namespaces to expose user code's
-       namespace to the implementation.
-     */
-    if (def->type == VM_METHOD_TYPE_ISEQ) {
-        ID mid = def->original_id;
-        const char *path = RSTRING_PTR(pathobj_path(def->body.iseq.iseqptr->body->location.pathobj));
-        if (strcmp(path, "<internal:kernel>") == 0) {
-            if (mid == rb_intern("class") || mid == rb_intern("clone") ||
-                mid == rb_intern("tag") || mid == rb_intern("then") ||
-                mid == rb_intern("yield_self") || mid == rb_intern("loop") ||
-                mid == rb_intern("Float") || mid == rb_intern("Integer")
-                ) {
-                return true;
-            }
-        }
-        else if (strcmp(path, "<internal:warning>") == 0) {
-            if (mid == rb_intern("warn")) {
-                return true;
-            }
-        }
-        else if (strcmp(path, "<internal:marshal>") == 0) {
-            if (mid == rb_intern("load"))
-                return true;
-        }
-    }
-    return false;
-}
-
-static inline const rb_namespace_t *
-block_proc_namespace(const VALUE procval)
-{
-    rb_proc_t *proc;
-
-    if (procval) {
-        GetProcPtr(procval, proc);
-        return proc->ns;
-    }
-    else {
-        return NULL;
-    }
-}
-
-static const rb_namespace_t *
-current_namespace(bool permit_calling_builtin)
-{
-    /*
-     * TODO: move this code to vm.c or somewhere else
-     *       when it's fully updated with VM_FRAME_FLAG_*
-     */
-    const rb_callable_method_entry_t *cme;
-    const rb_namespace_t *ns;
-    rb_execution_context_t *ec = GET_EC();
-    rb_control_frame_t *cfp = ec->cfp;
-    rb_thread_t *th = rb_ec_thread_ptr(ec);
-    int calling = 1;
-
-    if (!rb_namespace_available())
-        return 0;
-
-    if (th->namespaces && RARRAY_LEN(th->namespaces) > 0) {
-        // temp code to detect the context is in require/load
-        // TODO: this doesn't work well in optional namespaces
-        // calling = 0;
-    }
-    while (calling) {
-        const rb_namespace_t *proc_ns = NULL;
-        VALUE bh;
-        if (VM_FRAME_NS_SWITCH_P(cfp)) {
-            bh = rb_vm_frame_block_handler(cfp);
-            if (bh && vm_block_handler_type(bh) == block_handler_type_proc) {
-                proc_ns = block_proc_namespace(VM_BH_TO_PROC(bh));
-                if (permit_calling_builtin || NAMESPACE_USER_P(proc_ns))
-                    return proc_ns;
-            }
-        }
-        cme = rb_vm_frame_method_entry(cfp);
-        if (cme && cme->def) {
-            ns = cme->def->ns;
-            if (ns) {
-                // this method is not a built-in class/module's method
-                // or a built-in primitive (Ruby) method
-                if (!namespace_ignore_builtin_primitive_methods_p(ns, cme->def)) {
-                    if (permit_calling_builtin || (proc_ns && NAMESPACE_USER_P(proc_ns)))
-                        return ns;
-                }
-            }
-            cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
-        }
-        else {
-            calling = 0;
-        }
-    }
-    // not in namespace-marked method calls
-    ns = th->ns;
-    if (ns) {
-        return ns;
-    }
-    if (!main_namespace) {
-        // Namespaces are not ready to be created
-        return root_namespace;
-    }
-    return main_namespace;
-}
-
 const rb_namespace_t *
 rb_current_namespace(void)
 {
-    return current_namespace(true);
+    /*
+     * If RUBY_NAMESPACE is not set, the root namespace is the only available one.
+     *
+     * Until the main_namespace is not initialized, the root namespace is
+     * the only valid namespace.
+     * This early return is to avoid accessing EC before its setup.
+     */
+    if (!main_namespace)
+        return root_namespace;
+
+    return rb_vm_current_namespace(GET_EC());
 }
 
 const rb_namespace_t *
 rb_loading_namespace(void)
 {
-    VALUE namespace;
-    long len;
-    VALUE require_stack = GET_VM()->require_stack;
-
-    if (!rb_namespace_available())
-        return 0;
-
-    if (!require_stack) {
-        return current_namespace(false);
-    }
-    if ((len = RARRAY_LEN(require_stack)) == 0) {
-        return current_namespace(false);
-    }
-
-    if (!RB_TYPE_P(require_stack, T_ARRAY))
-        rb_bug("require_stack is not an array: %s", rb_type_str(BUILTIN_TYPE(require_stack)));
-
-    namespace = RARRAY_AREF(require_stack, len-1);
-    return rb_get_namespace_t(namespace);
-}
-
-const rb_namespace_t *
-rb_definition_namespace(void)
-{
-    const rb_namespace_t *ns = current_namespace(true);
-    if (NAMESPACE_BUILTIN_P(ns)) {
+    if (!main_namespace)
         return root_namespace;
-    }
-    return ns;
+
+    return rb_vm_loading_namespace(GET_EC());
 }
 
 static long namespace_id_counter = 0;
@@ -283,37 +112,43 @@ namespace_generate_id(void)
 static void
 namespace_entry_initialize(rb_namespace_t *ns)
 {
-    rb_vm_t *vm = GET_VM();
+    const rb_namespace_t *root = rb_root_namespace();
 
     // These will be updated immediately
     ns->ns_object = 0;
     ns->ns_id = 0;
 
-    ns->top_self = 0;
-    ns->load_path = rb_ary_dup(vm->load_path);
-    ns->expanded_load_path = rb_ary_dup(vm->expanded_load_path);
+    ns->top_self = rb_obj_alloc(rb_cObject);
+    // TODO:
+    // rb_define_singleton_method(rb_vm_top_self(), "to_s", main_to_s, 0);
+    // rb_define_alias(rb_singleton_class(rb_vm_top_self()), "inspect", "to_s");
+    ns->load_path = rb_ary_dup(root->load_path);
+    ns->expanded_load_path = rb_ary_dup(root->expanded_load_path);
     ns->load_path_snapshot = rb_ary_new();
     ns->load_path_check_cache = 0;
-    ns->loaded_features = rb_ary_dup(vm->loaded_features);
+    ns->loaded_features = rb_ary_dup(root->loaded_features);
     ns->loaded_features_snapshot = rb_ary_new();
     ns->loaded_features_index = st_init_numtable();
-    ns->loaded_features_realpaths = rb_hash_dup(vm->loaded_features_realpaths);
-    ns->loaded_features_realpath_map = rb_hash_dup(vm->loaded_features_realpath_map);
+    ns->loaded_features_realpaths = rb_hash_dup(root->loaded_features_realpaths);
+    ns->loaded_features_realpath_map = rb_hash_dup(root->loaded_features_realpath_map);
     ns->loading_table = st_init_strtable();
     ns->ruby_dln_libmap = rb_hash_new_with_size(0);
     ns->gvar_tbl = rb_hash_new_with_size(0);
 
-    ns->is_builtin = false;
     ns->is_user = true;
     ns->is_optional = true;
 }
 
-void rb_namespace_gc_update_references(void *ptr)
+void
+rb_namespace_gc_update_references(void *ptr)
 {
     rb_namespace_t *ns = (rb_namespace_t *)ptr;
-    if (!NIL_P(ns->ns_object))
+    if (!ns) return;
+
+    if (ns->ns_object)
         ns->ns_object = rb_gc_location(ns->ns_object);
-    ns->top_self = rb_gc_location(ns->top_self);
+    if (ns->top_self)
+        ns->top_self = rb_gc_location(ns->top_self);
     ns->load_path = rb_gc_location(ns->load_path);
     ns->expanded_load_path = rb_gc_location(ns->expanded_load_path);
     ns->load_path_snapshot = rb_gc_location(ns->load_path_snapshot);
@@ -332,6 +167,8 @@ void
 rb_namespace_entry_mark(void *ptr)
 {
     const rb_namespace_t *ns = (rb_namespace_t *)ptr;
+    if (!ns) return;
+
     rb_gc_mark(ns->ns_object);
     rb_gc_mark(ns->top_self);
     rb_gc_mark(ns->load_path);
@@ -349,11 +186,26 @@ rb_namespace_entry_mark(void *ptr)
     rb_gc_mark(ns->gvar_tbl);
 }
 
+// TODO: implemente namespace_entry_free to free loading_table etc
+/*
+static int
+free_loading_table_entry(st_data_t key, st_data_t value, st_data_t arg)
+{
+    xfree((char *)key);
+    return ST_DELETE;
+}
+        if (vm->loading_table) {
+            st_foreach(vm->loading_table, free_loading_table_entry, 0);
+            st_free_table(vm->loading_table);
+            vm->loading_table = 0;
+        }
+*/
 #define namespace_entry_free RUBY_TYPED_DEFAULT_FREE
 
 static size_t
 namespace_entry_memsize(const void *ptr)
 {
+    // TODO: rb_st_memsize(loaded_features_index) + rb_st_memsize(vm->loading_table)
     return sizeof(rb_namespace_t);
 }
 
@@ -391,10 +243,12 @@ rb_get_namespace_t(VALUE namespace)
     VALUE entry;
     ID id_namespace_entry;
 
-    if (!namespace)
-        return root_namespace;
+    VM_ASSERT(namespace);
+
     if (NIL_P(namespace))
-        return builtin_namespace;
+        return root_namespace;
+
+    VM_ASSERT(NAMESPACE_OBJ_P(namespace));
 
     CONST_ID(id_namespace_entry, "__namespace_entry__");
     entry = rb_attr_get(namespace, id_namespace_entry);
@@ -404,13 +258,10 @@ rb_get_namespace_t(VALUE namespace)
 VALUE
 rb_get_namespace_object(rb_namespace_t *ns)
 {
-    if (!ns) // root namespace
-        return Qfalse;
+    VM_ASSERT(ns && ns->ns_object);
     return ns->ns_object;
 }
 
-static void setup_pushing_loading_namespace(rb_namespace_t *ns);
-
 /*
  *  call-seq:
  *    Namespace.new -> new_namespace
@@ -435,8 +286,6 @@ namespace_initialize(VALUE namespace)
 
     ns->ns_object = namespace;
     ns->ns_id = namespace_generate_id();
-    ns->load_path = rb_ary_dup(GET_VM()->load_path);
-    ns->is_user = true;
     rb_define_singleton_method(ns->load_path, "resolve_feature_path", rb_resolve_feature_path, 1);
 
