diff --git a/frontend/search-batch-plan.js b/frontend/search-batch-plan.js
index 839d15d..360449c 100644
--- a/frontend/search-batch-plan.js
+++ b/frontend/search-batch-plan.js
@@ -169,21 +169,14 @@
       queue:async (confirmed, context) => {
         const issuePath = 'api/v1/repos/' + confirmed.repository.split('/').map(encodeURIComponent).join('/') +
           '/issues/' + encodeURIComponent(confirmed.number);
-        const milestone = await fetchJson(issuePath + '/milestone', {
+        const releasePlan = await fetchJson(issuePath + '/release-plan', {
           method:'PATCH', headers:{Accept:'application/json','Content-Type':'application/json'},
-          body:JSON.stringify({milestone_id:context.milestone_id}),
+          body:JSON.stringify({milestone_id:context.milestone_id, due_date:context.due_date || null}),
         });
-        if (milestone?.number !== confirmed.number || milestone?.milestone?.id !== context.milestone_id) {
-          throw new Error('Issue milestone was not confirmed.');
-        }
-        if (context.due_date) {
-          const deadline = await fetchJson(issuePath + '/due-date', {
-            method:'PATCH', headers:{Accept:'application/json','Content-Type':'application/json'},
-            body:JSON.stringify({due_date:context.due_date}),
-          });
-          if (deadline?.number !== confirmed.number || deadline?.due_date !== context.due_date) {
-            throw new Error('Issue due date was not confirmed.');
-          }
+        if (releasePlan?.number !== confirmed.number ||
+            releasePlan?.milestone?.id !== context.milestone_id ||
+            (context.due_date && releasePlan?.due_date !== context.due_date)) {
+          throw new Error('Issue release plan was not confirmed.');
         }
         return 'queued';
       },
diff --git a/src/gitea_proxy.py b/src/gitea_proxy.py
index b79d807..6ac0d4e 100644
--- a/src/gitea_proxy.py
+++ b/src/gitea_proxy.py
@@ -1969,6 +1969,58 @@ async def update_assigned_issue_milestone(
     }
 
 
+async def update_assigned_issue_release_plan(
+    repository: str, number: int, milestone_id: int, due_date: str | None
+) -> dict:
+    path = f"repos/{repository}/issues/{number}"
+    login, issue = await _current_login_and_target(path)
+    if (
+        issue.get("state") != "open"
+        or isinstance(issue.get("pull_request"), dict)
+        or not _login_in_users(login, issue.get("assignees"))
+    ):
+        raise IssueNotAvailableError("assigned issue not found")
+
+    selected = next(
+        (item for item in await repo_milestones(repository) if item["id"] == milestone_id),
+        None,
+    )
+    if selected is None:
+        raise ValueError("Unknown open repository milestone")
+
+    payload: dict = {"milestone": milestone_id}
+    if due_date is not None:
+        payload["due_date"] = due_date
+    response = await _get_client().patch(
+        f"/api/v1/{path}", headers=_auth(), json=payload
+    )
+    response.raise_for_status()
+    confirmed = response.json()
+    milestone_value = confirmed.get("milestone") if isinstance(confirmed, dict) else None
+    normalized = (
+        {"id": milestone_value["id"], "title": milestone_value["title"]}
+        if isinstance(milestone_value, dict)
+        and isinstance(milestone_value.get("id"), int)
+        and isinstance(milestone_value.get("title"), str)
+        else None
+    )
+    expected_due_date = due_date if due_date is not None else issue.get("due_date")
+    if (
+        not isinstance(confirmed, dict)
+        or confirmed.get("number") != number
+        or normalized != selected
+        or confirmed.get("due_date") != expected_due_date
+    ):
+        raise ValueError("Gitea did not confirm the issue release plan")
+    return {
+        "repository": repository,
+        "number": number,
+        "state": confirmed.get("state", "open"),
