From 1a4d3e4a375a0aecdaed54793a19848f66c646a0 Mon Sep 17 00:00:00 2001
From: Prashanth1602 <prashanthsurapaneni123@gmail.com>
Date: Mon, 27 Apr 2026 15:23:29 +0530
Subject: [PATCH] Fix: preserve stream_item_type when using include_router for
 SSE routes

---
 fastapi/routing.py |  8 ++++++++
 tests/test_sse.py  | 17 +++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/fastapi/routing.py b/fastapi/routing.py
index 36acb6b89d..8275d58b2d 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -1794,6 +1794,14 @@ class APIRouter(routing.Router):
                         self.strict_content_type,
                     ),
                 )
+                new_route = self.routes[-1]
+                if (
+                    isinstance(new_route, APIRoute)
+                    and isinstance(route, APIRoute)
+                    and getattr(route, "stream_item_type", None) is not None
+                ):
+                    new_route.stream_item_type = route.stream_item_type
+                    
             elif isinstance(route, routing.Route):
                 methods = list(route.methods or [])
                 self.add_route(
diff --git a/tests/test_sse.py b/tests/test_sse.py
index 6dfec61838..e86b3970ee 100644
--- a/tests/test_sse.py
+++ b/tests/test_sse.py
@@ -264,6 +264,23 @@ def test_sse_on_router_included_in_app(client: TestClient):
     ]
     assert len(data_lines) == 2
 
+def test_include_router_copies_stream_item_type():
+    sub_router = APIRouter()
+
+    @sub_router.get("/stream_item_type", response_class=EventSourceResponse)
+    async def stream_item_type_route() -> AsyncIterable[Item]:
+        yield items[0]
+
+    assert getattr(sub_router.routes[-1], "stream_item_type", None) == Item
+
+    main_app = FastAPI()
+    main_app.include_router(sub_router)
+
+    route = next(r for r in main_app.routes
+     if r.path == "/stream_item_type")
+    assert getattr(route, "stream_item_type", None) == Item
+
+
 
 # Keepalive ping tests