diff --git a/gateway/platforms/api_server.py b/gateway/platforms/api_server.py
index f02af4bacc..8183521d86 100644
--- a/gateway/platforms/api_server.py
+++ b/gateway/platforms/api_server.py
@@ -116,6 +116,7 @@ except ImportError:
     web = None  # type: ignore[assignment]
 
 from gateway.config import Platform, PlatformConfig
+from gateway.display_config import resolve_display_setting
 from gateway.platforms import api_server_room_dispatch as _room_dispatch
 from gateway.platforms import api_server_room_grants as _room_grants
 from gateway.platforms import api_server_runs as _api_runs
@@ -2181,6 +2182,10 @@ class APIServerAdapter(OpenAICompatRoutesMixin, BasePlatformAdapter):
             gateway_session_key=gateway_session_key, session_id=session_id)
         user_config = _load_gateway_config()
         enabled_toolsets = sorted(_get_platform_tools(user_config, "api_server"))
+        # Same gate the messaging gateway and TUI apply: ``display.interim_assistant_messages``
+        # off means no callback is installed, so mid-turn commentary never leaves the agent.
+        if not resolve_display_setting(user_config, "api_server", "interim_assistant_messages", True):
+            interim_assistant_callback = None
         max_iterations = _current_max_iterations()
         if room_dispatch is not None:
             from gateway.hosted_room_execution_policy import RoomExecutionPolicy
diff --git a/gateway/platforms/api_server_runs.py b/gateway/platforms/api_server_runs.py
index ea7efb7f1a..ae290cf44f 100644
--- a/gateway/platforms/api_server_runs.py
+++ b/gateway/platforms/api_server_runs.py
@@ -728,6 +728,16 @@ async def _execute_run(self, run: _RunLaunch, *, _api_server) -> None:
         with suppress(Exception):
             loop.call_soon_threadsafe(run.put_event, _run_event(run_id, "message.delta", delta=delta))
 
+    def _interim_cb(text: str, *, already_streamed: bool = False) -> None:
+        # Mid-turn assistant commentary (Codex ``phase="commentary"``, text beside tool calls),
+        # same ``message.interim`` contract as the TUI gateway; reasoning never reaches this
+        # callback and the final answer still arrives via ``run.completed`` (#67580).
+        if not isinstance(text, str) or not text.strip() or run_id not in self._run_streams:
+            return
+        with suppress(Exception):
+            loop.call_soon_threadsafe(run.put_event, _run_event(
+                run_id, "message.interim", text=text, already_streamed=bool(already_streamed)))
+
     def _finish(status: str, extra: Optional[dict] = None, **fields: Any) -> None:
         """Terminal status, then best-effort ``run.<status>`` event; key order is wire shape."""
         extra = extra or {}
@@ -752,7 +762,7 @@ async def _execute_run(self, run: _RunLaunch, *, _api_server) -> None:
         with self._profile_scope(run.request_profile):
             agent = self._create_agent(
                 stream_delta_callback=_text_cb, tool_progress_callback=self._make_run_event_callback(run_id, loop),
-                **run.agent_kwargs)
+                interim_assistant_callback=_interim_cb, **run.agent_kwargs)
         self._active_run_agents[run_id] = agent
         approval_notify = _make_approval_notify(self, run, _api_server=_api_server)
         result, usage = await loop.run_in_executor(
diff --git a/tests/gateway/test_api_server_runs.py b/tests/gateway/test_api_server_runs.py
index 279cab2d5b..a85b235e0f 100644
--- a/tests/gateway/test_api_server_runs.py
+++ b/tests/gateway/test_api_server_runs.py
@@ -337,6 +337,39 @@ class TestStartRun:
         assert adapter._run_statuses == {}
         mock_create.assert_not_called()
 
