diff --git a/CHANGELOG.md b/CHANGELOG.md
index d78e270..fe95d9f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,7 @@
 
 ### Breaking Changes
 
-* Child processes now scrub inherited release boot variables and release PATH entries when `RELEASE_ROOT` is set. Set `release_env: :inherit` to opt out. Explicit `Config.env` values apply after the scrub, with release entries still removed from an explicit PATH.
+* Child processes now scrub inherited release boot variables and release PATH entries when `RELEASE_ROOT` is set. Set `release_env: :inherit` to opt out. Explicit `Config.env` values apply after the scrub, with release entries still removed from an explicit PATH. Custom runners must honor `{name, false}` entries in `opts[:env]` by removing those variables from the inherited environment on every implemented execution callback.
 * Prompt commands now pass `-` in argv and deliver prompt bytes through stdin by default. Custom runners must deliver `opts[:stdin]` and EOF, or callers must select `prompt_input: :argv`.
 
 ### Features
diff --git a/lib/codex_wrapper/iex.ex b/lib/codex_wrapper/iex.ex
index 9b181b8..017d0eb 100644
--- a/lib/codex_wrapper/iex.ex
+++ b/lib/codex_wrapper/iex.ex
@@ -45,7 +45,8 @@ defmodule CodexWrapper.IEx do
   Start a new conversation. Prints the response.
 
   Accepts all options from `CodexWrapper.exec/2` -- config options
-  (`:working_dir`, `:binary`, `:env`, `:timeout`, and `:verbose`, where only `false` is supported)
+  (`:working_dir`, `:binary`, `:env`, `:release_env`, `:timeout`, and `:verbose`,
+  where only `false` is supported)
   and exec options (`:model`, `:sandbox`, `:approval_policy`, etc.).
   """
   def chat(prompt, opts \\ []) do
@@ -210,7 +211,7 @@ defmodule CodexWrapper.IEx do
     IO.puts("\e[33m(#{turns} turn#{plural(turns)})\e[0m")
   end
 
-  @config_keys [:binary, :working_dir, :env, :timeout, :verbose]
+  @config_keys [:binary, :working_dir, :env, :release_env, :timeout, :verbose]
 
   defp split_opts(opts) do
     Enum.split_with(opts, fn {k, _v} -> k in @config_keys end)
diff --git a/lib/codex_wrapper/runner.ex b/lib/codex_wrapper/runner.ex
index c64e3e9..8bb1fe8 100644
--- a/lib/codex_wrapper/runner.ex
+++ b/lib/codex_wrapper/runner.ex
@@ -78,7 +78,9 @@ defmodule CodexWrapper.Runner do
   Execution options, as produced by `CodexWrapper.Config.cmd_opts/1`:
 
     * `:cd` -- working directory (string)
-    * `:env` -- list of `{name, value}` string tuples
+    * `:env` -- list of `{String.t(), String.t() | false}` tuples. A `false`
+      value removes an inherited variable. Custom runners must honor these
+      removals on every implemented execution callback.
     * `:stderr_to_stdout` -- merge stderr into stdout
     * `:stdin` -- complete prompt bytes, delivered before EOF. This key is
       absent when the command has no input. Custom runners must support it
diff --git a/test/codex_wrapper/iex_test.exs b/test/codex_wrapper/iex_test.exs
index e17bc40..15ec90c 100644
--- a/test/codex_wrapper/iex_test.exs
+++ b/test/codex_wrapper/iex_test.exs
@@ -1,6 +1,8 @@
 defmodule CodexWrapper.IExTest do
   use ExUnit.Case, async: false
 
+  import ExUnit.CaptureIO
+
   alias CodexWrapper.IEx, as: CIEx
 
   setup do
@@ -69,4 +71,99 @@ defmodule CodexWrapper.IExTest do
       assert {:last, 0} in CIEx.__info__(:functions)
     end
   end
+
+  describe "release_env" do
+    @describetag :tmp_dir
+
+    setup %{tmp_dir: directory} do
+      parent = %{
+        "RELEASE_ROOT" => "/release/iex-test",
+        "RELEASE_COOKIE" => "iex-cookie",
+        "ROOTDIR" => "/release/iex-test",
+        "BINDIR" => "/release/iex-test/erts-17/bin",
+        "PATH" => "/release/iex-test/bin:/release/iex-test/erts-17/bin:/usr/bin:/bin"
+      }
+
+      previous = Map.new(parent, fn {key, _value} -> {key, System.get_env(key)} end)
+
+      on_exit(fn ->
+        Enum.each(previous, fn
+          {key, nil} -> System.delete_env(key)
+          {key, value} -> System.put_env(key, value)
+        end)
+      end)
+
+      System.put_env(parent)
+
+      binary = Path.join(directory, "fake_codex")
+      report = Path.join(directory, "child-env")
+
+      report_commands =
+        Enum.map_join(parent, "\n", fn {key, _value} ->
+          ~s(printf '%s\\n' "#{key}=${#{key}-<unset>}")
+        end)
+
+      File.write!(binary, """
+      #!/bin/sh
+      {
+      #{report_commands}
+      } > "$CXW_ENV_REPORT"
+      printf '%s\\n' '{"type":"thread.started","thread_id":"iex-release-probe"}'
+      printf '%s\\n' '{"type":"turn.completed","usage":{}}'
+      """)
+
+      File.chmod!(binary, 0o755)
+
+      opts = [binary: binary, timeout: 10_000, env: [{"CXW_ENV_REPORT", report}]]
+      %{opts: opts, report: report, parent: parent}
+    end
+
+    for policy <- [:inherit, :scrub] do
+      @policy policy
+
+      test "chat/2 retains #{@policy} for later say/2 calls", context do
+        capture_io(fn ->
+          opts = Keyword.put(context.opts, :release_env, @policy)
+          assert CIEx.chat("hello", opts) == :ok
+          assert_release_env(context, @policy)
+
+          assert CIEx.say("next") == :ok
+          assert_release_env(context, @policy)
+        end)
+      end
+
+      test "resume/2 retains #{@policy} for later say/2 calls", context do
+        capture_io(fn ->
+          opts = Keyword.put(context.opts, :release_env, @policy)
+          assert CIEx.resume("iex-release-probe", opts) == :ok
+
+          for prompt <- ["hello", "next"] do
+            assert CIEx.say(prompt) == :ok
+            assert_release_env(context, @policy)
+          end
+        end)
+      end
+    end
+  end
+
+  defp assert_release_env(context, policy) do
+    actual =
+      context.report
+      |> File.read!()
+      |> String.split("\n", trim: true)
+      |> Map.new(fn line ->
+        [key, value] = String.split(line, "=", parts: 2)
+        {key, value}
+      end)
+
+    expected =
+      case policy do
+        :inherit -> context.parent
+        :scrub -> Map.new(context.parent, fn {key, _value} -> {key, "<unset>"} end)
+      end
+
+    expected = if policy == :scrub, do: Map.put(expected, "PATH", "/usr/bin:/bin"), else: expected
+    assert actual == expected
+    File.rm!(context.report)
+  end
 end