diff --git a/doc/COMMAND_LINE_OPTIONS.md b/doc/COMMAND_LINE_OPTIONS.md
index 08077ff1b..f4203ff1e 100644
--- a/doc/COMMAND_LINE_OPTIONS.md
+++ b/doc/COMMAND_LINE_OPTIONS.md
@@ -21,7 +21,7 @@ These are the IRB command-line options, with links to explanatory text:
 - `--colorize`: Use {color-highlighting}[rdoc-ref:IRB@Color+Highlighting]
   for input and output.
 - `--context-mode _n_`: Select method to create Binding object
-  for new {workspace}[rdoc-ref:IRB@Commands]; `n` in range `0..4`.
+  for new {workspace}[rdoc-ref:IRB@Commands]; `n` in range `0..5`.
 - `--echo`: Print ({echo}[rdoc-ref:IRB@Return-Value+Printing+-28Echoing-29])
   return values.
 - `--extra-doc-dir _dirpath_`:
diff --git a/doc/irb/irb.rd.ja b/doc/irb/irb.rd.ja
index c51e0bd60..0733a276b 100644
--- a/doc/irb/irb.rd.ja
+++ b/doc/irb/irb.rd.ja
@@ -48,7 +48,7 @@ irbの使い方は, Rubyさえ知っていればいたって簡単です. 基本
   -w                ruby -w と同じ.
   -W[level=2]       ruby -W と同じ.
   --context-mode n  新しいワークスペースを作成した時に関連する Binding
-		    オブジェクトの作成方法を 0 から 3 のいずれかに設定する.
+		    オブジェクトの作成方法を 0 から 5 のいずれかに設定する.
   --echo	    実行結果を表示する(デフォルト).
   --noecho	    実行結果を表示しない.
   --echo-on-assignment
diff --git a/lib/irb/lc/help-message b/lib/irb/lc/help-message
index 37347306e..94a27cdf0 100644
--- a/lib/irb/lc/help-message
+++ b/lib/irb/lc/help-message
@@ -9,7 +9,7 @@ Usage:  irb.rb [options] [programfile] [arguments]
   -w                Suppress warnings (same as 'ruby -w').
   -W[level=2]       Set warning level: 0=silence, 1=medium, 2=verbose
                     (same as 'ruby -W').
-  --context-mode n  Set n[0-4] to method to create Binding Object,
+  --context-mode n  Set n[0-5] to method to create Binding Object,
                     when new workspace was created.
   --extra-doc-dir   Add an extra doc dir for the doc dialog.
   --echo            Show result (default).
diff --git a/lib/irb/lc/ja/help-message b/lib/irb/lc/ja/help-message
index 844c67bbb..c703ea2c8 100644
--- a/lib/irb/lc/ja/help-message
+++ b/lib/irb/lc/ja/help-message
@@ -8,7 +8,7 @@ Usage:  irb.rb [options] [programfile] [arguments]
   -w                ruby -w と同じ.
   -W[level=2]       ruby -W と同じ.
   --context-mode n  新しいワークスペースを作成した時に関連する Binding
-		    オブジェクトの作成方法を 0 から 4 のいずれかに設定する.
+		    オブジェクトの作成方法を 0 から 5 のいずれかに設定する.
   --extra-doc-dir   指定したディレクトリのドキュメントを追加で読み込む.
   --echo	    実行結果を表示する(デフォルト).
   --noecho	    実行結果を表示しない.
diff --git a/lib/irb/workspace.rb b/lib/irb/workspace.rb
index ced9d7866..9fef8f86a 100644
--- a/lib/irb/workspace.rb
+++ b/lib/irb/workspace.rb
@@ -55,6 +55,15 @@ def initialize(*main)
           # Note that this will typically be IRB::TOPLEVEL_BINDING
           # This is to avoid RubyGems' local variables (see issue #17623)
           @binding = TOPLEVEL_BINDING.dup
+
+        when 5  # binding in Ruby::Box
+          unless defined?(Ruby::Box)
+            puts 'Context-mode 5 (binding in Ruby::Box) requires Ruby 4.0 or later.'
+            raise NameError, 'Ruby::Box not defined'
+          end
+
+          puts 'Context-mode 5 (binding in Ruby::Box) is experimental. It may be removed or changed without notice.'
+          @binding = Ruby::Box.new.eval('Kernel.binding')
         end
       end
 
diff --git a/test/irb/helper.rb b/test/irb/helper.rb
index 6a0183104..ead934a45 100644
--- a/test/irb/helper.rb
+++ b/test/irb/helper.rb
@@ -139,7 +139,7 @@ def teardown
       end
     end
 
-    def run_ruby_file(&block)
+    def run_ruby_file(timeout: TIMEOUT_SEC, &block)
       cmd = [EnvUtil.rubybin, "-I", LIB, @ruby_file.to_path]
       tmp_dir = Dir.mktmpdir
 
@@ -156,7 +156,7 @@ def run_ruby_file(&block)
       envs_for_spawn = @envs.merge('TERM' => 'dumb', 'TEST_IRB_FORCE_INTERACTIVE' => 'true')
 
       PTY.spawn(envs_for_spawn, *cmd) do |read, write, pid|
-        Timeout.timeout(TIMEOUT_SEC) do
+        Timeout.timeout(timeout) do
           while line = safe_gets(read)
             lines << line
 
diff --git a/test/irb/test_irb.rb b/test/irb/test_irb.rb
index 30f3ad5a0..1b0290d0c 100644
--- a/test/irb/test_irb.rb
+++ b/test/irb/test_irb.rb
@@ -963,4 +963,34 @@ def bar
       end
     end
   end
+
+  class ContextModeTest < TestIRB::IntegrationTestCase
+    # RUBY_BOX=1 may need more time to start IRB
+    TIMEOUT_SEC = TestIRB::IntegrationTestCase::TIMEOUT_SEC + 5
+
+    def test_context_mode_ruby_box
+      omit if RUBY_VERSION < "4.0.0"
+      @envs['RUBY_BOX'] = '1'
+
+      write_rc <<~'RUBY'
+        IRB.conf[:CONTEXT_MODE] = 5
+      RUBY
+
+      write_ruby <<~'RUBY'
+        require 'irb'
+        puts 'binding.irb' # Mark for breakpoint trigger
+        IRB.start
+        p answer2: 1 + 2
+      RUBY
+
+      output = run_ruby_file(timeout: TIMEOUT_SEC) do
+        type 'class Integer; def +(_other) = 42; end'
+        type 'p answer1: 1 + 2'
+        type 'exit'
+      end
+
+      assert_include(output, '{answer1: 42}')
+      assert_include(output, '{answer2: 3}')
+    end
+  end
 end