+    @pytest.mark.asyncio
+    async def test_events_stream_forwards_interim_commentary(self, adapter):
+        """Mid-turn assistant commentary (Codex ``phase="commentary"``) reaches /v1/runs clients
+        as ``message.interim`` {text, already_streamed}; the final answer is unchanged (#67580)."""
+        import json
+
+        app = _create_runs_app(adapter)
+
+        def create_agent(**kwargs):
+            interim = kwargs["interim_assistant_callback"]
+            agent = MagicMock()
+
+            def run_conversation(**_kw):
+                interim("Checking the docs first.", already_streamed=False)
+                interim("Applying the fix.", already_streamed=True)
+                return {"final_response": "Done."}
+
+            agent.run_conversation.side_effect = run_conversation
+            agent.session_prompt_tokens = agent.session_completion_tokens = agent.session_total_tokens = 0
+            return agent
+
+        async with TestClient(TestServer(app)) as cli:
+            with patch.object(adapter, "_create_agent", side_effect=create_agent):
+                resp = await cli.post("/v1/runs", json={"input": "hello"})
+                run_id = (await resp.json())["run_id"]
+                body = await (await cli.get(f"/v1/runs/{run_id}/events")).text()
+
+        events = [json.loads(line[6:]) for line in body.splitlines() if line.startswith("data: ")]
+        interim = [(e["text"], e["already_streamed"]) for e in events if e["event"] == "message.interim"]
+        assert interim == [("Checking the docs first.", False), ("Applying the fix.", True)]
+        completed = next(e for e in events if e["event"] == "run.completed")
+        assert completed["output"] == "Done."
+
     @pytest.mark.asyncio
     async def test_start_passes_request_model_provider_options_to_create_agent(self, adapter):
         app = _create_runs_app(adapter)
diff --git a/tests/gateway/test_session_api.py b/tests/gateway/test_session_api.py
index 1973d947e0..e97b128de8 100644
--- a/tests/gateway/test_session_api.py
+++ b/tests/gateway/test_session_api.py
@@ -1155,3 +1155,69 @@ async def test_session_stream_records_reply_text_for_post_disconnect_recovery(
     response = await adapter._handle_get_run(get_request)
     assert response.status == 200
     assert "the answer worth keeping" in response.text
+
+
+@pytest.mark.asyncio
+async def test_interim_commentary_reaches_session_sse_and_responses_stream(adapter, session_db, monkeypatch):
+    """Codex commentary / mid-turn assistant text is a typed ``assistant.commentary`` event on the
+    session SSE endpoint and a ``phase: commentary`` message item on /v1/responses, never part of
+    the final answer; ``display.interim_assistant_messages: false`` installs no callback (#67580)."""
+    import json as _json
+
+    session_id = session_db.create_session("commentary-session", "api_server")
+
+    def fake_create_agent(**kwargs):
+        interim = kwargs["interim_assistant_callback"]
+
+        class FakeAgent:
+            provider, model = "openai-codex", "gpt-5"
+            session_prompt_tokens = session_completion_tokens = session_total_tokens = 0
+
+            def run_conversation(self, **_kw):
+                interim("Checking the docs first.", already_streamed=False)
+                return {"final_response": "Done.", "messages": [], "api_calls": 1}
+
+        return FakeAgent()
+
+    app = _create_session_app(adapter)
+    app.router.add_post("/v1/responses", adapter._handle_responses)
+    with patch.object(adapter, "_create_agent", side_effect=fake_create_agent):
+        async with TestClient(TestServer(app)) as cli:
+            sse = await (await cli.post(f"/api/sessions/{session_id}/chat/stream", json={"message": "go"})).text()
+            responses = await (await cli.post(
+                "/v1/responses", json={"model": "hermes-agent", "input": "go", "stream": True})).text()
+
+    def _events(body):
+        out = []
+        for block in body.split("\n\n"):
+            lines = block.splitlines()
+            name = next((ln[7:] for ln in lines if ln.startswith("event: ")), None)
+            data = next((ln[6:] for ln in lines if ln.startswith("data: ")), None)
+            if data:
+                out.append((name, _json.loads(data)))
+        return out
+
+    sse_events = _events(sse)
+    commentary = [d for n, d in sse_events if n == "assistant.commentary"]
+    assert [(d["text"], d["already_streamed"]) for d in commentary] == [("Checking the docs first.", False)]
+    assert next(d for n, d in sse_events if n == "assistant.completed")["content"] == "Done."
+
+    done_items = [d["item"] for n, d in _events(responses) if n == "response.output_item.done"]
+    assert [(i.get("phase"), i["content"][0]["text"]) for i in done_items if i["type"] == "message"] == [
+        ("commentary", "Checking the docs first."), (None, "Done.")]
+
+    # Display gate: the callback is dropped before it reaches AIAgent, like the gateway/TUI.
+    _patch_api_server_runtime(monkeypatch)
+    monkeypatch.setattr(
+        "gateway.run._load_gateway_config", lambda: {"display": {"interim_assistant_messages": False}})
+    captured = {}
+
+    class CapturingAgent:
+        provider, model = "openrouter", "global/model"
+
+        def __init__(self, **kwargs):
+            captured.update(kwargs)
+
+    monkeypatch.setattr("run_agent.AIAgent", CapturingAgent)
+    adapter._create_agent(session_id="gated", interim_assistant_callback=lambda *_a, **_k: None)
+    assert captured["interim_assistant_callback"] is None
diff --git a/website/docs/user-guide/features/api-server.md b/website/docs/user-guide/features/api-server.md
index 9e8fc51379..752e6e732b 100644
--- a/website/docs/user-guide/features/api-server.md
+++ b/website/docs/user-guide/features/api-server.md
@@ -146,6 +146,8 @@ OpenAI Responses API format. Supports server-side conversation state via `previo
 