     // Set the Namespace object unique/consistent from any namespaces to have just single
@@ -451,8 +300,6 @@ namespace_initialize(VALUE namespace)
 
     rb_ivar_set(namespace, id_namespace_entry, entry);
 
-    setup_pushing_loading_namespace(ns);
-
     return namespace;
 }
 
@@ -463,7 +310,7 @@ namespace_initialize(VALUE namespace)
  *  Returns +true+ if namespace is enabled.
  */
 static VALUE
-rb_namespace_s_getenabled(VALUE namespace)
+rb_namespace_s_getenabled(VALUE recv)
 {
     return RBOOL(rb_namespace_available());
 }
@@ -477,16 +324,16 @@ rb_namespace_s_getenabled(VALUE namespace)
  *  Returns +false+ if namespace is not enabled.
  */
 static VALUE
-rb_namespace_current(VALUE klass)
+rb_namespace_s_current(VALUE recv)
 {
-    const rb_namespace_t *ns = rb_current_namespace();
-    if (NAMESPACE_USER_P(ns)) {
-        return ns->ns_object;
-    }
-    if (NAMESPACE_BUILTIN_P(ns)) {
+    const rb_namespace_t *ns;
+
+    if (!rb_namespace_available())
         return Qnil;
-    }
-    return Qfalse;
+
+    ns = rb_vm_current_namespace(GET_EC());
+    VM_ASSERT(ns && ns->ns_object);
+    return ns->ns_object;
 }
 
 /*
@@ -496,7 +343,7 @@ rb_namespace_current(VALUE klass)
  *  Returns +true+ if +klass+ is only in a user namespace.
  */
 static VALUE
-rb_namespace_s_is_builtin_p(VALUE namespace, VALUE klass)
+rb_namespace_s_is_builtin_p(VALUE recv, VALUE klass)
 {
     if (RCLASS_PRIME_CLASSEXT_READABLE_P(klass) && !RCLASS_PRIME_CLASSEXT_WRITABLE_P(klass))
         return Qtrue;
@@ -512,6 +359,7 @@ rb_namespace_s_is_builtin_p(VALUE namespace, VALUE klass)
 static VALUE
 rb_namespace_load_path(VALUE namespace)
 {
+    VM_ASSERT(NAMESPACE_OBJ_P(namespace));
     return rb_get_namespace_t(namespace)->load_path;
 }
 
@@ -787,125 +635,94 @@ rb_namespace_local_extension(VALUE namespace, VALUE fname, VALUE path)
 //       At least for _WIN32, deleting extension files should be delayed until the namespace's destructor.
 //       And it requires calling dlclose before deleting it.
 
-static void
-namespace_push(rb_thread_t *th, VALUE namespace)
-{
-    if (RTEST(th->namespaces)) {
-        rb_ary_push(th->namespaces, namespace);
-    }
-    else {
-        th->namespaces = rb_ary_new_from_args(1, namespace);
-    }
-    th->ns = rb_get_namespace_t(namespace);
-}
-
-static VALUE
-namespace_pop(VALUE th_value)
-{
-    VALUE upper_ns;
-    long stack_len;
-    rb_thread_t *th = (rb_thread_t *)th_value;
-    VALUE namespaces = th->namespaces;
-    if (!namespaces) {
-        rb_bug("Too many namespace pops");
-    }
-    rb_ary_pop(namespaces);
-    stack_len = RARRAY_LEN(namespaces);
-    if (stack_len == 0) {
-        th->namespaces = 0;
-        th->ns = main_namespace;
-    }
-    else {
-        upper_ns = RARRAY_AREF(namespaces, stack_len-1);
-        th->ns = rb_get_namespace_t(upper_ns);
-    }
-    return Qnil;
-}
-
-VALUE
-rb_namespace_exec(const rb_namespace_t *ns, namespace_exec_func *func, VALUE arg)
-{
-    rb_thread_t *th = GET_THREAD();
-    namespace_push(th, ns ? ns->ns_object : Qnil);
-    return rb_ensure(func, arg, namespace_pop, (VALUE)th);
-}
-
-struct namespace_pop2_arg {
-    rb_thread_t *th;
-    rb_namespace_t *ns;
-};
-
-static VALUE
-namespace_both_pop(VALUE arg)
-{
-    struct namespace_pop2_arg *data = (struct namespace_pop2_arg *)arg;
-    namespace_pop((VALUE) data->th);
-    rb_namespace_pop_loading_namespace(data->ns);
-    return Qnil;
-}
-
 static VALUE
 rb_namespace_load(int argc, VALUE *argv, VALUE namespace)
 {
     VALUE fname, wrap;
-    rb_thread_t *th = GET_THREAD();
-    rb_namespace_t *ns = rb_get_namespace_t(namespace);
-
     rb_scan_args(argc, argv, "11", &fname, &wrap);
 
+    rb_vm_frame_flag_set_ns_require(GET_EC());
+
     VALUE args = rb_ary_new_from_args(2, fname, wrap);
-    namespace_push(th, namespace);
-    rb_namespace_push_loading_namespace(ns);
-    struct namespace_pop2_arg arg = {
-        .th = th,
-        .ns = ns
-    };
-    return rb_ensure(rb_load_entrypoint, args, namespace_both_pop, (VALUE)&arg);
+    return rb_load_entrypoint(args);
 }
 
 static VALUE
 rb_namespace_require(VALUE namespace, VALUE fname)
 {
-    rb_thread_t *th = GET_THREAD();
-    rb_namespace_t *ns = rb_get_namespace_t(namespace);
-    namespace_push(th, namespace);
-    rb_namespace_push_loading_namespace(ns);
-    struct namespace_pop2_arg arg = {
-        .th = th,
-        .ns = ns
-    };
-    return rb_ensure(rb_require_string, fname, namespace_both_pop, (VALUE)&arg);
+    rb_vm_frame_flag_set_ns_require(GET_EC());
+
+    return rb_require_string(fname);
 }
 
 static VALUE
 rb_namespace_require_relative(VALUE namespace, VALUE fname)
 {
-    rb_thread_t *th = GET_THREAD();
-    rb_namespace_t *ns = rb_get_namespace_t(namespace);
-    namespace_push(th, namespace);
-    rb_namespace_push_loading_namespace(ns);
-    struct namespace_pop2_arg arg = {
-        .th = th,
-        .ns = ns
-    };
-    return rb_ensure(rb_require_relative_entrypoint, fname, namespace_both_pop, (VALUE)&arg);
+    rb_vm_frame_flag_set_ns_require(GET_EC());
+
+    return rb_require_relative_entrypoint(fname);
 }
 
-static VALUE
-rb_namespace_eval_string(VALUE str)
+static void
+initialize_root_namespace(void)
 {
-    return rb_eval_string(RSTRING_PTR(str));
+    VALUE root_namespace, entry;
+    ID id_namespace_entry;
+    rb_vm_t *vm = GET_VM();
+    rb_namespace_t *root = (rb_namespace_t *)rb_root_namespace();
+
+    root->load_path = rb_ary_new();
+    root->expanded_load_path = rb_ary_hidden_new(0);
+    root->load_path_snapshot = rb_ary_hidden_new(0);
+    root->load_path_check_cache = 0;
+    rb_define_singleton_method(root->load_path, "resolve_feature_path", rb_resolve_feature_path, 1);
+
+    root->loaded_features = rb_ary_new();
+    root->loaded_features_snapshot = rb_ary_hidden_new(0);
+    root->loaded_features_index = st_init_numtable();
+    root->loaded_features_realpaths = rb_hash_new();
+    rb_obj_hide(root->loaded_features_realpaths);
+    root->loaded_features_realpath_map = rb_hash_new();
+    rb_obj_hide(root->loaded_features_realpath_map);
+
+    root->ruby_dln_libmap = rb_hash_new_with_size(0);
+    root->gvar_tbl = rb_hash_new_with_size(0);
+
+    vm->root_namespace = root;
+
+    if (rb_namespace_available()) {
+        CONST_ID(id_namespace_entry, "__namespace_entry__");
+
+        root_namespace = rb_obj_alloc(rb_cNamespace);
+        RCLASS_SET_PRIME_CLASSEXT_WRITABLE(root_namespace, true);
+        RCLASS_SET_CONST_TBL(root_namespace, RCLASSEXT_CONST_TBL(RCLASS_EXT_PRIME(rb_cObject)), true);
+
+        root->ns_id = namespace_generate_id();
+        root->ns_object = root_namespace;
+
+        entry = TypedData_Wrap_Struct(rb_cNamespaceEntry, &rb_namespace_data_type, root);
+        rb_ivar_set(root_namespace, id_namespace_entry, entry);
+    }
+    else {
+        root->ns_id = 1;
+        root->ns_object = Qnil;
+    }
 }
 
 static VALUE
 rb_namespace_eval(VALUE namespace, VALUE str)
 {
-    rb_thread_t *th = GET_THREAD();
+    const rb_iseq_t *iseq;
+    const rb_namespace_t *ns;
 
     StringValue(str);
 
-    namespace_push(th, namespace);
-    return rb_ensure(rb_namespace_eval_string, str, namespace_pop, (VALUE)th);
+    iseq = rb_iseq_compile_iseq(str, rb_str_new_cstr("eval"));
+    VM_ASSERT(iseq);
+
+    ns = (const rb_namespace_t *)rb_get_namespace_t(namespace);
+
+    return rb_iseq_eval(iseq, ns);
 }
 
 static int namespace_experimental_warned = 0;
@@ -914,9 +731,10 @@ void
 rb_initialize_main_namespace(void)
 {
     rb_namespace_t *ns;
-    rb_vm_t *vm = GET_VM();
-    rb_thread_t *th = GET_THREAD();
     VALUE main_ns;
+    rb_vm_t *vm = GET_VM();
+
+    VM_ASSERT(rb_namespace_available());
 
     if (!namespace_experimental_warned) {
         rb_category_warn(RB_WARN_CATEGORY_EXPERIMENTAL,
@@ -925,17 +743,17 @@ rb_initialize_main_namespace(void)
         namespace_experimental_warned = 1;
     }
 
-    main_ns = rb_class_new_instance_pass_kw(0, NULL, rb_cNamespace);
+    main_ns = rb_class_new_instance(0, NULL, rb_cNamespace);
+    VM_ASSERT(NAMESPACE_OBJ_P(main_ns));
     ns = rb_get_namespace_t(main_ns);
     ns->ns_object = main_ns;
     ns->ns_id = namespace_generate_id();
-    ns->is_builtin = false;
     ns->is_user = true;
     ns->is_optional = false;
 
     rb_const_set(rb_cNamespace, rb_intern("MAIN"), main_ns);
 
