diff --git a/python/packages/ag-ui/README.md b/python/packages/ag-ui/README.md
index 692ebcfd06..120f0d90b0 100644
--- a/python/packages/ag-ui/README.md
+++ b/python/packages/ag-ui/README.md
@@ -335,7 +335,10 @@ A frontend can then hydrate the latest stored snapshot for the scoped thread:
 
 Endpoint configuration requires `snapshot_scope_resolver` whenever a snapshot store is configured, including when
 the store is already set on a pre-wrapped `AgentFrameworkAgent` or `AgentFrameworkWorkflow`. The resolver returns
-the application-defined Snapshot Scope used with the AG-UI Thread id as the storage key.
+the application-defined Snapshot Scope used with the AG-UI Thread id as the storage key. When using
+`AgentFrameworkWorkflow(workflow_factory=...)`, the same resolver also scopes the in-memory workflow cache even
+without a snapshot store; provide it in multi-user deployments so two users who submit the same `threadId` do not
+share a live `Workflow` instance.
 
 For hosted agents, request Shared State is also available through `AgentSession.state` during that run, whether or
 not snapshot persistence is configured. Request values are untrusted per-run context: they overlay ordinary restored
diff --git a/python/packages/ag-ui/agent_framework_ag_ui/_endpoint.py b/python/packages/ag-ui/agent_framework_ag_ui/_endpoint.py
index d1b184c964..5486802d64 100644
--- a/python/packages/ag-ui/agent_framework_ag_ui/_endpoint.py
+++ b/python/packages/ag-ui/agent_framework_ag_ui/_endpoint.py
@@ -111,7 +111,8 @@ def add_agent_framework_fastapi_endpoint(
         snapshot_store: Optional AG-UI Thread Snapshot store. Snapshot persistence is opt-in and requires an
             explicit Snapshot Scope resolver.
         snapshot_scope_resolver: Optional resolver for the application-defined Snapshot Scope. Required whenever
-            a snapshot store is configured because an AG-UI Thread id is not an authorization boundary.
+            a snapshot store is configured because an AG-UI Thread id is not an authorization boundary. Also scopes
+            in-memory workflow_factory instances when provided without a snapshot store.
         keepalive_seconds: Endpoint SSE keepalive interval in seconds. Defaults to 15. Positive values emit fixed
             SSE comments while the stream is open. None disables keepalive and preserves the non-keepalive response
             path. Keepalive comments are transport traffic and do not change AG-UI events.
@@ -150,15 +151,13 @@ async def agent_endpoint(request_body: AGUIRequest) -> Response:
         """
         try:
             input_data = request_body.model_dump(exclude_none=True)
-            snapshot_persistence_active = False
+            snapshot_persistence_active = _get_snapshot_store(protocol_runner) is not None
             if snapshot_scope_resolver is not None:
                 snapshot_scope = snapshot_scope_resolver(request_body)
                 if isawaitable(snapshot_scope):
                     snapshot_scope = await snapshot_scope
                 input_data[_APPROVAL_SCOPE_INPUT_KEY] = snapshot_scope
-                if _get_snapshot_store(protocol_runner) is not None:
-                    input_data[_SNAPSHOT_SCOPE_INPUT_KEY] = snapshot_scope
-                    snapshot_persistence_active = True
+                input_data[_SNAPSHOT_SCOPE_INPUT_KEY] = snapshot_scope
             if default_state:
                 if snapshot_persistence_active:
                     # Defer default application to the runner so defaults only fill keys
diff --git a/python/packages/ag-ui/agent_framework_ag_ui/_workflow.py b/python/packages/ag-ui/agent_framework_ag_ui/_workflow.py
index d558a65a30..27b3f4fa62 100644
--- a/python/packages/ag-ui/agent_framework_ag_ui/_workflow.py
+++ b/python/packages/ag-ui/agent_framework_ag_ui/_workflow.py
@@ -248,8 +248,9 @@ def __init__(
         self.workflow = workflow
         self._workflow_factory = workflow_factory
         # Cache keyed by (snapshot_scope, thread_id): the Snapshot Scope is the
-        # authorization boundary, so the same thread id under different scopes
-        # must never share an in-memory workflow instance.
+        # authorization boundary for both snapshots and in-memory workflow_factory
+        # instances, so the same thread id under different scopes must never share
+        # mutable workflow state.
         self._workflow_by_thread: dict[tuple[str | None, str], Workflow] = {}
         self.name = name if name is not None else getattr(workflow, "name", "workflow")
         self.description = description if description is not None else getattr(workflow, "description", "")
diff --git a/python/packages/ag-ui/tests/ag_ui/test_endpoint.py b/python/packages/ag-ui/tests/ag_ui/test_endpoint.py
index eb060c9315..303a307d91 100644
--- a/python/packages/ag-ui/tests/ag_ui/test_endpoint.py
+++ b/python/packages/ag-ui/tests/ag_ui/test_endpoint.py
@@ -40,6 +40,7 @@
 from fastapi.testclient import TestClient
 
