diff --git a/lib/bundler.rb b/lib/bundler.rb
index a4f6671e91..904dcb8467 100644
--- a/lib/bundler.rb
+++ b/lib/bundler.rb
@@ -567,7 +567,7 @@ module Bundler
     end
 
     def feature_flag
-      @feature_flag ||= FeatureFlag.new(VERSION)
+      @feature_flag ||= FeatureFlag.new(settings[:simulate_version] || VERSION)
     end
 
     def reset!
diff --git a/lib/bundler/environment_preserver.rb b/lib/bundler/environment_preserver.rb
index ffffceb487..444ab6fd37 100644
--- a/lib/bundler/environment_preserver.rb
+++ b/lib/bundler/environment_preserver.rb
@@ -6,7 +6,6 @@ module Bundler
     BUNDLER_KEYS = %w[
       BUNDLE_BIN_PATH
       BUNDLE_GEMFILE
-      BUNDLER_4_MODE
       BUNDLER_VERSION
       BUNDLER_SETUP
       GEM_HOME
diff --git a/lib/bundler/feature_flag.rb b/lib/bundler/feature_flag.rb
index 2267dc3ee0..34e4bcf495 100644
--- a/lib/bundler/feature_flag.rb
+++ b/lib/bundler/feature_flag.rb
@@ -50,6 +50,8 @@ module Bundler
       @major_version >= target_major_version
     end
 
+    attr_reader :bundler_version
+
     def initialize(bundler_version)
       @bundler_version = Gem::Version.create(bundler_version)
       @major_version = @bundler_version.segments.first
diff --git a/lib/bundler/self_manager.rb b/lib/bundler/self_manager.rb
index c2f54052d8..7db6c9f6f1 100644
--- a/lib/bundler/self_manager.rb
+++ b/lib/bundler/self_manager.rb
@@ -98,7 +98,6 @@ module Bundler
 
     def autoswitching_applies?
       ENV["BUNDLER_VERSION"].nil? &&
-        ENV["BUNDLER_4_MODE"].nil? &&
         ruby_can_restart_with_same_arguments? &&
         lockfile_version
     end
diff --git a/lib/bundler/version.rb b/lib/bundler/version.rb
index 5e4fb17bfb..7a8fb214c7 100644
--- a/lib/bundler/version.rb
+++ b/lib/bundler/version.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: false
 
 module Bundler
-  VERSION = (ENV["BUNDLER_4_MODE"] == "true" ? "4.0.0" : "2.7.0.dev").freeze
+  VERSION = "2.7.0.dev".freeze
 
   def self.bundler_major_version
     @bundler_major_version ||= gem_version.segments.first
diff --git a/spec/bundler/bundler/settings_spec.rb b/spec/bundler/bundler/settings_spec.rb
index 592db81e9b..c3d8533eab 100644
--- a/spec/bundler/bundler/settings_spec.rb
+++ b/spec/bundler/bundler/settings_spec.rb
@@ -333,7 +333,7 @@ that would suck --ehhh=oh geez it looks like i might have broken bundler somehow
       C
 
       expect(Bundler.ui).not_to receive(:warn)
-      expect(settings.all).to be_empty
+      expect(settings.all).to eq(simulated_version ? ["simulate_version"] : [])
     end
 
     it "converts older keys with dashes" do
diff --git a/spec/bundler/commands/config_spec.rb b/spec/bundler/commands/config_spec.rb
index 1392b17315..6840e2b04a 100644
--- a/spec/bundler/commands/config_spec.rb
+++ b/spec/bundler/commands/config_spec.rb
@@ -453,7 +453,7 @@ E
     it "does not make bundler crash and ignores the configuration" do
       bundle "config list --parseable"
 
-      expect(out).to be_empty
+      expect(out).to eq(simulated_version ? "simulate_version=#{simulated_version}" : "")
       expect(err).to be_empty
 
       ruby(<<~RUBY)
@@ -476,26 +476,38 @@ E
   describe "subcommands" do
     it "list" do
       bundle "config list", env: { "BUNDLE_FOO" => "bar" }
-      expect(out).to eq "Settings are listed in order of priority. The top value will be used.\nfoo\nSet via BUNDLE_FOO: \"bar\""
+      expected = "Settings are listed in order of priority. The top value will be used.\nfoo\nSet via BUNDLE_FOO: \"bar\""
+      expected += "\n\nsimulate_version\nSet via BUNDLE_SIMULATE_VERSION: \"#{simulated_version}\"" if simulated_version
+      expect(out).to eq(expected)
 
       bundle "config list", env: { "BUNDLE_FOO" => "bar" }, parseable: true
-      expect(out).to eq "foo=bar"
+      expected = "foo=bar"
+      expected += "\nsimulate_version=#{simulated_version}" if simulated_version
+      expect(out).to eq(expected)
     end
 
     it "list with credentials" do
       bundle "config list", env: { "BUNDLE_GEMS__MYSERVER__COM" => "user:password" }
-      expect(out).to eq "Settings are listed in order of priority. The top value will be used.\ngems.myserver.com\nSet via BUNDLE_GEMS__MYSERVER__COM: \"user:[REDACTED]\""
+      expected = "Settings are listed in order of priority. The top value will be used.\ngems.myserver.com\nSet via BUNDLE_GEMS__MYSERVER__COM: \"user:[REDACTED]\""
+      expected += "\n\nsimulate_version\nSet via BUNDLE_SIMULATE_VERSION: \"#{simulated_version}\"" if simulated_version
+      expect(out).to eq(expected)
 
       bundle "config list", parseable: true, env: { "BUNDLE_GEMS__MYSERVER__COM" => "user:password" }
-      expect(out).to eq "gems.myserver.com=user:password"
+      expected = "gems.myserver.com=user:password"
+      expected += "\nsimulate_version=#{simulated_version}" if simulated_version
+      expect(out).to eq(expected)
     end
 