-    vm->main_namespace = th->ns = main_namespace = ns;
+    vm->main_namespace = main_namespace = ns;
 }
 
 static VALUE
@@ -950,8 +768,8 @@ rb_namespace_inspect(VALUE obj)
     ns = rb_get_namespace_t(obj);
     r = rb_str_new_cstr("#<Namespace:");
     rb_str_concat(r, rb_funcall(LONG2NUM(ns->ns_id), rb_intern("to_s"), 0));
-    if (NAMESPACE_BUILTIN_P(ns)) {
-        rb_str_cat_cstr(r, ",builtin");
+    if (NAMESPACE_ROOT_P(ns)) {
+        rb_str_cat_cstr(r, ",root");
     }
     if (NAMESPACE_USER_P(ns)) {
         rb_str_cat_cstr(r, ",user");
@@ -966,106 +784,24 @@ rb_namespace_inspect(VALUE obj)
     return r;
 }
 
-struct refiner_calling_super_data {
-    int argc;
-    VALUE *argv;
-};
-
 static VALUE
-namespace_builtin_refiner_calling_super(VALUE arg)
+rb_namespace_loading_func(int argc, VALUE *argv, VALUE _self)
 {
-    struct refiner_calling_super_data *data = (struct refiner_calling_super_data *)arg;
-    return rb_call_super(data->argc, data->argv);
-}
-
-static VALUE
-namespace_builtin_refiner_loading_func_ensure(VALUE _)
-{
-    rb_vm_t *vm = GET_VM();
-    if (!vm->require_stack)
-        rb_bug("require_stack is not ready but the namespace refiner is called");
-    rb_namespace_disable_builtin();
-    return Qnil;
-}
-
-static VALUE
-rb_namespace_builtin_refiner_loading_func(int argc, VALUE *argv, VALUE _self)
-{
-    rb_vm_t *vm = GET_VM();
-    if (!vm->require_stack)
-        rb_bug("require_stack is not ready but the namespace refiner is called");
-    rb_namespace_enable_builtin();
-    // const rb_namespace_t *ns = rb_loading_namespace();
-    // printf("N:current loading ns: %ld\n", ns->ns_id);
-    struct refiner_calling_super_data data = {
-        .argc = argc,
-        .argv = argv
-    };
-    return rb_ensure(namespace_builtin_refiner_calling_super, (VALUE)&data,
-                     namespace_builtin_refiner_loading_func_ensure, Qnil);
-}
-
-static void
-setup_builtin_refinement(VALUE mod)
-{
-    struct rb_refinements_data data;
-    rb_refinement_setup(&data, mod, rb_mKernel);
-    rb_define_method(data.refinement, "require", rb_namespace_builtin_refiner_loading_func, -1);
-    rb_define_method(data.refinement, "require_relative", rb_namespace_builtin_refiner_loading_func, -1);
-    rb_define_method(data.refinement, "load", rb_namespace_builtin_refiner_loading_func, -1);
-}
-
-static VALUE
-namespace_user_loading_func_calling_super(VALUE arg)
-{
-    struct refiner_calling_super_data *data = (struct refiner_calling_super_data *)arg;
-    return rb_call_super(data->argc, data->argv);
-}
-
-static VALUE
-namespace_user_loading_func_ensure(VALUE arg)
-{
-    rb_namespace_t *ns = (rb_namespace_t *)arg;
-    rb_namespace_pop_loading_namespace(ns);
-    return Qnil;
-}
-
-static VALUE
-rb_namespace_user_loading_func(int argc, VALUE *argv, VALUE _self)
-{
-    const rb_namespace_t *ns;
-    rb_vm_t *vm = GET_VM();
-    if (!vm->require_stack)
-        rb_bug("require_stack is not ready but require/load is called in user namespaces");
-    ns = rb_current_namespace();
-    VM_ASSERT(rb_namespace_available() || !ns);
-    rb_namespace_push_loading_namespace(ns);
-    struct refiner_calling_super_data data = {
-        .argc = argc,
-        .argv = argv
-    };
-    return rb_ensure(namespace_user_loading_func_calling_super, (VALUE)&data,
-                     namespace_user_loading_func_ensure, (VALUE)ns);
-}
-
-static VALUE
-setup_pushing_loading_namespace_include(VALUE mod)
-{
-    rb_include_module(rb_cObject, mod);
-    return Qnil;
-}
-
-static void
-setup_pushing_loading_namespace(rb_namespace_t *ns)
-{
-    rb_namespace_exec(ns, setup_pushing_loading_namespace_include, rb_mNamespaceLoader);
+    rb_vm_frame_flag_set_ns_require(GET_EC());
+    return rb_call_super(argc, argv);
 }
 
 static void
 namespace_define_loader_method(const char *name)
 {
-    rb_define_private_method(rb_mNamespaceLoader, name, rb_namespace_user_loading_func, -1);
-    rb_define_singleton_method(rb_mNamespaceLoader, name, rb_namespace_user_loading_func, -1);
+    rb_define_private_method(rb_mNamespaceLoader, name, rb_namespace_loading_func, -1);
+    rb_define_singleton_method(rb_mNamespaceLoader, name, rb_namespace_loading_func, -1);
+}
+
+void
+Init_root_namespace(void)
+{
+    root_namespace->loading_table = st_init_strtable();
 }
 
 void
@@ -1080,6 +816,140 @@ Init_enable_namespace(void)
     }
 }
 
+#ifdef RUBY_DEBUG
+
+static const char *
+classname(VALUE klass)
+{
+    VALUE p = RCLASS_CLASSPATH(klass);
+    if (RTEST(p))
+        return RSTRING_PTR(p);
+    if (RB_TYPE_P(klass, T_CLASS) || RB_TYPE_P(klass, T_MODULE) || RB_TYPE_P(klass, T_ICLASS))
+        return RSTRING_PTR(rb_inspect(klass));
+    return "NonClassValue";
+}
+
+static enum rb_id_table_iterator_result
+dump_classext_methods_i(ID mid, VALUE _val, void *data)
+{
+    VALUE ary = (VALUE)data;
+    rb_ary_push(ary, rb_id2str(mid));
+    return ID_TABLE_CONTINUE;
+}
+
+static enum rb_id_table_iterator_result
+dump_classext_constants_i(ID mid, VALUE _val, void *data)
+{
+    VALUE ary = (VALUE)data;
+    rb_ary_push(ary, rb_id2str(mid));
+    return ID_TABLE_CONTINUE;
+}
+
+static void
+dump_classext_i(rb_classext_t *ext, bool is_prime, VALUE _ns, void *data)
+{
+    char buf[4096];
+    struct rb_id_table *tbl;
+    VALUE ary, res = (VALUE)data;
+
+    snprintf(buf, 4096, "Namespace %ld:%s classext %p\n",
+             RCLASSEXT_NS(ext)->ns_id, is_prime ? " prime" : "", (void *)ext);
+    rb_str_cat_cstr(res, buf);
+
+    snprintf(buf, 2048, "  Super: %s\n", classname(RCLASSEXT_SUPER(ext)));
+    rb_str_cat_cstr(res, buf);
+
+    tbl = RCLASSEXT_M_TBL(ext);
+    if (tbl) {
+        ary = rb_ary_new_capa((long)rb_id_table_size(tbl));
+        rb_id_table_foreach(RCLASSEXT_M_TBL(ext), dump_classext_methods_i, (void *)ary);
+        rb_ary_sort_bang(ary);
+        snprintf(buf, 4096, "  Methods(%ld): ", RARRAY_LEN(ary));
+        rb_str_cat_cstr(res, buf);
+        rb_str_concat(res, rb_ary_join(ary, rb_str_new_cstr(",")));
+        rb_str_cat_cstr(res, "\n");
+    }
+    else {
+        rb_str_cat_cstr(res, "  Methods(0): .\n");
+    }
+
+    tbl = RCLASSEXT_CONST_TBL(ext);
+    if (tbl) {
+        ary = rb_ary_new_capa((long)rb_id_table_size(tbl));
+        rb_id_table_foreach(tbl, dump_classext_constants_i, (void *)ary);
+        rb_ary_sort_bang(ary);
+        snprintf(buf, 4096, "  Constants(%ld): ", RARRAY_LEN(ary));
+        rb_str_cat_cstr(res, buf);
+        rb_str_concat(res, rb_ary_join(ary, rb_str_new_cstr(",")));
+        rb_str_cat_cstr(res, "\n");
+    }
+    else {
+        rb_str_cat_cstr(res, "  Constants(0): .\n");
+    }
+}
+
+static VALUE
+rb_f_dump_classext(VALUE recv, VALUE klass)
+{
+    /*
+     * The desired output String value is:
+     * Class: 0x88800932 (String) [singleton]
+     * Prime classext namespace(2,main), readable(t), writable(f)
+     * Non-prime classexts: 3
+     * Namespace 2: prime classext 0x88800933
+     *   Super: Object
+     *   Methods(43): aaaaa, bbbb, cccc, dddd, eeeee, ffff, gggg, hhhhh, ...
+     *   Constants(12): FOO, Bar, ...
+     * Namespace 5: classext 0x88800934
+     *   Super: Object
+     *   Methods(43): aaaaa, bbbb, cccc, dddd, eeeee, ffff, gggg, hhhhh, ...
+     *   Constants(12): FOO, Bar, ...
+     */
+    char buf[2048];
+    VALUE res;
+    const rb_classext_t *ext;
+    const rb_namespace_t *ns;
+    st_table *classext_tbl;
+
+    if (!(RB_TYPE_P(klass, T_CLASS) || RB_TYPE_P(klass, T_MODULE))) {
+        snprintf(buf, 2048, "Non-class/module value: %p (%s)\n", (void *)klass, rb_type_str(BUILTIN_TYPE(klass)));
+        return rb_str_new_cstr(buf);
+    }
+
+    if (RB_TYPE_P(klass, T_CLASS)) {
+        snprintf(buf, 2048, "Class: %p (%s)%s\n",
+                 (void *)klass, classname(klass), RCLASS_SINGLETON_P(klass) ? " [singleton]" : "");
+    }
+    else {
+        snprintf(buf, 2048, "Module: %p (%s)\n", (void *)klass, classname(klass));
+    }
+    res = rb_str_new_cstr(buf);
+
+    ext = RCLASS_EXT_PRIME(klass);
+    ns = RCLASSEXT_NS(ext);
+    snprintf(buf, 2048, "Prime classext namespace(%ld,%s), readable(%s), writable(%s)\n",
+             ns->ns_id,
+             NAMESPACE_ROOT_P(ns) ? "root" : (NAMESPACE_MAIN_P(ns) ? "main" : "optional"),
+             RCLASS_PRIME_CLASSEXT_READABLE_P(klass) ? "t" : "f",
+             RCLASS_PRIME_CLASSEXT_WRITABLE_P(klass) ? "t" : "f");
+    rb_str_cat_cstr(res, buf);
+
+    classext_tbl = RCLASS_CLASSEXT_TBL(klass);
+    if (!classext_tbl) {
+        rb_str_cat_cstr(res, "Non-prime classexts: 0\n");
+    }
+    else {
+        snprintf(buf, 2048, "Non-prime classexts: %zu\n", st_table_size(classext_tbl));
+        rb_str_cat_cstr(res, buf);
+    }
+
+    rb_class_classext_foreach(klass, dump_classext_i, (void *)res);
+
+    return res;
+}
+
+#endif /* RUBY_DEBUG */
+
 /*
  *  Document-class: Namespace
  *
@@ -1100,11 +970,7 @@ Init_Namespace(void)
     rb_cNamespaceEntry = rb_define_class_under(rb_cNamespace, "Entry", rb_cObject);
     rb_define_alloc_func(rb_cNamespaceEntry, rb_namespace_entry_alloc);
 