+        "milestone": normalized,
+        "due_date": confirmed.get("due_date"),
+    }
+
+
 async def issue_conversation_page(
     repository: str,
     number: int,
diff --git a/src/main.py b/src/main.py
index 4c218fa..1a2781a 100644
--- a/src/main.py
+++ b/src/main.py
@@ -763,6 +763,15 @@ class IssueMilestoneUpdate(BaseModel):
     milestone_id: PositiveInt | None = None
 
 
+class IssueReleasePlanUpdate(BaseModel):
+    milestone_id: PositiveInt
+    due_date: str | None = Field(
+        default=None,
+        pattern=r"^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z$",
+        max_length=20,
+    )
+
+
 class IssueHandoff(BaseModel):
     recipient: str = Field(
         min_length=1, max_length=255, pattern=r"^[A-Za-z0-9_.-]+$"
@@ -4374,6 +4383,40 @@ async def update_assigned_issue_milestone(
     return JSONResponse(result)
 
 
+@app.patch("/api/v1/repos/{owner}/{repo}/issues/{number}/release-plan")
+async def update_assigned_issue_release_plan(
+    update: IssueReleasePlanUpdate,
+    owner: str,
+    repo: str,
+    number: int = PathParam(gt=0),
+):
+    repository = f"{owner}/{repo}"
+    try:
+        result = await asyncio.wait_for(
+            gitea_proxy.update_assigned_issue_release_plan(
+                repository, number, update.milestone_id, update.due_date
+            ),
+            timeout=ISSUE_ACTION_TIMEOUT_SECONDS,
+        )
+    except gitea_proxy.IssueNotAvailableError:
+        raise HTTPException(status_code=404, detail="Assigned issue not found")
+    except ValueError as exc:
+        if str(exc) == "Unknown open repository milestone":
+            raise HTTPException(status_code=422, detail=str(exc))
+        return JSONResponse(
+            {"error": "The release plan could not be confirmed. Your selection is safe; please retry."},
+            status_code=503,
+            headers={"Retry-After": "1"},
+        )
+    except Exception:
+        return JSONResponse(
+            {"error": "The release plan could not be updated. Your selection is safe; please retry."},
+            status_code=503,
+            headers={"Retry-After": "1"},
+        )
+    return JSONResponse(result)
+
+
 @app.get("/api/v1/repos/{owner}/{repo}/milestones")
 async def repository_milestones(owner: str, repo: str):
     repository = f"{owner}/{repo}"
diff --git a/tests/test_issue_api.py b/tests/test_issue_api.py
index 5472a5d..b411ba3 100644
--- a/tests/test_issue_api.py
+++ b/tests/test_issue_api.py
@@ -215,6 +215,81 @@ async def test_gitea_milestone_update_revalidates_assignment_and_open_repository
     }
 
 
+@pytest.mark.anyio
+@pytest.mark.parametrize("due_date", ["2026-08-31T23:59:59Z", None])
+async def test_release_plan_applies_milestone_and_optional_deadline_in_one_patch(due_date):
+    requests = []
+    existing_due_date = "2026-08-20T23:59:59Z"
+
+    async def handler(request):
+        requests.append(request)
+        if request.url.path == "/api/v1/user":
+            return httpx.Response(200, json={"login": "timmy"})
+        if request.method == "GET" and request.url.path.endswith("/issues/17"):
+            return httpx.Response(200, json={
+                "number": 17, "state": "open", "pull_request": None,
+                "assignees": [{"login": "timmy"}], "due_date": existing_due_date,
+            })
+        if request.method == "GET" and request.url.path.endswith("/milestones"):
+            return httpx.Response(200, json=[
+                {"id": 9, "title": "August RC", "state": "open"},
+            ])
+        return httpx.Response(200, json={
+            "number": 17, "state": "open",
+            "milestone": {"id": 9, "title": "August RC"},
+            "due_date": due_date or existing_due_date,
+        })
+
+    gitea_proxy.start_client(transport=httpx.MockTransport(handler))
+    try:
+        result = await gitea_proxy.update_assigned_issue_release_plan(