 from agent_framework_ag_ui import (
+    AGUIRequest,
     AGUIThreadSnapshot,
     InMemoryAGUIThreadSnapshotStore,
     add_agent_framework_fastapi_endpoint,
@@ -5160,3 +5161,75 @@ def factory(thread_id: str) -> Any:
 
     runner.clear_thread_workflow("thread-1")
     assert runner._resolve_workflow("thread-1", "tenant-b") is not workflow_b
+
+
+async def test_workflow_factory_cache_is_scoped_by_resolver_without_snapshot_store():
+    """Snapshot Scope resolver scopes live workflow_factory instances even without snapshot persistence."""
+
+    @executor(id="responder")
+    async def responder(message: Any, ctx: WorkflowContext[Any, Any]) -> None:
+        del message
+        await ctx.yield_output("Workflow response")
+
+    created_workflows: list[Any] = []
+
+    def factory(thread_id: str) -> Any:
+        del thread_id
+        workflow = WorkflowBuilder(start_executor=responder).build()
+        created_workflows.append(workflow)
+        return workflow
+
+    def resolve_scope(request: AGUIRequest) -> str:
+        forwarded_props = request.forwarded_props
+        assert forwarded_props is not None
+        tenant = forwarded_props["tenant"]
+        assert isinstance(tenant, str)
+        return tenant
+
+    app = FastAPI()
+    runner = AgentFrameworkWorkflow(workflow_factory=factory)
+    add_agent_framework_fastapi_endpoint(
+        app,
+        runner,
+        path="/workflow",
+        snapshot_scope_resolver=resolve_scope,
+    )
+    client = TestClient(app)
+
+    response_a = client.post(
+        "/workflow",
+        json={
+            "thread_id": "thread-1",
+            "messages": [{"role": "user", "content": "Hello tenant A"}],
+            "forwardedProps": {"tenant": "tenant-a"},
+        },
+    )
+    response_b = client.post(
+        "/workflow",
+        json={
+            "thread_id": "thread-1",
+            "messages": [{"role": "user", "content": "Hello tenant B"}],
+            "forwardedProps": {"tenant": "tenant-b"},
+        },
+    )
+    response_a_again = client.post(
+        "/workflow",
+        json={
+            "thread_id": "thread-1",
+            "messages": [{"role": "user", "content": "Hello tenant A again"}],
+            "forwardedProps": {"tenant": "tenant-a"},
+        },
+    )
+
+    assert response_a.status_code == 200
+    assert response_b.status_code == 200
+    assert response_a_again.status_code == 200
+    assert len(created_workflows) == 2
+    assert (
+        runner._resolve_workflow("thread-1", "tenant-a")  # pyright: ignore[reportPrivateUsage]
+        is created_workflows[0]
+    )
+    assert (
+        runner._resolve_workflow("thread-1", "tenant-b")  # pyright: ignore[reportPrivateUsage]
+        is created_workflows[1]
+    )