diff --git a/fastapi/routing.py b/fastapi/routing.py
index e2c83aa7b3..f65478c978 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -836,10 +836,11 @@ class APIRoute(routing.Route):
         generate_unique_id_function: Callable[["APIRoute"], str]
         | DefaultPlaceholder = Default(generate_unique_id),
         strict_content_type: bool | DefaultPlaceholder = Default(True),
+        stream_item_type: Any | None = None,
     ) -> None:
         self.path = path
         self.endpoint = endpoint
-        self.stream_item_type: Any | None = None
+        self.stream_item_type: Any | None = stream_item_type
         if isinstance(response_model, DefaultPlaceholder):
             return_annotation = get_typed_return_annotation(endpoint)
             if lenient_issubclass(return_annotation, Response):
@@ -1360,6 +1361,7 @@ class APIRouter(routing.Router):
         generate_unique_id_function: Callable[[APIRoute], str]
         | DefaultPlaceholder = Default(generate_unique_id),
         strict_content_type: bool | DefaultPlaceholder = Default(True),
+        stream_item_type: Any | None = None,
     ) -> None:
         route_class = route_class_override or self.route_class
         responses = responses or {}
@@ -1409,6 +1411,7 @@ class APIRouter(routing.Router):
             strict_content_type=get_value_or_default(
                 strict_content_type, self.strict_content_type
             ),
+            stream_item_type=stream_item_type,
         )
         self.routes.append(route)
 
@@ -1789,6 +1792,7 @@ class APIRouter(routing.Router):
                         router.strict_content_type,
                         self.strict_content_type,
                     ),
+                    stream_item_type=route.stream_item_type,
                 )
             elif isinstance(route, routing.Route):
                 methods = list(route.methods or [])
diff --git a/tests/test_sse.py b/tests/test_sse.py
index 6dfec61838..b58e547353 100644
--- a/tests/test_sse.py
+++ b/tests/test_sse.py
@@ -96,6 +96,18 @@ async def stream_events():
     yield {"msg": "world"}
 
 
+@router.get("/events-typed", response_class=EventSourceResponse)
+async def stream_events_typed() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
+@router.get("/events-jsonl")
+async def stream_events_jsonl() -> AsyncIterable[Item]:
+    for item in items:
+        yield item
+
+
 app.include_router(router, prefix="/api")
 
 
@@ -265,6 +277,49 @@ def test_sse_on_router_included_in_app(client: TestClient):
     assert len(data_lines) == 2
 
 
+def test_sse_router_typed_openapi_schema(client: TestClient):
+    """Typed SSE endpoint on a router should preserve itemSchema with contentSchema."""
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    paths = response.json()["paths"]
+    sse_response = paths["/api/events-typed"]["get"]["responses"]["200"]
+    assert sse_response == {
+        "description": "Successful Response",
+        "content": {
+            "text/event-stream": {
+                "itemSchema": {
+                    "type": "object",
+                    "properties": {
+                        "data": {
+                            "type": "string",
+                            "contentMediaType": "application/json",
+                            "contentSchema": {"$ref": "#/components/schemas/Item"},
+                        },
+                        "event": {"type": "string"},
+                        "id": {"type": "string"},
+                        "retry": {"type": "integer", "minimum": 0},
+                    },
+                    "required": ["data"],
+                }
+            }
+        },
+    }
+
+
+def test_jsonl_router_typed_openapi_schema(client: TestClient):
+    """Typed JSONL endpoint on a router should preserve itemSchema."""
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+    paths = response.json()["paths"]
+    jsonl_response = paths["/api/events-jsonl"]["get"]["responses"]["200"]
+    assert jsonl_response == {
+        "description": "Successful Response",
+        "content": {
+            "application/jsonl": {"itemSchema": {"$ref": "#/components/schemas/Item"}}
+        },
+    }
+
+
 # Keepalive ping tests