-    /* :nodoc: */
-    rb_mNamespaceRefiner = rb_define_module_under(rb_cNamespace, "Refiner");
-    if (rb_namespace_available()) {
-        setup_builtin_refinement(rb_mNamespaceRefiner);
-    }
+    initialize_root_namespace();
 
     /* :nodoc: */
     rb_mNamespaceLoader = rb_define_module_under(rb_cNamespace, "Loader");
@@ -1112,8 +978,16 @@ Init_Namespace(void)
     namespace_define_loader_method("require_relative");
     namespace_define_loader_method("load");
 
+    if (rb_namespace_available()) {
+        rb_include_module(rb_cObject, rb_mNamespaceLoader);
+
+#ifdef RUBY_DEBUG
+        rb_define_global_function("dump_classext", rb_f_dump_classext, 1);
+#endif
+    }
+
     rb_define_singleton_method(rb_cNamespace, "enabled?", rb_namespace_s_getenabled, 0);
-    rb_define_singleton_method(rb_cNamespace, "current", rb_namespace_current, 0);
+    rb_define_singleton_method(rb_cNamespace, "current", rb_namespace_s_current, 0);
     rb_define_singleton_method(rb_cNamespace, "is_builtin?", rb_namespace_s_is_builtin_p, 1);
 
     rb_define_method(rb_cNamespace, "load_path", rb_namespace_load_path, 0);
@@ -1123,7 +997,4 @@ Init_Namespace(void)
     rb_define_method(rb_cNamespace, "eval", rb_namespace_eval, 1);
 
     rb_define_method(rb_cNamespace, "inspect", rb_namespace_inspect, 0);
-
-    rb_vm_t *vm = GET_VM();
-    vm->require_stack = rb_ary_new();
 }
diff --git a/proc.c b/proc.c
index 68f63040b7..11f09439a1 100644
--- a/proc.c
+++ b/proc.c
@@ -683,7 +683,6 @@ cfunc_proc_new(VALUE klass, VALUE ifunc)
 {
     rb_proc_t *proc;
     cfunc_proc_t *sproc;
-    const rb_namespace_t *ns = rb_current_namespace();
     VALUE procval = TypedData_Make_Struct(klass, cfunc_proc_t, &proc_data_type, sproc);
     VALUE *ep;
 
@@ -698,7 +697,6 @@ cfunc_proc_new(VALUE klass, VALUE ifunc)
 
     /* self? */
     RB_OBJ_WRITE(procval, &proc->block.as.captured.code.ifunc, ifunc);
-    proc->ns = ns;
     proc->is_lambda = TRUE;
     return procval;
 }
diff --git a/ruby.c b/ruby.c
index 5a78a7c764..9ecc8f15b3 100644
--- a/ruby.c
+++ b/ruby.c
@@ -445,7 +445,7 @@ ruby_push_include(const char *path, VALUE (*filter)(VALUE))
 {
     const char sep = PATH_SEP_CHAR;
     const char *p, *s;
-    VALUE load_path = GET_VM()->load_path;
+    VALUE load_path = rb_root_namespace()->load_path;
 #ifdef __CYGWIN__
     char rubylib[FILENAME_MAX];
     VALUE buf = 0;
@@ -750,7 +750,7 @@ ruby_init_loadpath(void)
     rb_gc_register_address(&ruby_archlibdir_path);
     ruby_archlibdir_path = archlibdir;
 
-    load_path = GET_VM()->load_path;
+    load_path = rb_root_namespace()->load_path;
 
     ruby_push_include(getenv("RUBYLIB"), identical_path);
 
@@ -2324,8 +2324,8 @@ process_options(int argc, char **argv, ruby_cmdline_options_t *opt)
     char fbuf[MAXPATHLEN];
     int i = (int)proc_options(argc, argv, opt, 0);
     unsigned int dump = opt->dump & dump_exit_bits;
-    rb_vm_t *vm = GET_VM();
-    const long loaded_before_enc = RARRAY_LEN(vm->loaded_features);
+    const rb_namespace_t *ns = rb_root_namespace();
+    const long loaded_before_enc = RARRAY_LEN(ns->loaded_features);
 
     if (opt->dump & (DUMP_BIT(usage)|DUMP_BIT(help))) {
         const char *const progname =
@@ -2473,7 +2473,7 @@ process_options(int argc, char **argv, ruby_cmdline_options_t *opt)
     rb_obj_freeze(opt->script_name);
     if (IF_UTF8_PATH(uenc != lenc, 1)) {
         long i;
-        VALUE load_path = vm->load_path;
+        VALUE load_path = ns->load_path;
         const ID id_initial_load_path_mark = INITIAL_LOAD_PATH_MARK;
         int modifiable = FALSE;
 
@@ -2496,11 +2496,11 @@ process_options(int argc, char **argv, ruby_cmdline_options_t *opt)
             RARRAY_ASET(load_path, i, path);
         }
         if (modifiable) {
-            rb_ary_replace(vm->load_path_snapshot, load_path);
+            rb_ary_replace(ns->load_path_snapshot, load_path);
         }
     }
     {
-        VALUE loaded_features = vm->loaded_features;
+        VALUE loaded_features = ns->loaded_features;
         bool modified = false;
         for (long i = loaded_before_enc; i < RARRAY_LEN(loaded_features); ++i) {
             VALUE path = RARRAY_AREF(loaded_features, i);
@@ -2512,7 +2512,7 @@ process_options(int argc, char **argv, ruby_cmdline_options_t *opt)
             RARRAY_ASET(loaded_features, i, path);
         }
         if (modified) {
-            rb_ary_replace(vm->loaded_features_snapshot, loaded_features);
+            rb_ary_replace(ns->loaded_features_snapshot, loaded_features);
         }
     }
 
diff --git a/variable.c b/variable.c
index 4f0f83d203..ec3be2fda3 100644
--- a/variable.c
+++ b/variable.c
@@ -1012,6 +1012,7 @@ rb_gvar_set(ID id, VALUE val)
     RB_VM_LOCKING() {
         entry = rb_global_entry(id);
 
+        // TODO: consider root/main namespaces
         if (USE_NAMESPACE_GVAR_TBL(ns, entry)) {
             rb_hash_aset(ns->gvar_tbl, rb_id2sym(entry->id), val);
             retval = val;
@@ -3308,43 +3309,6 @@ autoload_apply_constants(VALUE _arguments)
     return Qtrue;
 }
 
-struct autoload_feature_require_data {
-    struct autoload_load_arguments *arguments;
-    VALUE receiver;
-    VALUE feature;
-};
-
-static VALUE
-autoload_feature_require_in_builtin(VALUE arg)
-{
-    struct autoload_feature_require_data *data = (struct autoload_feature_require_data *)arg;
-
-    VALUE result = rb_funcall(data->receiver, rb_intern("require"), 1, data->feature);
-    if (RTEST(result)) {
-        return rb_mutex_synchronize(autoload_mutex, autoload_apply_constants, (VALUE)data->arguments);
-    }
-    return Qnil;
-}
-
-static VALUE
-autoload_feature_require_ensure_in_builtin(VALUE _arg)
-{
-    /*
-     * The gccct should be cleared again after the rb_funcall() to remove
-     * the inconsistent cache entry against the current namespace.
-     */
-    rb_gccct_clear_table(Qnil);
-    rb_namespace_disable_builtin();
-    return Qnil;
-}
-
-static VALUE
-autoload_feature_require_in_builtin_wrap(VALUE arg)
-{
-    return rb_ensure(autoload_feature_require_in_builtin, arg,
-                     autoload_feature_require_ensure_in_builtin, Qnil);
-}
-
 static VALUE
 autoload_feature_require(VALUE _arguments)
 {
@@ -3358,26 +3322,16 @@ autoload_feature_require(VALUE _arguments)
     // We save this for later use in autoload_apply_constants:
     arguments->autoload_data = rb_check_typeddata(autoload_const->autoload_data_value, &autoload_data_type);
 
-    if (NIL_P(autoload_namespace)) {
-        rb_namespace_enable_builtin();
-        /*
-         * Clear the global cc cache table because the require method can be different from the current
-         * namespace's one and it may cause inconsistent cc-cme states.
-         * For example, the assertion below may fail in gccct_method_search();
-         * VM_ASSERT(vm_cc_check_cme(cc, rb_callable_method_entry(klass, mid)))
-         */
-        rb_gccct_clear_table(Qnil);
-        struct autoload_feature_require_data data = {
-            .arguments = arguments,
-            .receiver = receiver,
-            .feature = arguments->autoload_data->feature,
-        };
-        return rb_namespace_exec(rb_builtin_namespace(), autoload_feature_require_in_builtin_wrap, (VALUE)&data);
-    }
-
-    if (RTEST(autoload_namespace) && NAMESPACE_OPTIONAL_P(rb_get_namespace_t(autoload_namespace))) {
+    if (rb_namespace_available() && NAMESPACE_OBJ_P(autoload_namespace))
         receiver = autoload_namespace;
-    }
+
+    /*
+     * Clear the global cc cache table because the require method can be different from the current
+     * namespace's one and it may cause inconsistent cc-cme states.
+     * For example, the assertion below may fail in gccct_method_search();
+     * VM_ASSERT(vm_cc_check_cme(cc, rb_callable_method_entry(klass, mid)))
+     */
+    rb_gccct_clear_table(Qnil);
 
