diff --git a/README.md b/README.md
index f11d009..c58ee8c 100644
--- a/README.md
+++ b/README.md
@@ -108,7 +108,7 @@ jobs:
 | `working-directory`      | Directory passed to `codex exec --cd`. Defaults to the repository root.                                                                        | `""`        |
 | `sandbox`                | Legacy sandbox mode. Prefer `permission-profile: ":workspace"` for new workflows. Mutually exclusive with `permission-profile`.               | `""`        |
 | `permission-profile`     | Built-in or configured [Codex permission profile](https://developers.openai.com/codex/permissions) selected through `default_permissions`.      | `""`        |
-| `codex-version`          | Version of `@openai/codex` to install.                                                                                                         | `""`        |
+| `codex-version`          | Version, tag, or range of `@openai/codex` to install. If unset, resolves the latest published version at run time; pin it for reproducible builds. | `""`        |
 | `codex-args`             | Extra arguments forwarded to `codex exec`. Accepts JSON arrays (`["--flag", "value"]`) or shell-style strings.                                 | `""`        |
 | `output-schema`          | Inline schema contents written to a temp file and passed to `codex exec --output-schema`. Mutually exclusive with `output-schema-file`.        | `""`        |
 | `output-schema-file`     | Schema file forwarded to `codex exec --output-schema`. Leave empty to skip passing the option.                                                 | `""`        |
@@ -185,6 +185,7 @@ See [Protecting your `OPENAI_API_KEY`](./docs/security.md#protecting-your-openai
 | Name            | Description                             |
 | --------------- | --------------------------------------- |
 | `final-message` | Final message returned by `codex exec`. |
+| `codex-version` | Exact `@openai/codex` version installed for the run. |
 
 As we saw in the example above, we took the `final-message` output of the `run_codex` step and made it an output of the `codex` job in the workflow:
 
@@ -194,6 +195,7 @@ jobs:
     # ...
     outputs:
       final_message: ${{ steps.run_codex.outputs.final-message }}
+      codex_version: ${{ steps.run_codex.outputs.codex-version }}
 ```
 
 ## Additional tips
diff --git a/action.yml b/action.yml
index ff7088b..c12ef06 100644
--- a/action.yml
+++ b/action.yml
@@ -41,7 +41,7 @@ inputs:
     required: false
     default: ""
   codex-version:
-    description: "Version of `@openai/codex` to install."
+    description: "Version, tag, or range of `@openai/codex` to install. Leave empty to resolve the latest published version at run time."
     required: false
     default: ""
   codex-args:
@@ -124,6 +124,9 @@ outputs:
   final-message:
     description: "Raw output emitted by `codex exec`."
     value: ${{ steps.run_codex.outputs['final-message'] }}
+  codex-version:
+    description: "Exact installed `@openai/codex` version resolved for this run."
+    value: ${{ steps.resolve_codex_version.outputs.codex-version }}
 runs:
   using: "composite"
   steps:
@@ -161,10 +164,24 @@ runs:
           --allow-users "$ALLOW_USERS"
 
     - name: Install Codex CLI
+      id: resolve_codex_version
       shell: bash
       env:
         CODEX_VERSION: ${{ inputs['codex-version'] }}
-      run: npm install -g "@openai/codex@${CODEX_VERSION}"
+      run: |
+        npm install -g "@openai/codex@${CODEX_VERSION}"
+
+        codex_root="$(npm root -g)"
+        resolved_codex_version="$(node -p 'require(process.argv[1]).version' "$codex_root/@openai/codex/package.json")"
+
+        echo "codex-version=$resolved_codex_version" >> "$GITHUB_OUTPUT"
+        echo "Installed Codex CLI version: $resolved_codex_version"
+        {
+          echo "### Codex CLI"
+          echo
+          echo "- Resolved version: \
+\`$resolved_codex_version\`"
+        } >> "$GITHUB_STEP_SUMMARY"
 
     - name: Install Codex Responses API proxy
       shell: bash
diff --git a/test/actionHardening.test.mjs b/test/actionHardening.test.mjs
index d8aed0f..e0d47bf 100644
--- a/test/actionHardening.test.mjs
+++ b/test/actionHardening.test.mjs
@@ -37,6 +37,27 @@ test("Responses proxy replaces inherited Node options without exposing its API k
   assert.doesNotMatch(step, /printenv PROXY_API_KEY\s*\|/);
 });
 
+test("action exposes the resolved codex version as an output", () => {
+  assert.match(
+    action,
+    /outputs:\n  final-message:[\s\S]*\n  codex-version:\n    description: "Exact installed `@openai\/codex` version resolved for this run\."\n    value: \$\{\{ steps\.resolve_codex_version\.outputs\.codex-version \}\}/
+  );
+});
+
+test("action reports the installed codex version without changing proxy resolution", () => {
+  const installCodexStep = actionStep("Install Codex CLI");
+  const installProxyStep = actionStep("Install Codex Responses API proxy");
+
+  assert.match(installCodexStep, /id: resolve_codex_version/);
+  assert.match(installCodexStep, /resolved_codex_version=.*@openai\/codex\/package\.json/);
+  assert.match(installCodexStep, /echo "codex-version=\$resolved_codex_version" >> "\$GITHUB_OUTPUT"/);
+  assert.match(installCodexStep, /GITHUB_STEP_SUMMARY/);
+  assert.match(
+    installProxyStep,
+    /CODEX_VERSION: \$\{\{ inputs\['codex-version'\] \}\}/
+  );
+});
+
 test(
   "Responses proxy environment removes unsafe Node options and its API key",
   { skip: process.platform === "win32" },