diff --git a/backend/packages/harness/deerflow/runtime/runs/worker.py b/backend/packages/harness/deerflow/runtime/runs/worker.py
index e3543c15ae..87f2ead9bf 100644
--- a/backend/packages/harness/deerflow/runtime/runs/worker.py
+++ b/backend/packages/harness/deerflow/runtime/runs/worker.py
@@ -1395,16 +1395,11 @@ async def run_agent(
                         graph_input["goal"] = Overwrite(copy.deepcopy(current_values.get("goal")))
                     graph_input["goal_outcome"] = None
 
-        # Capture the effective (resolved) model name from the agent's metadata.
-        # _resolve_model_name in agent.py may return the default model if the
-        # requested name is not in the allowlist — this update ensures the
-        # persisted model_name reflects the actual model used.
-        if record.model_name is not None:
-            resolved = getattr(agent, "metadata", {}) or {}
-            if isinstance(resolved, dict):
-                effective = resolved.get("model_name")
-                if effective and effective != record.model_name:
-                    await run_manager.update_model_name(record.run_id, effective)
+        # Persist the model assembly resolved — the default when the request
+        # named none, or a fallback when the requested model is unavailable —
+        # so the stored model_name reflects the actual model used (#3109).
+        if effective_model and effective_model != record.model_name:
+            await run_manager.update_model_name(record.run_id, effective_model)
 
         # 4. Attach checkpointer and store
         if checkpointer is not None:
diff --git a/backend/tests/test_worker_langfuse_metadata.py b/backend/tests/test_worker_langfuse_metadata.py
index cda608efef..92e04b22eb 100644
--- a/backend/tests/test_worker_langfuse_metadata.py
+++ b/backend/tests/test_worker_langfuse_metadata.py
@@ -210,6 +210,66 @@ async def test_run_agent_tags_the_effective_model(monkeypatch, requested_model):
     assert "model:missing-model" not in tags
 
 
+class _ModelNameRecordingRunManager(_FakeRunManager):
+    def __init__(self) -> None:
+        self.model_name_updates: list[tuple[str, str | None]] = []
+
+    async def update_model_name(self, run_id: str, model_name: str | None) -> None:
+        self.model_name_updates.append((run_id, model_name))
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    ("requested_model", "expected_updates"),
+    [
+        (None, [("run-persist-model", "actual-model")]),
+        ("missing-model", [("run-persist-model", "actual-model")]),
+        ("actual-model", []),
+    ],
+)
+async def test_run_agent_persists_the_effective_model(monkeypatch, requested_model, expected_updates):
+    """The run record stores the model that ran, including when none was requested (#3109)."""
+    from deerflow.agents.lead_agent import agent as lead_agent_module
+    from deerflow.config.app_config import AppConfig
+    from deerflow.config.model_config import ModelConfig
+    from deerflow.config.sandbox_config import SandboxConfig
+
+    fake_agent = _FakeAgent()
+    app_config = AppConfig(
+        models=[ModelConfig(name="actual-model", model="actual-model", use="langchain_openai:ChatOpenAI")],
+        sandbox=SandboxConfig(use="deerflow.sandbox.local:LocalSandboxProvider"),
+    )
+    monkeypatch.setattr(lead_agent_module, "create_chat_model", lambda **kwargs: object())
+    monkeypatch.setattr(lead_agent_module, "create_agent", lambda **kwargs: fake_agent)
+
+    def agent_factory(config):
+        return lead_agent_module.assemble_lead_agent(config, app_config=app_config)
+
+    record = RunRecord(
+        run_id="run-persist-model",
+        thread_id="thread-persist-model",
+        assistant_id="lead-agent",
+        status=RunStatus.pending,
+        on_disconnect=DisconnectMode.cancel,
+        model_name=requested_model,
+    )
+    record.abort_event = asyncio.Event()
+    run_manager = _ModelNameRecordingRunManager()
+
+    await run_agent(
+        _FakeBridge(),
+        run_manager,
+        record,
+        ctx=RunContext(checkpointer=None, app_config=app_config),
+        agent_factory=agent_factory,
+        graph_input={"messages": []},
+        config={"configurable": {"thread_id": record.thread_id, "model_name": requested_model}},
+    )
+
+    assert fake_agent.captured_config is not None, "astream was not invoked"
+    assert run_manager.model_name_updates == expected_updates
+
+
 @pytest.mark.asyncio
 async def test_run_agent_uses_context_user_id_over_contextvar(monkeypatch):
     """A run carrying ``context.user_id`` traces to that user, not the contextvar.