     it "list with API token credentials" do
       bundle "config list", env: { "BUNDLE_GEMS__MYSERVER__COM" => "api_token:x-oauth-basic" }
-      expect(out).to eq "Settings are listed in order of priority. The top value will be used.\ngems.myserver.com\nSet via BUNDLE_GEMS__MYSERVER__COM: \"[REDACTED]:x-oauth-basic\""
+      expected = "Settings are listed in order of priority. The top value will be used.\ngems.myserver.com\nSet via BUNDLE_GEMS__MYSERVER__COM: \"[REDACTED]:x-oauth-basic\""
+      expected += "\n\nsimulate_version\nSet via BUNDLE_SIMULATE_VERSION: \"#{simulated_version}\"" if simulated_version
+      expect(out).to eq(expected)
 
       bundle "config list", parseable: true, env: { "BUNDLE_GEMS__MYSERVER__COM" => "api_token:x-oauth-basic" }
-      expect(out).to eq "gems.myserver.com=api_token:x-oauth-basic"
+      expected = "gems.myserver.com=api_token:x-oauth-basic"
+      expected += "\nsimulate_version=#{simulated_version}" if simulated_version
+      expect(out).to eq(expected)
     end
 
     it "get" do
diff --git a/spec/bundler/lock/lockfile_spec.rb b/spec/bundler/lock/lockfile_spec.rb
index 5c1ce3ca0f..e1fbe6934a 100644
--- a/spec/bundler/lock/lockfile_spec.rb
+++ b/spec/bundler/lock/lockfile_spec.rb
@@ -109,7 +109,7 @@ RSpec.describe "the lockfile format" do
          #{version}
     L
 
-    install_gemfile <<-G, verbose: true, env: { "BUNDLER_4_MODE" => nil }
+    install_gemfile <<-G, verbose: true
       source "https://gem.repo4"
 
       gem "myrack"
diff --git a/spec/bundler/realworld/slow_perf_spec.rb b/spec/bundler/realworld/slow_perf_spec.rb
index d9d1aef81c..5b74b9ea9e 100644
--- a/spec/bundler/realworld/slow_perf_spec.rb
+++ b/spec/bundler/realworld/slow_perf_spec.rb
@@ -131,14 +131,8 @@ RSpec.describe "bundle install with complex dependencies", realworld: true do
       end
     G
 
-    if Bundler.feature_flag.bundler_4_mode?
-      bundle "lock", env: { "DEBUG_RESOLVER" => "1" }, raise_on_error: false
+    bundle "lock", env: { "DEBUG_RESOLVER" => "1" }
 
-      expect(out).to include("backtracking").exactly(26).times
-    else
-      bundle "lock", env: { "DEBUG_RESOLVER" => "1" }
-
-      expect(out).to include("Solution found after 10 attempts")
-    end
+    expect(out).to include("Solution found after 10 attempts")
   end
 end
diff --git a/spec/bundler/runtime/self_management_spec.rb b/spec/bundler/runtime/self_management_spec.rb
index 880bdaface..2cb2d0175f 100644
--- a/spec/bundler/runtime/self_management_spec.rb
+++ b/spec/bundler/runtime/self_management_spec.rb
@@ -10,7 +10,7 @@ RSpec.describe "Self management" do
       "9.4.0"
     end
 
-    around do |example|
+    before do
       build_repo4 do
         build_bundler previous_minor
 
@@ -26,8 +26,6 @@ RSpec.describe "Self management" do
       G
 
       pristine_system_gems "bundler-#{current_version}"
-
-      with_env_vars("BUNDLER_4_MODE" => nil, &example)
     end
 
     it "installs locked version when using system path and uses it" do
diff --git a/spec/bundler/support/env.rb b/spec/bundler/support/env.rb
index 0899bd82a3..a198757f30 100644
--- a/spec/bundler/support/env.rb
+++ b/spec/bundler/support/env.rb
@@ -9,5 +9,9 @@ module Spec
     def rubylib
       ENV["RUBYLIB"].to_s.split(File::PATH_SEPARATOR)
     end
+
+    def simulated_version
+      ENV["BUNDLE_SIMULATE_VERSION"]
+    end
   end
 end
diff --git a/spec/bundler/support/filters.rb b/spec/bundler/support/filters.rb
index 663b7fa44b..a20b950fc7 100644
--- a/spec/bundler/support/filters.rb
+++ b/spec/bundler/support/filters.rb
@@ -1,9 +1,8 @@
 # frozen_string_literal: true
 
 class RequirementChecker < Proc
-  def self.against(present, major_only: false)
-    present = present.split(".")[0] if major_only
-    provided = Gem::Version.new(present)
+  def self.against(provided, major_only: false)
+    provided = Gem::Version.new(provided.segments.first) if major_only
 
     new do |required|
       requirement = Gem::Requirement.new(required)
@@ -28,8 +27,8 @@ end
 RSpec.configure do |config|
   config.filter_run_excluding realworld: true
 
-  config.filter_run_excluding bundler: RequirementChecker.against(Bundler::VERSION, major_only: true)
-  config.filter_run_excluding rubygems: RequirementChecker.against(Gem::VERSION)
+  config.filter_run_excluding bundler: RequirementChecker.against(Bundler.feature_flag.bundler_version, major_only: true)
+  config.filter_run_excluding rubygems: RequirementChecker.against(Gem.rubygems_version)
   config.filter_run_excluding ruby_repo: !ENV["GEM_COMMAND"].nil?
   config.filter_run_excluding no_color_tty: Gem.win_platform? || !ENV["GITHUB_ACTION"].nil?
   config.filter_run_excluding permissions: Gem.win_platform?