     VALUE result = rb_funcall(receiver, rb_intern("require"), 1, arguments->autoload_data->feature);
 
diff --git a/vm.c b/vm.c
index 479b3be94f..d93b9fe921 100644
--- a/vm.c
+++ b/vm.c
@@ -95,6 +95,29 @@ rb_vm_search_cf_from_ep(const rb_execution_context_t *ec, const rb_control_frame
     }
 }
 
+static const VALUE *
+VM_EP_RUBY_LEP(const rb_execution_context_t *ec, const rb_control_frame_t *current_cfp)
+{
+    const VALUE *ep = current_cfp->ep;
+    const rb_control_frame_t *cfp, *checkpoint_cfp = current_cfp;
+
+    while (!VM_ENV_LOCAL_P(ep) || VM_ENV_FRAME_TYPE_P(ep, VM_FRAME_MAGIC_CFUNC)) {
+        while (!VM_ENV_LOCAL_P(ep)) {
+            ep = VM_ENV_PREV_EP(ep);
+        }
+        while (VM_ENV_FRAME_TYPE_P(ep, VM_FRAME_MAGIC_CFUNC)) {
+            if (!cfp) {
+                cfp = rb_vm_search_cf_from_ep(ec, checkpoint_cfp, ep);
+            }
+            cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
+            ep = cfp->ep;
+        }
+        checkpoint_cfp = cfp;
+        cfp = NULL;
+    }
+    return ep;
+}
+
 const VALUE *
 rb_vm_ep_local_ep(const VALUE *ep)
 {
@@ -118,7 +141,15 @@ PUREFUNC(static inline VALUE VM_CF_BLOCK_HANDLER(const rb_control_frame_t * cons
 static inline VALUE
 VM_CF_BLOCK_HANDLER(const rb_control_frame_t * const cfp)
 {
-    const VALUE *ep = VM_CF_LEP(cfp);
+    const VALUE *ep;
+    if (VM_ENV_NAMESPACED_P(cfp->ep)) {
+        VM_ASSERT(VM_ENV_LOCAL_P(cfp->ep));
+        /* Never set black_handler for VM_FRAME_MAGIC_TOP or VM_FRAME_MAGIC_CLASS
+         * and the specval is used for namespace (rb_namespace_t) in these case
+         */
+        return VM_BLOCK_HANDLER_NONE;
+    }
+    ep = VM_CF_LEP(cfp);
     return VM_ENV_BLOCK_HANDLER(ep);
 }
 
@@ -761,15 +792,16 @@ vm_stat(int argc, VALUE *argv, VALUE self)
 /* control stack frame */
 
 static void
-vm_set_top_stack(rb_execution_context_t *ec, const rb_iseq_t *iseq)
+vm_set_top_stack(rb_execution_context_t *ec, const rb_iseq_t *iseq, const rb_namespace_t *ns)
 {
     if (ISEQ_BODY(iseq)->type != ISEQ_TYPE_TOP) {
         rb_raise(rb_eTypeError, "Not a toplevel InstructionSequence");
     }
 
     /* for return */
-    vm_push_frame(ec, iseq, VM_FRAME_MAGIC_TOP | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH, rb_ec_thread_ptr(ec)->top_self,
-                  VM_BLOCK_HANDLER_NONE,
+    vm_push_frame(ec, iseq, VM_FRAME_MAGIC_TOP | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH,
+                  rb_ec_thread_ptr(ec)->top_self,
+                  GC_GUARDED_PTR(ns),
                   (VALUE)vm_cref_new_toplevel(ec), /* cref or me */
                   ISEQ_BODY(iseq)->iseq_encoded, ec->cfp->sp,
                   ISEQ_BODY(iseq)->local_table_size, ISEQ_BODY(iseq)->stack_max);
@@ -976,6 +1008,7 @@ vm_make_env_each(const rb_execution_context_t * const ec, rb_control_frame_t *co
         }
     }
     else {
+        VM_ASSERT(VM_ENV_LOCAL_P(ep));
         VALUE block_handler = VM_ENV_BLOCK_HANDLER(ep);
 
         if (block_handler != VM_BLOCK_HANDLER_NONE) {
@@ -1163,7 +1196,6 @@ vm_proc_create_from_captured(VALUE klass,
 {
     VALUE procval = rb_proc_alloc(klass);
     rb_proc_t *proc = RTYPEDDATA_DATA(procval);
-    const rb_namespace_t *ns = rb_current_namespace();
 
     VM_ASSERT(VM_EP_IN_HEAP_P(GET_EC(), captured->ep));
 
@@ -1173,7 +1205,6 @@ vm_proc_create_from_captured(VALUE klass,
     rb_vm_block_ep_update(procval, &proc->block, captured->ep);
 
     vm_block_type_set(&proc->block, block_type);
-    proc->ns = ns;
     proc->is_from_method = is_from_method;
     proc->is_lambda = is_lambda;
 
@@ -1205,12 +1236,10 @@ proc_create(VALUE klass, const struct rb_block *block, int8_t is_from_method, in
 {
     VALUE procval = rb_proc_alloc(klass);
     rb_proc_t *proc = RTYPEDDATA_DATA(procval);
-    const rb_namespace_t *ns = rb_current_namespace();
 
     VM_ASSERT(VM_EP_IN_HEAP_P(GET_EC(), vm_block_ep(block)));
     rb_vm_block_copy(procval, &proc->block, block);
     vm_block_type_set(&proc->block, block->type);
-    proc->ns = ns;
     proc->is_from_method = is_from_method;
     proc->is_lambda = is_lambda;
 
@@ -2869,24 +2898,11 @@ vm_exec_handle_exception(rb_execution_context_t *ec, enum ruby_tag_type state, V
 /* misc */
 
 VALUE
-rb_iseq_eval(const rb_iseq_t *iseq)
+rb_iseq_eval(const rb_iseq_t *iseq, const rb_namespace_t *ns)
 {
     rb_execution_context_t *ec = GET_EC();
     VALUE val;
-    vm_set_top_stack(ec, iseq);
-    // TODO: set the namespace frame like require/load
-    val = vm_exec(ec);
-    return val;
-}
-
-VALUE
-rb_iseq_eval_with_refinement(const rb_iseq_t *iseq, VALUE mod)
-{
-    rb_execution_context_t *ec = GET_EC();
-    VALUE val;
-    vm_set_top_stack(ec, iseq);
-    rb_vm_using_module(mod);
-    // TODO: set the namespace frame like require/load
+    vm_set_top_stack(ec, iseq, ns);
     val = vm_exec(ec);
     return val;
 }
@@ -2896,8 +2912,7 @@ rb_iseq_eval_main(const rb_iseq_t *iseq)
 {
     rb_execution_context_t *ec = GET_EC();
     VALUE val;
-    vm_set_main_stack(ec, iseq);
-    // TODO: set the namespace frame like require/load
+    vm_set_main_stack(ec, iseq); // TODO: not need to set the namespace?
     val = vm_exec(ec);
     return val;
 }
@@ -2937,10 +2952,11 @@ rb_vm_call_cfunc(VALUE recv, VALUE (*func)(VALUE), VALUE arg,
     rb_execution_context_t *ec = GET_EC();
     const rb_control_frame_t *reg_cfp = ec->cfp;
     const rb_iseq_t *iseq = rb_iseq_new(Qnil, filename, filename, Qnil, 0, ISEQ_TYPE_TOP);
+    const rb_namespace_t *ns = rb_current_namespace();
     VALUE val;
 
     vm_push_frame(ec, iseq, VM_FRAME_MAGIC_TOP | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH,
-                  recv, block_handler,
+                  recv, GC_GUARDED_PTR(ns),
                   (VALUE)vm_cref_new_toplevel(ec), /* cref or me */
                   0, reg_cfp->sp, 0, 0);
 
@@ -2950,9 +2966,11 @@ rb_vm_call_cfunc(VALUE recv, VALUE (*func)(VALUE), VALUE arg,
     return val;
 }
 
+/* namespace */
+
 VALUE
-rb_vm_call_cfunc2(VALUE recv, VALUE (*func)(VALUE, VALUE), VALUE arg1, VALUE arg2,
-                 VALUE block_handler, VALUE filename)
+rb_vm_call_cfunc_in_namespace(VALUE recv, VALUE (*func)(VALUE, VALUE), VALUE arg1, VALUE arg2,
+                              VALUE filename, const rb_namespace_t *ns)
 {
     rb_execution_context_t *ec = GET_EC();
     const rb_control_frame_t *reg_cfp = ec->cfp;
@@ -2960,7 +2978,7 @@ rb_vm_call_cfunc2(VALUE recv, VALUE (*func)(VALUE, VALUE), VALUE arg1, VALUE arg
     VALUE val;
 
     vm_push_frame(ec, iseq, VM_FRAME_MAGIC_TOP | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH,
-                  recv, block_handler,
+                  recv, GC_GUARDED_PTR(ns),
                   (VALUE)vm_cref_new_toplevel(ec), /* cref or me */
                   0, reg_cfp->sp, 0, 0);
 
@@ -2970,6 +2988,95 @@ rb_vm_call_cfunc2(VALUE recv, VALUE (*func)(VALUE, VALUE), VALUE arg1, VALUE arg
     return val;
 }
 
