diff --git a/anton/cloud_turn/contract.py b/anton/cloud_turn/contract.py
index da63d219..16d2f2e4 100644
--- a/anton/cloud_turn/contract.py
+++ b/anton/cloud_turn/contract.py
@@ -235,6 +235,10 @@ class TurnRequestV1:
     #: {engine: {"usage_notes": str}}. Rendered only for engines the turn's
     #: vault connects. Absent when no connected engine has notes.
     connectors: dict | None = None
+    #: Optional reasoning effort the user picked for this turn. Applied to the
+    #: planning model only; the name is passed to the provider uninterpreted.
+    #: Absent, null, blank, or non-string keeps the configured default.
+    reasoning_effort: str | None = None
 
     @staticmethod
     def from_json(raw: str) -> "TurnRequestV1":
@@ -242,6 +246,9 @@ def from_json(raw: str) -> "TurnRequestV1":
         protocol_version = d["protocol_version"]
         if not _is_version(protocol_version, TURN_PROTOCOL_VERSION):
             raise ValueError("unsupported cloud turn protocol version")
+        reasoning_effort = d.get("reasoning_effort")
+        if not isinstance(reasoning_effort, str):
+            reasoning_effort = ""
         return TurnRequestV1(
             protocol_version=protocol_version,
             conversation_id=str(d["conversation_id"]),
@@ -270,4 +277,5 @@ def from_json(raw: str) -> "TurnRequestV1":
             connectors=(
                 d.get("connectors") if isinstance(d.get("connectors"), dict) else None
             ),
+            reasoning_effort=reasoning_effort.strip() or None,
         )
diff --git a/anton/cloud_turn/session.py b/anton/cloud_turn/session.py
index 6e22e588..bf7e0339 100644
--- a/anton/cloud_turn/session.py
+++ b/anton/cloud_turn/session.py
@@ -758,6 +758,10 @@ def build_cloud_chat_session(
     settings.resolve_workspace(str(base))
     if request.model:
         settings.planning_model = request.model
+    # Planning only: the router shares the coding provider, so changing coding
+    # effort would also change history summarization.
+    if request.reasoning_effort:
+        settings.planning_reasoning_effort = request.reasoning_effort
     # Mounted (_SKILLS_ROOT_ENV set): the organization's own live skills tree,
     # owned by cowork-server, read directly. Unmounted (desktop, CI): the
     # request's skills are staged outside the workspace instead, since that PVC
diff --git a/tests/test_cloud_turn_contract.py b/tests/test_cloud_turn_contract.py
index f0f90ebd..c6b1f38f 100644
--- a/tests/test_cloud_turn_contract.py
+++ b/tests/test_cloud_turn_contract.py
@@ -89,3 +89,25 @@ def test_a_missing_or_non_object_connectors_block_parses_to_none(value):
     if value is not None:
         body["connectors"] = value
     assert TurnRequestV1.from_json(json.dumps(body)).connectors is None
+
+
+def _with_effort(**extra):
+    """The parsed request for a minimal body carrying ``extra``."""
+    body = {"protocol_version": 1, "conversation_id": "c", "input": "hi"}
+    body.update(extra)
+    return TurnRequestV1.from_json(json.dumps(body))
+
+
+@pytest.mark.parametrize("effort", ["low", "none", "high", "some-future-level"])
+def test_reasoning_effort_is_passed_through_uninterpreted(effort):
+    assert _with_effort(reasoning_effort=effort).reasoning_effort == effort
+
+
+@pytest.mark.parametrize("extra", [{}, {"reasoning_effort": None}, {"reasoning_effort": ""}, {"reasoning_effort": "  "}])
+def test_absent_null_or_blank_reasoning_effort_is_unset(extra):
+    assert _with_effort(**extra).reasoning_effort is None
+
+
+@pytest.mark.parametrize("effort", [1, True, ["high"], {"level": "high"}, 0.5])
+def test_a_non_string_reasoning_effort_falls_back_to_the_default(effort):
+    assert _with_effort(reasoning_effort=effort).reasoning_effort is None
diff --git a/tests/test_cloud_turn_session.py b/tests/test_cloud_turn_session.py
index aa4c471f..5ebd4552 100644
--- a/tests/test_cloud_turn_session.py
+++ b/tests/test_cloud_turn_session.py
@@ -20,6 +20,8 @@
 # `_pin_today` later replaces on the module.
 from datetime import datetime as _stdlib_datetime
 
+import httpx2 as httpx
+import openai
 import pytest
 
 import anton.core.llm.client as llm_client_mod
@@ -1280,6 +1282,124 @@ def fake_minds_request(url, api_key, *, method="GET", payload=None, verify=True,
     assert "DS_GMAIL_PRIMARY__ACCESS_TOKEN" not in os.environ
 
