diff --git a/api/chat/_stream.py b/api/chat/_stream.py
index dcb7f52ab..921e8b2c2 100644
--- a/api/chat/_stream.py
+++ b/api/chat/_stream.py
@@ -165,13 +165,21 @@ async def respond_stream(self, prompt: str) -> AsyncIterator[str]:
         )
 
         async for chunk in response:
+            # Responses API event shape
+            if getattr(chunk, "type", "") == "response.output_text.delta":
+                delta = getattr(chunk, "delta", None)
+                if delta:
+                    yield delta
+                continue
+
+            # Chat Completions chunk shape
+            choices = getattr(chunk, "choices", None)
             if (
-                chunk.choices
-                and chunk.choices[0].delta is not None
-                and chunk.choices[0].delta.content is not None
+                choices
+                and choices[0].delta is not None
+                and choices[0].delta.content is not None
             ):
-                yield chunk.choices[0].delta.content
-
+                yield choices[0].delta.content
 
 class OpenAIChatStreamer(_OpenAICompatStreamer):
     provider = "openai"