+void
+rb_vm_frame_flag_set_ns_require(const rb_execution_context_t *ec)
+{
+    VM_ASSERT(rb_namespace_available());
+    VM_ENV_FLAGS_SET(ec->cfp->ep, VM_FRAME_FLAG_NS_REQUIRE);
+}
+
+static const rb_namespace_t *
+current_namespace_on_cfp(const rb_execution_context_t *ec, const rb_control_frame_t *cfp)
+{
+    rb_callable_method_entry_t *cme;
+    const rb_namespace_t *ns;
+    const VALUE *lep = VM_EP_RUBY_LEP(ec, cfp);
+    VM_ASSERT(lep);
+    VM_ASSERT(rb_namespace_available());
+
+    if (VM_ENV_FRAME_TYPE_P(lep, VM_FRAME_MAGIC_METHOD)) {
+        cme = check_method_entry(lep[VM_ENV_DATA_INDEX_ME_CREF], TRUE);
+        VM_ASSERT(cme);
+        VM_ASSERT(cme->def);
+        return cme->def->ns;
+    }
+    else if (VM_ENV_FRAME_TYPE_P(lep, VM_FRAME_MAGIC_TOP) || VM_ENV_FRAME_TYPE_P(lep, VM_FRAME_MAGIC_CLASS)) {
+        VM_ASSERT(VM_ENV_LOCAL_P(lep));
+        return VM_ENV_NAMESPACE(lep);
+    }
+    else if (VM_ENV_FRAME_TYPE_P(lep, VM_FRAME_MAGIC_DUMMY)) {
+        // No valid local ep found (just after process boot?)
+        // return the root namespace (the only valid namespace) until the main is initialized
+        ns = rb_main_namespace();
+        if (ns)
+            return ns;
+        return rb_root_namespace();
+    }
+    else {
+        rb_bug("BUG: Local ep without cme/namespace, flags: %08lX", (unsigned long)lep[VM_ENV_DATA_INDEX_FLAGS]);
+    }
+    UNREACHABLE_RETURN(0);
+}
+
+const rb_namespace_t *
+rb_vm_current_namespace(const rb_execution_context_t *ec)
+{
+    VM_ASSERT(rb_namespace_available());
+    return current_namespace_on_cfp(ec, ec->cfp);
+}
+
+static const rb_control_frame_t *
+find_loader_control_frame(const rb_execution_context_t *ec, const rb_control_frame_t *cfp, const rb_control_frame_t *end_cfp)
+{
+    while (RUBY_VM_VALID_CONTROL_FRAME_P(cfp, end_cfp)) {
+        if (!VM_ENV_FRAME_TYPE_P(cfp->ep, VM_FRAME_MAGIC_CFUNC))
+            break;
+        if (!NAMESPACE_ROOT_P(current_namespace_on_cfp(ec, cfp)))
+            break;
+        cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
+    }
+    VM_ASSERT(RUBY_VM_VALID_CONTROL_FRAME_P(cfp, end_cfp));
+    return cfp;
+}
+
+const rb_namespace_t *
+rb_vm_loading_namespace(const rb_execution_context_t *ec)
+{
+    const rb_control_frame_t *cfp, *current_cfp, *end_cfp;
+
+    if (!rb_namespace_available() || !ec)
+        return rb_root_namespace();
+
+    cfp = ec->cfp;
+    current_cfp = cfp;
+    end_cfp = RUBY_VM_END_CONTROL_FRAME(ec);
+
+    while (RUBY_VM_VALID_CONTROL_FRAME_P(cfp, end_cfp)) {
+        if (VM_ENV_FLAGS(cfp->ep, VM_FRAME_FLAG_NS_REQUIRE)) {
+            if (RTEST(cfp->self) && NAMESPACE_OBJ_P(cfp->self)) {
+                // Namespace#require, #require_relative, #load
+                return rb_get_namespace_t(cfp->self);
+            }
+            // Kernel#require, #require_relative, #load
+            cfp = find_loader_control_frame(ec, cfp, end_cfp);
+            return current_namespace_on_cfp(ec, cfp);
+        }
+        cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
+    }
+    // no require/load with explicit namespaces.
+    return current_namespace_on_cfp(ec, current_cfp);
+}
+
 /* vm */
 
 void
@@ -2980,22 +3087,13 @@ rb_vm_update_references(void *ptr)
 
         vm->self = rb_gc_location(vm->self);
         vm->mark_object_ary = rb_gc_location(vm->mark_object_ary);
-        vm->load_path = rb_gc_location(vm->load_path);
-        vm->load_path_snapshot = rb_gc_location(vm->load_path_snapshot);
-
-        if (vm->load_path_check_cache) {
-            vm->load_path_check_cache = rb_gc_location(vm->load_path_check_cache);
-        }
-
-        vm->expanded_load_path = rb_gc_location(vm->expanded_load_path);
-        vm->loaded_features = rb_gc_location(vm->loaded_features);
-        vm->loaded_features_snapshot = rb_gc_location(vm->loaded_features_snapshot);
-        vm->loaded_features_realpaths = rb_gc_location(vm->loaded_features_realpaths);
-        vm->loaded_features_realpath_map = rb_gc_location(vm->loaded_features_realpath_map);
-        vm->top_self = rb_gc_location(vm->top_self);
-        vm->require_stack = rb_gc_location(vm->require_stack);
         vm->orig_progname = rb_gc_location(vm->orig_progname);
 
+        if (vm->root_namespace)
+            rb_namespace_gc_update_references(vm->root_namespace);
+        if (vm->main_namespace)
+            rb_namespace_gc_update_references(vm->main_namespace);
+
         rb_gc_update_values(RUBY_NSIG, vm->trap_list.cmd);
 
         if (vm->coverages) {
@@ -3067,29 +3165,18 @@ rb_vm_mark(void *ptr)
 
         rb_gc_mark_movable(vm->self);
 
+        if (vm->root_namespace) {
+            rb_namespace_entry_mark(vm->root_namespace);
+        }
         if (vm->main_namespace) {
-            rb_namespace_entry_mark((void *)vm->main_namespace);
+            rb_namespace_entry_mark(vm->main_namespace);
         }
 
         rb_gc_mark_movable(vm->mark_object_ary);
-        rb_gc_mark_movable(vm->load_path);
-        rb_gc_mark_movable(vm->load_path_snapshot);
-        rb_gc_mark_movable(vm->load_path_check_cache);
-        rb_gc_mark_movable(vm->expanded_load_path);
-        rb_gc_mark_movable(vm->loaded_features);
-        rb_gc_mark_movable(vm->loaded_features_snapshot);
-        rb_gc_mark_movable(vm->loaded_features_realpaths);
-        rb_gc_mark_movable(vm->loaded_features_realpath_map);
-        rb_gc_mark_movable(vm->require_stack);
-        rb_gc_mark_movable(vm->top_self);
         rb_gc_mark_movable(vm->orig_progname);
         rb_gc_mark_movable(vm->coverages);
         rb_gc_mark_movable(vm->me2counter);
 
-        if (vm->loading_table) {
-            rb_mark_tbl(vm->loading_table);
-        }
-
         rb_gc_mark_values(RUBY_NSIG, vm->trap_list.cmd);
 
         rb_id_table_foreach_values(vm->negative_cme_table, vm_mark_negative_cme, NULL);
@@ -3124,14 +3211,6 @@ rb_vm_register_special_exception_str(enum ruby_special_exceptions sp, VALUE cls,
     rb_vm_register_global_object(exc);
 }
 
-static int
-free_loading_table_entry(st_data_t key, st_data_t value, st_data_t arg)
-{
-    xfree((char *)key);
-    return ST_DELETE;
-}
-
-void rb_free_loaded_features_index(rb_vm_t *vm);
 void rb_objspace_free_objects(void *objspace);
 
 int
@@ -3153,7 +3232,6 @@ ruby_vm_destruct(rb_vm_t *vm)
             rb_free_vm_opt_tables();
             rb_free_warning();
             rb_free_rb_global_tbl();
-            rb_free_loaded_features_index(vm);
 
             rb_id_table_free(vm->negative_cme_table);
             st_free_table(vm->overloaded_cme_table);
@@ -3184,11 +3262,6 @@ ruby_vm_destruct(rb_vm_t *vm)
 
         rb_vm_living_threads_init(vm);
         ruby_vm_run_at_exit_hooks(vm);
-        if (vm->loading_table) {
-            st_foreach(vm->loading_table, free_loading_table_entry, 0);
-            st_free_table(vm->loading_table);
-            vm->loading_table = 0;
-        }
         if (vm->ci_table) {
             st_free_table(vm->ci_table);
             vm->ci_table = NULL;
@@ -3288,8 +3361,6 @@ vm_memsize(const void *ptr)
 
     return (
         sizeof(rb_vm_t) +
-        rb_st_memsize(vm->loaded_features_index) +
-        rb_st_memsize(vm->loading_table) +
         rb_vm_memsize_postponed_job_queue() +
         rb_vm_memsize_workqueue(&vm->workqueue) +
         vm_memsize_at_exit_list(vm->at_exit) +
@@ -3558,8 +3629,6 @@ thread_mark(void *ptr)
     rb_gc_mark(th->pending_interrupt_mask_stack);
     rb_gc_mark(th->top_self);
     rb_gc_mark(th->top_wrapper);
-    rb_gc_mark(th->namespaces);
-    if (NAMESPACE_USER_P(th->ns)) rb_namespace_entry_mark(th->ns);
     if (th->root_fiber) rb_fiber_mark_self(th->root_fiber);
 
     RUBY_ASSERT(th->ec == rb_fiberptr_get_ec(th->ec->fiber_ptr));
@@ -3686,6 +3755,8 @@ rb_ec_clear_vm_stack(rb_execution_context_t *ec)
 static void
 th_init(rb_thread_t *th, VALUE self, rb_vm_t *vm)
 {
+    const rb_namespace_t *ns = rb_current_namespace();
+
     th->self = self;
 
     rb_threadptr_root_fiber_setup(th);
@@ -3707,9 +3778,12 @@ th_init(rb_thread_t *th, VALUE self, rb_vm_t *vm)
     th->status = THREAD_RUNNABLE;
     th->last_status = Qnil;
     th->top_wrapper = 0;
-    th->top_self = vm->top_self; // 0 while self == 0
-    th->namespaces = 0;
-    th->ns = 0;
+    if (ns->top_self) {
+        th->top_self = ns->top_self;
+    }
+    else {
+        th->top_self = 0;
+    }
     th->value = Qundef;
 
     th->ec->errinfo = Qnil;
@@ -3739,16 +3813,10 @@ th_init(rb_thread_t *th, VALUE self, rb_vm_t *vm)
 VALUE
 rb_thread_alloc(VALUE klass)
 {
-    rb_namespace_t *ns;
-    rb_execution_context_t *ec = GET_EC();
     VALUE self = thread_alloc(klass);
     rb_thread_t *target_th = rb_thread_ptr(self);
     target_th->ractor = GET_RACTOR();
     th_init(target_th, self, target_th->vm = GET_VM());
-    if ((ns = rb_ec_thread_ptr(ec)->ns) == 0) {
-        ns = rb_main_namespace();
-    }
-    target_th->ns = ns;
     return self;
 }
 