 
+_MINDS_LLM = {"provider": "minds-cloud", "api_key": "mdb_k", "base_url": "https://api.mindshub.ai"}
+
+
+def _build_real_client(tmp_path, monkeypatch, **req_overrides):
+    """The real LLMClient a cloud turn builds for this request, with ChatSession faked."""
+    captured: dict = {}
+    real_from_settings = llm_client_mod.LLMClient.from_settings.__func__
+
+    def capture(cls, settings):
+        captured["client"] = real_from_settings(cls, settings)
+        return captured["client"]
+
+    monkeypatch.setattr(session_mod, "ChatSession", lambda config: _FakeSession())
+    monkeypatch.setattr(llm_client_mod.LLMClient, "from_settings", classmethod(capture))
+    monkeypatch.setenv(_WORKSPACE_PATH_ENV, str(tmp_path))
+    body = dict(protocol_version=1, conversation_id="conv_1", input="hello", llm=_MINDS_LLM)
+    body.update(req_overrides)
+    build_cloud_chat_session(TurnRequestV1(**body))
+    return captured["client"]
+
+
+def _chat_stream(text: str) -> bytes:
+    """``text`` as a streamed chat.completions answer, the format the minds passthrough reads."""
+    chunk = {"id": "chatcmpl-1", "object": "chat.completion.chunk", "created": 0, "model": "m"}
+    chunks = [
+        {**chunk, "choices": [{"index": 0, "delta": {"role": "assistant", "content": text},
+                               "finish_reason": None}]},
+        {**chunk, "choices": [{"index": 0, "delta": {}, "finish_reason": "stop"}]},
+    ]
+    return ("".join(f"data: {json.dumps(c)}\n\n" for c in chunks) + "data: [DONE]\n\n").encode()
+
+
+def _record_requests(monkeypatch) -> list[tuple[str, dict]]:
+    """Point every OpenAI SDK client built from now on at a transport that
+    records each request as (path, body) and answers it with a short completion."""
+    requests: list[tuple[str, dict]] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        sent = json.loads(request.content)
+        requests.append((request.url.path, sent))
+        if sent.get("stream"):
+            return httpx.Response(
+                200, headers={"content-type": "text/event-stream"},
+                content=_chat_stream("answered"),
+            )
+        return httpx.Response(200, json={
+            "id": "chatcmpl-1", "object": "chat.completion", "created": 0, "model": "m",
+            "choices": [{"index": 0, "finish_reason": "stop",
+                         "message": {"role": "assistant", "content": "answered"}}],
+            "usage": {"prompt_tokens": 1, "completion_tokens": 1, "total_tokens": 2},
+        })
+
+    real_async_openai = openai.AsyncOpenAI
+
+    def mock_async_openai(**kwargs):
+        kwargs["http_client"] = httpx.AsyncClient(transport=httpx.MockTransport(handler))
+        return real_async_openai(**{**kwargs, "max_retries": 0})
+
+    monkeypatch.setattr(openai, "AsyncOpenAI", mock_async_openai)
+    return requests
+
+
+async def _efforts_on_the_wire(client, requests) -> dict[str, str | None]:
+    """One call per role; the ``reasoning_effort`` each chat.completions request carried."""
+    messages = [{"role": "user", "content": "hi"}]
+    async for _ in client.plan_stream(system="s", messages=messages):
+        pass
+    async for _ in client.code_stream(system="s", messages=messages):
+        pass
+    await client.summarize(system="s", messages=messages)
+    assert [path for path, _ in requests] == ["/v1/chat/completions"] * 3
+    efforts = (sent.get("reasoning_effort") for _, sent in requests)
+    return dict(zip(("planning", "coding", "router"), efforts))
+
+
+@pytest.mark.parametrize("coding_model", [None, "claude-opus-4-6"])
+@pytest.mark.parametrize("router", [False, True])
+async def test_selected_effort_reaches_only_the_planning_request(tmp_path, monkeypatch, coding_model, router):
+    """The router shares the coding provider unless one is configured, so
+    coding effort must stay put or history summarization would change too."""
+    if router:
+        monkeypatch.setenv("ANTON_ROUTER_PROVIDER", "openai-compatible")
+    monkeypatch.setenv("ANTON_CODING_REASONING_EFFORT", "medium")
+    requests = _record_requests(monkeypatch)
+    llm = dict(_MINDS_LLM, coding_model=coding_model) if coding_model else _MINDS_LLM
+    client = _build_real_client(
+        tmp_path, monkeypatch, model="claude-opus-4-6", llm=llm, reasoning_effort="low",
+    )
+    try:
+        sent = await _efforts_on_the_wire(client, requests)
+    finally:
+        await client.aclose()
+    assert sent == {"planning": "low", "coding": "medium", "router": None if router else "medium"}
+
+
+async def test_no_selected_effort_keeps_the_configured_planning_effort(tmp_path, monkeypatch):
+    """With nothing selected, planning carries the configured effort and the other roles none."""
+    monkeypatch.setenv("ANTON_PLANNING_REASONING_EFFORT", "high")
+    requests = _record_requests(monkeypatch)
+    client = _build_real_client(tmp_path, monkeypatch, reasoning_effort=None)
+    try:
+        sent = await _efforts_on_the_wire(client, requests)
+    finally:
+        await client.aclose()
+    assert sent == {"planning": "high", "coding": None, "router": None}
+
+
+async def test_no_selected_or_configured_effort_sends_none(tmp_path, monkeypatch):
+    """With nothing selected or configured, no request carries an effort."""
+    requests = _record_requests(monkeypatch)
+    client = _build_real_client(tmp_path, monkeypatch)
+    try:
+        sent = await _efforts_on_the_wire(client, requests)
+    finally:
+        await client.aclose()
+    assert sent == {"planning": None, "coding": None, "router": None}
+
+
 # ── ENG-1638: the pod injects a configured-LLM block ─────────────────────────
 
 def test_pod_injects_a_configured_llm_block_for_the_runtime_identity(tmp_path, monkeypatch):