 Tool calls in the `output` array were already executed server-side by the Hermes agent — they are replayed with `"status": "completed"` for structured tool UI, never as pending calls for the client to execute.
 
+With `"stream": true`, mid-turn assistant commentary (the `openai-codex` backend's `phase="commentary"` progress preambles, or text a model writes alongside its tool calls) arrives as its own completed `message` output item carrying `"phase": "commentary"` (`response.output_item.added` + `response.output_item.done`, also listed in `response.completed`). It is never merged into the final answer item, so clients can render it as live progress and skip it when assembling the reply. Private reasoning never reaches this item. `display.interim_assistant_messages: false` (or the `display.platforms.api_server` override) suppresses it on every API-server surface.
+
 **Inline image input:** `input[].content` can contain `input_text` and `input_image` parts. Both remote URLs and `data:image/...` URLs are supported:
 
 ```json
@@ -475,6 +477,13 @@ Statuses are retained briefly after terminal states (`completed`, `failed`, `can
 
 Server-Sent Events stream of the run's tool-call progress, token deltas, and lifecycle events. Designed for dashboards and thick clients that want to attach/detach without losing state.
 
+Mid-turn assistant commentary — the `openai-codex` backend's `phase="commentary"` progress
+preambles, or text a model writes alongside its tool calls — arrives as `message.interim`
+(`text`, `already_streamed`), the same contract the TUI gateway uses. `already_streamed: true`
+means the text also went out as `message.delta`, so clients that render deltas can skip it.
+The final answer still arrives only in `run.completed`; private reasoning never becomes
+`message.interim`. Gate: `display.interim_assistant_messages` (default `true`).
+
 Tool lifecycle events carry `tool.started` (`tool`, `preview` of the arguments) and
 `tool.completed` (`tool`, `duration` in seconds, `error`, and a `preview` of the result). The
 `error` flag reflects the tool's own outcome — a non-zero terminal `exit_code`, a structured
@@ -590,7 +599,7 @@ External UIs can manage Hermes sessions over REST without standing up the dashbo
 | `GET` | `/api/sessions/{id}/messages` | Message history for a session |
 | `POST` | `/api/sessions/{id}/fork` | Branch the session via `SessionDB` lineage (matches CLI `/branch` semantics) |
 | `POST` | `/api/sessions/{id}/chat` | Run one synchronous agent turn |
-| `POST` | `/api/sessions/{id}/chat/stream` | SSE wrapper over a single turn — emits `assistant.delta`, `tool.started`, `tool.completed`, then a terminal `run.completed` / `run.failed` / `run.cancelled` event that matches how the turn ended (see [Terminal run status](../../developer-guide/programmatic-integration.md#terminal-run-status)) |
+| `POST` | `/api/sessions/{id}/chat/stream` | SSE wrapper over a single turn — emits `assistant.delta`, `assistant.commentary` (mid-turn commentary: `message_id`, `text`, `already_streamed`; never folded into `assistant.completed`), `tool.started`, `tool.completed`, then a terminal `run.completed` / `run.failed` / `run.cancelled` event that matches how the turn ended (see [Terminal run status](../../developer-guide/programmatic-integration.md#terminal-run-status)) |
 
 `/v1/capabilities` advertises the full surface via `session_*` feature flags and `endpoints.session_*` entries so external UIs can detect support and fall back safely. Inline images are supported in `chat` and `chat/stream` payloads (multimodal-aware path).