@@ -4295,8 +4363,6 @@ Init_VM(void)
         th->vm = vm;
         th->top_wrapper = 0;
         th->top_self = rb_vm_top_self();
-        th->namespaces = 0;
-        th->ns = 0;
 
         rb_vm_register_global_object((VALUE)iseq);
         th->ec->cfp->iseq = iseq;
@@ -4511,7 +4577,6 @@ Init_vm_objects(void)
 
     /* initialize mark object array, hash */
     vm->mark_object_ary = pin_array_list_new(Qnil);
-    vm->loading_table = st_init_strtable();
     vm->ci_table = st_init_table(&vm_ci_hashtype);
     vm->cc_refinement_table = rb_set_init_numtable();
 }
@@ -4547,17 +4612,20 @@ main_to_s(VALUE obj)
 VALUE
 rb_vm_top_self(void)
 {
-    return GET_VM()->top_self;
+    const rb_namespace_t *ns = rb_current_namespace();
+    VM_ASSERT(ns);
+    VM_ASSERT(ns->top_self);
+    return ns->top_self;
 }
 
 void
 Init_top_self(void)
 {
     rb_vm_t *vm = GET_VM();
-
-    vm->top_self = rb_obj_alloc(rb_cObject);
-    rb_define_singleton_method(rb_vm_top_self(), "to_s", main_to_s, 0);
-    rb_define_alias(rb_singleton_class(rb_vm_top_self()), "inspect", "to_s");
+    vm->root_namespace = (rb_namespace_t *)rb_root_namespace();
+    vm->root_namespace->top_self = rb_obj_alloc(rb_cObject);
+    rb_define_singleton_method(vm->root_namespace->top_self, "to_s", main_to_s, 0);
+    rb_define_alias(rb_singleton_class(vm->root_namespace->top_self), "inspect", "to_s");
 }
 
 VALUE *
diff --git a/vm_core.h b/vm_core.h
index b5a04101ab..da48976dc1 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -313,7 +313,6 @@ struct rb_calling_info {
     int argc;
     bool kw_splat;
     VALUE heap_argv;
-    const rb_namespace_t *proc_ns;
 };
 
 #ifndef VM_ARGC_STACK_MAX
@@ -751,20 +750,10 @@ typedef struct rb_vm_struct {
     const VALUE special_exceptions[ruby_special_error_count];
 
     /* namespace */
+    rb_namespace_t *root_namespace;
     rb_namespace_t *main_namespace;
 
     /* load */
-    VALUE top_self;
-    VALUE load_path;
-    VALUE load_path_snapshot;
-    VALUE load_path_check_cache;
-    VALUE expanded_load_path;
-    VALUE loaded_features;
-    VALUE loaded_features_snapshot;
-    VALUE loaded_features_realpaths;
-    VALUE loaded_features_realpath_map;
-    struct st_table *loaded_features_index;
-    struct st_table *loading_table;
     // For running the init function of statically linked
     // extensions when they are loaded
     struct st_table *static_ext_inits;
@@ -828,9 +817,6 @@ typedef struct rb_vm_struct {
         size_t fiber_vm_stack_size;
         size_t fiber_machine_stack_size;
     } default_params;
-
-    // TODO: a single require_stack can't support multi-threaded require trees
-    VALUE require_stack;
 } rb_vm_t;
 
 /* default values */
@@ -1137,9 +1123,6 @@ typedef struct rb_thread_struct {
     /* for load(true) */
     VALUE top_self;
     VALUE top_wrapper;
-    /* for namespace */
-    VALUE namespaces; // Stack of namespaces
-    rb_namespace_t *ns; // The current one
 
     /* thread control */
 
@@ -1279,7 +1262,6 @@ RUBY_SYMBOL_EXPORT_END
 
 typedef struct {
     const struct rb_block block;
-    const rb_namespace_t *ns;
     unsigned int is_from_method: 1;	/* bool */
     unsigned int is_lambda: 1;		/* bool */
     unsigned int is_isolated: 1;        /* bool */
@@ -1371,11 +1353,11 @@ typedef rb_control_frame_t *
 
 enum vm_frame_env_flags {
     /* Frame/Environment flag bits:
-     *   MMMM MMMM MMMM MMMM __FF FFFF FFFE EEEX (LSB)
+     *   MMMM MMMM MMMM MMMM ___F FFFF FFFE EEEX (LSB)
      *
      * X   : tag for GC marking (It seems as Fixnum)
      * EEE : 4 bits Env flags
-     * FF..: 9 bits Frame flags
+     * FF..: 8 bits Frame flags
      * MM..: 15 bits frame magic (to check frame corruption)
      */
 
@@ -1398,10 +1380,9 @@ enum vm_frame_env_flags {
     VM_FRAME_FLAG_CFRAME    = 0x0080,
     VM_FRAME_FLAG_LAMBDA    = 0x0100,
     VM_FRAME_FLAG_MODIFIED_BLOCK_PARAM = 0x0200,
-    VM_FRAME_FLAG_CFRAME_KW = 0x0400,
-    VM_FRAME_FLAG_PASSED    = 0x0800,
-    VM_FRAME_FLAG_NS_SWITCH = 0x1000,
-    VM_FRAME_FLAG_LOAD_ISEQ = 0x2000,
+    VM_FRAME_FLAG_CFRAME_KW  = 0x0400,
+    VM_FRAME_FLAG_PASSED     = 0x0800,
+    VM_FRAME_FLAG_NS_REQUIRE = 0x1000,
 
     /* env flag */
     VM_ENV_FLAG_LOCAL       = 0x0002,
@@ -1445,6 +1426,12 @@ VM_ENV_FLAGS(const VALUE *ep, long flag)
     return flags & flag;
 }
 
+static inline unsigned long
+VM_ENV_FRAME_TYPE_P(const VALUE *ep, unsigned long frame_type)
+{
+    return VM_ENV_FLAGS(ep, VM_FRAME_MAGIC_MASK) == frame_type;
+}
+
 static inline unsigned long
 VM_FRAME_TYPE(const rb_control_frame_t *cfp)
 {
@@ -1501,9 +1488,9 @@ VM_FRAME_RUBYFRAME_P(const rb_control_frame_t *cfp)
 }
 
 static inline int
-VM_FRAME_NS_SWITCH_P(const rb_control_frame_t *cfp)
+VM_FRAME_NS_REQUIRE_P(const rb_control_frame_t *cfp)
 {
-    return VM_ENV_FLAGS(cfp->ep, VM_FRAME_FLAG_NS_SWITCH) != 0;
+    return VM_ENV_FLAGS(cfp->ep, VM_FRAME_FLAG_NS_REQUIRE) != 0;
 }
 
 #define RUBYVM_CFUNC_FRAME_P(cfp) \
@@ -1525,13 +1512,32 @@ VM_ENV_PREV_EP(const VALUE *ep)
     return GC_GUARDED_PTR_REF(ep[VM_ENV_DATA_INDEX_SPECVAL]);
 }
 
+static inline bool
+VM_ENV_NAMESPACED_P(const VALUE *ep)
+{
+    return VM_ENV_FRAME_TYPE_P(ep, VM_FRAME_MAGIC_CLASS) || VM_ENV_FRAME_TYPE_P(ep, VM_FRAME_MAGIC_TOP);
+}
+
 static inline VALUE
 VM_ENV_BLOCK_HANDLER(const VALUE *ep)
 {
+    if (VM_ENV_NAMESPACED_P(ep)) {
+        VM_ASSERT(VM_ENV_LOCAL_P(ep));
+        return VM_BLOCK_HANDLER_NONE;
+    }
+
     VM_ASSERT(VM_ENV_LOCAL_P(ep));
     return ep[VM_ENV_DATA_INDEX_SPECVAL];
 }
 
+static inline const rb_namespace_t *
+VM_ENV_NAMESPACE(const VALUE *ep)
+{
+    VM_ASSERT(VM_ENV_NAMESPACED_P(ep));
+    VM_ASSERT(VM_ENV_LOCAL_P(ep));
+    return (const rb_namespace_t *)GC_GUARDED_PTR_REF(ep[VM_ENV_DATA_INDEX_SPECVAL]);
+}
+
 #if VM_CHECK_MODE > 0
 int rb_vm_ep_in_heap_p(const VALUE *ep);
 #endif
@@ -1852,8 +1858,7 @@ NORETURN(void rb_bug_for_fatal_signal(ruby_sighandler_t default_sighandler, int
 
 /* functions about thread/vm execution */
 RUBY_SYMBOL_EXPORT_BEGIN
-VALUE rb_iseq_eval(const rb_iseq_t *iseq);
-VALUE rb_iseq_eval_with_refinement(const rb_iseq_t *iseq, VALUE mod);
+VALUE rb_iseq_eval(const rb_iseq_t *iseq, const rb_namespace_t *ns);
 VALUE rb_iseq_eval_main(const rb_iseq_t *iseq);
 VALUE rb_iseq_path(const rb_iseq_t *iseq);
 VALUE rb_iseq_realpath(const rb_iseq_t *iseq);
diff --git a/vm_dump.c b/vm_dump.c
index 2a863ddef9..3f686bf7fa 100644
--- a/vm_dump.c
+++ b/vm_dump.c
@@ -1148,6 +1148,7 @@ rb_vm_bugreport(const void *ctx, FILE *errout)
     enum {other_runtime_info = 0};
 #endif
     const rb_vm_t *const vm = GET_VM();
+    const rb_namespace_t *ns = rb_current_namespace();
     const rb_execution_context_t *ec = rb_current_execution_context(false);
 
     if (vm && ec) {
@@ -1196,10 +1197,19 @@ rb_vm_bugreport(const void *ctx, FILE *errout)
                     LIMITED_NAME_LENGTH(name), RSTRING_PTR(name));
             kprintf("\n");
         }
-        if (vm->loaded_features) {
+        if (rb_namespace_available()) {
+            kprintf("* Namespace: enabled\n");
+            kprintf("* Current namespace id: %ld, type: %s\n",
+                    ns->ns_id,
+                    NAMESPACE_USER_P(ns) ? (NAMESPACE_MAIN_P(ns) ? "main" : "user") : "root");
+        }
+        else {
+            kprintf("* Namespace: disabled\n");
+        }
+        if (ns->loaded_features) {
             kprintf("* Loaded features:\n\n");
-            for (i=0; i<RARRAY_LEN(vm->loaded_features); i++) {
-                name = RARRAY_AREF(vm->loaded_features, i);
+            for (i=0; i<RARRAY_LEN(ns->loaded_features); i++) {
+                name = RARRAY_AREF(ns->loaded_features, i);
                 if (RB_TYPE_P(name, T_STRING)) {
                     kprintf(" %4d %.*s\n", i,
                             LIMITED_NAME_LENGTH(name), RSTRING_PTR(name));
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 3aca1bc24f..953d6e64ab 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -5161,20 +5161,6 @@ block_proc_is_lambda(const VALUE procval)
     }
 }
 