+            "stackchain/api", 17, 9, due_date
+        )
+    finally:
+        await gitea_proxy.stop_client()
+
+    patch_requests = [request for request in requests if request.method == "PATCH"]
+    assert len(patch_requests) == 1
+    expected_payload = {"milestone": 9}
+    if due_date:
+        expected_payload["due_date"] = due_date
+    assert json.loads(patch_requests[0].content) == expected_payload
+    assert result == {
+        "repository": "stackchain/api", "number": 17, "state": "open",
+        "milestone": {"id": 9, "title": "August RC"},
+        "due_date": due_date or existing_due_date,
+    }
+
+
+@pytest.mark.anyio
+async def test_release_plan_endpoint_is_bounded_and_returns_confirmed_plan(monkeypatch):
+    calls = []
+
+    async def update(repository, number, milestone_id, due_date):
+        calls.append((repository, number, milestone_id, due_date))
+        return {
+            "repository": repository, "number": number, "state": "open",
+            "milestone": {"id": milestone_id, "title": "August RC"},
+            "due_date": due_date,
+        }
+
+    monkeypatch.setattr(
+        main.gitea_proxy, "update_assigned_issue_release_plan", update, raising=False
+    )
+    transport = httpx.ASGITransport(app=main.app)
+    async with httpx.AsyncClient(transport=transport, base_url="http://test") as client:
+        response = await client.patch(
+            "/api/v1/repos/stackchain/api/issues/17/release-plan",
+            json={"milestone_id": 9, "due_date": "2026-08-31T23:59:59Z"},
+        )
+
+    assert response.status_code == 200
+    assert response.headers["cache-control"] == "no-store"
+    assert response.json()["milestone"] == {"id": 9, "title": "August RC"}
+    assert response.json()["due_date"] == "2026-08-31T23:59:59Z"
+    assert calls == [("stackchain/api", 17, 9, "2026-08-31T23:59:59Z")]
+
+
 @pytest.mark.anyio
 async def test_milestone_routes_are_repository_bounded_and_no_store(monkeypatch):
     calls = []
diff --git a/tests/test_search_batch_plan.py b/tests/test_search_batch_plan.py
index 848fd8e..1e0664b 100644
--- a/tests/test_search_batch_plan.py
+++ b/tests/test_search_batch_plan.py
@@ -293,8 +293,9 @@ const fetchJson=(url,options={{}})=>{{
   calls.push({{url,method:options.method || 'GET',body:options.body ? JSON.parse(options.body) : null}});
   if (url.endsWith('/milestones')) return Promise.resolve([{{id:9,title:'August RC'}},{{id:7,title:'Old',state:'closed'}}]);
   const number=Number(url.split('/issues/')[1].split('/')[0]);
-  if (url.endsWith('/milestone')) return Promise.resolve({{number,milestone:{{id:9,title:'August RC'}}}});
-  if (url.endsWith('/due-date')) return Promise.resolve({{number,due_date:'2026-08-31T23:59:59Z'}});
+  if (url.endsWith('/release-plan')) return Promise.resolve({{
+    number,milestone:{{id:9,title:'August RC'}},due_date:'2026-08-31T23:59:59Z'
+  }});
   return Promise.resolve();
 }};
 const processorOptions=[];
@@ -346,16 +347,11 @@ listeners['plan-selected-search-results:click']().then(async()=>{{
             "due_date": "2026-08-31T23:59:59Z",
         },
     }
-    assert result["calls"][2:] == [
-        {
-            "url": "api/v1/repos/stackchain/dashboard/issues/815/milestone",
-            "method": "PATCH", "body": {"milestone_id": 9},
-        },
-        {
-            "url": "api/v1/repos/stackchain/dashboard/issues/815/due-date",
-            "method": "PATCH", "body": {"due_date": "2026-08-31T23:59:59Z"},
-        },
-    ]
+    assert result["calls"][2:] == [{
+        "url": "api/v1/repos/stackchain/dashboard/issues/815/release-plan",
+        "method": "PATCH",
+        "body": {"milestone_id": 9, "due_date": "2026-08-31T23:59:59Z"},
+    }]
     assert result["queued"] == "queued"
     assert result["journals"] == [
         "search-today-batch", "search-later-batch", "search-release-batch",