-static inline const rb_namespace_t *
-block_proc_namespace(const VALUE procval)
-{
-    rb_proc_t *proc;
-
-    if (procval) {
-        GetProcPtr(procval, proc);
-        return proc->ns;
-    }
-    else {
-        return NULL;
-    }
-}
-
 static VALUE
 vm_yield_with_cfunc(rb_execution_context_t *ec,
                     const struct rb_captured_block *captured,
@@ -5330,10 +5316,6 @@ vm_invoke_iseq_block(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp,
 
     SET_SP(rsp);
 
-    if (calling->proc_ns) {
-        frame_flag |= VM_FRAME_FLAG_NS_SWITCH;
-    }
-
     vm_push_frame(ec, iseq,
                   frame_flag,
                   captured->self,
@@ -5434,9 +5416,6 @@ vm_invoke_proc_block(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp,
 {
     while (vm_block_handler_type(block_handler) == block_handler_type_proc) {
         VALUE proc = VM_BH_TO_PROC(block_handler);
-        if (!calling->proc_ns) {
-            calling->proc_ns = block_proc_namespace(proc);
-        }
         is_lambda = block_proc_is_lambda(proc);
         block_handler = vm_proc_to_block_handler(proc);
     }
diff --git a/vm_insnhelper.h b/vm_insnhelper.h
index 24bfbb8210..2fdd08bc6e 100644
--- a/vm_insnhelper.h
+++ b/vm_insnhelper.h
@@ -144,7 +144,7 @@ CC_SET_FASTPATH(const struct rb_callcache *cc, vm_call_handler func, bool enable
     }
 }
 
-#define GET_BLOCK_HANDLER() (GET_LEP()[VM_ENV_DATA_INDEX_SPECVAL])
+#define GET_BLOCK_HANDLER() VM_ENV_BLOCK_HANDLER(VM_EP_LEP(GET_EP()))
 
 /**********************************************************/
 /* deal with control flow 3: exception                    */
diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index b8b15adc8b..7b52774843 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -6647,6 +6647,7 @@ fn jit_rb_f_block_given_p(
     true
 }
 
+/// Codegen for `block_given?` and `defined?(yield)`
 fn gen_block_given(
     jit: &mut JITState,
     asm: &mut Assembler,
@@ -6656,15 +6657,24 @@ fn gen_block_given(
 ) {
     asm_comment!(asm, "block_given?");
 
-    // Same as rb_vm_frame_block_handler
+    // VM_ENV_FLAGS(ep, VM_FRAME_MAGIC_MASK)
     let ep_opnd = gen_get_lep(jit, asm);
-    let block_handler = asm.load(
-        Opnd::mem(64, ep_opnd, SIZEOF_VALUE_I32 * VM_ENV_DATA_INDEX_SPECVAL)
-    );
+    let flags = Opnd::mem(64, ep_opnd, VM_ENV_DATA_INDEX_FLAGS as i32 * SIZEOF_VALUE_I32);
+    let frame_type = asm.and(flags, VM_FRAME_MAGIC_MASK.into());
+
+    // Return false_opnd if VM_ENV_NAMESPACED_P(ep)
+    asm.cmp(frame_type, VM_FRAME_MAGIC_CLASS.into());
+    let block_given = asm.csel_ne(true_opnd, false_opnd);
+    asm.cmp(frame_type, VM_FRAME_MAGIC_TOP.into());
+    let block_given = asm.csel_ne(block_given, false_opnd);
+
+    // VM_ENV_BLOCK_HANDLER(VM_CF_LEP(cfp))
+    let ep_opnd = gen_get_lep(jit, asm); // Reload ep_opnd to avoid register spill
+    let block_handler = Opnd::mem(64, ep_opnd, VM_ENV_DATA_INDEX_SPECVAL * SIZEOF_VALUE_I32);
 
     // Return `block_handler != VM_BLOCK_HANDLER_NONE`
     asm.cmp(block_handler, VM_BLOCK_HANDLER_NONE.into());
-    let block_given = asm.csel_ne(true_opnd, false_opnd);
+    let block_given = asm.csel_ne(block_given, false_opnd);
     asm.mov(out_opnd, block_given);
 }
 
diff --git a/yjit/src/cruby_bindings.inc.rs b/yjit/src/cruby_bindings.inc.rs
index c8a58f424e..bb11fc42f0 100644
--- a/yjit/src/cruby_bindings.inc.rs
+++ b/yjit/src/cruby_bindings.inc.rs
@@ -259,33 +259,6 @@ pub const RSTRING_FSTR: ruby_rstring_flags = 536870912;
 pub type ruby_rstring_flags = u32;
 pub type st_data_t = ::std::os::raw::c_ulong;
 pub type st_index_t = st_data_t;
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct st_hash_type {
-    pub compare: ::std::option::Option<
-        unsafe extern "C" fn(arg1: st_data_t, arg2: st_data_t) -> ::std::os::raw::c_int,
-    >,
-    pub hash: ::std::option::Option<unsafe extern "C" fn(arg1: st_data_t) -> st_index_t>,
-}
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct st_table_entry {
-    _unused: [u8; 0],
-}
-#[repr(C)]
-#[derive(Debug, Copy, Clone)]
-pub struct st_table {
-    pub entry_power: ::std::os::raw::c_uchar,
-    pub bin_power: ::std::os::raw::c_uchar,
-    pub size_ind: ::std::os::raw::c_uchar,
-    pub rebuilds_num: ::std::os::raw::c_uint,
-    pub type_: *const st_hash_type,
-    pub num_entries: st_index_t,
-    pub bins: *mut st_index_t,
-    pub entries_start: st_index_t,
-    pub entries_bound: st_index_t,
-    pub entries: *mut st_table_entry,
-}
 pub const ST_CONTINUE: st_retval = 0;
 pub const ST_STOP: st_retval = 1;
 pub const ST_DELETE: st_retval = 2;
@@ -373,28 +346,6 @@ pub const BOP_PACK: ruby_basic_operators = 32;
 pub const BOP_INCLUDE_P: ruby_basic_operators = 33;
 pub const BOP_LAST_: ruby_basic_operators = 34;
 pub type ruby_basic_operators = u32;
-#[repr(C)]
-pub struct rb_namespace_struct {
-    pub ns_object: VALUE,
-    pub ns_id: ::std::os::raw::c_long,
-    pub top_self: VALUE,
-    pub load_path: VALUE,
-    pub load_path_snapshot: VALUE,
-    pub load_path_check_cache: VALUE,
-    pub expanded_load_path: VALUE,
-    pub loaded_features: VALUE,
-    pub loaded_features_snapshot: VALUE,
-    pub loaded_features_realpaths: VALUE,
-    pub loaded_features_realpath_map: VALUE,
-    pub loaded_features_index: *mut st_table,
-    pub loading_table: *mut st_table,
-    pub ruby_dln_libmap: VALUE,
-    pub gvar_tbl: VALUE,
-    pub is_builtin: bool,
-    pub is_user: bool,
-    pub is_optional: bool,
-}
-pub type rb_namespace_t = rb_namespace_struct;
 pub type rb_serial_t = ::std::os::raw::c_ulonglong;
 pub const imemo_env: imemo_type = 0;
 pub const imemo_cref: imemo_type = 1;
@@ -582,7 +533,6 @@ pub type rb_control_frame_t = rb_control_frame_struct;
 #[repr(C)]
 pub struct rb_proc_t {
     pub block: rb_block,
-    pub ns: *const rb_namespace_t,
     pub _bitfield_align_1: [u8; 0],
     pub _bitfield_1: __BindgenBitfieldUnit<[u8; 1usize]>,
     pub __bindgen_padding_0: [u8; 7usize],
@@ -678,8 +628,7 @@ pub const VM_FRAME_FLAG_LAMBDA: vm_frame_env_flags = 256;
 pub const VM_FRAME_FLAG_MODIFIED_BLOCK_PARAM: vm_frame_env_flags = 512;
 pub const VM_FRAME_FLAG_CFRAME_KW: vm_frame_env_flags = 1024;
 pub const VM_FRAME_FLAG_PASSED: vm_frame_env_flags = 2048;
-pub const VM_FRAME_FLAG_NS_SWITCH: vm_frame_env_flags = 4096;
-pub const VM_FRAME_FLAG_LOAD_ISEQ: vm_frame_env_flags = 8192;
+pub const VM_FRAME_FLAG_NS_REQUIRE: vm_frame_env_flags = 4096;
 pub const VM_ENV_FLAG_LOCAL: vm_frame_env_flags = 2;
 pub const VM_ENV_FLAG_ESCAPED: vm_frame_env_flags = 4;
 pub const VM_ENV_FLAG_WB_REQUIRED: vm_frame_env_flags = 8;
diff --git a/zjit/src/cruby_bindings.inc.rs b/zjit/src/cruby_bindings.inc.rs
index 5c939fabe7..1a167a83a9 100644
--- a/zjit/src/cruby_bindings.inc.rs
+++ b/zjit/src/cruby_bindings.inc.rs
@@ -386,8 +386,7 @@ pub const VM_FRAME_FLAG_LAMBDA: vm_frame_env_flags = 256;
 pub const VM_FRAME_FLAG_MODIFIED_BLOCK_PARAM: vm_frame_env_flags = 512;
 pub const VM_FRAME_FLAG_CFRAME_KW: vm_frame_env_flags = 1024;
 pub const VM_FRAME_FLAG_PASSED: vm_frame_env_flags = 2048;
-pub const VM_FRAME_FLAG_NS_SWITCH: vm_frame_env_flags = 4096;
-pub const VM_FRAME_FLAG_LOAD_ISEQ: vm_frame_env_flags = 8192;
+pub const VM_FRAME_FLAG_NS_REQUIRE: vm_frame_env_flags = 4096;
 pub const VM_ENV_FLAG_LOCAL: vm_frame_env_flags = 2;
 pub const VM_ENV_FLAG_ESCAPED: vm_frame_env_flags = 4;
 pub const VM_ENV_FLAG_WB_REQUIRED: vm_frame_env_flags = 8;