Intermittent: /run_sse SSE connection sometimes does not close after final model response

[iamirulofficial]

Summary

When using the /run_sse endpoint in google/adk-python (v1.22.1), the SSE stream sometimes does not close after the model's final response. Other times, the connection closes properly.

Details

• Repository: google/adk-python
• Version: 1.22.1
• Model: Claude (claude-opus-4-5-20251101) via LiteLLM backend
• Endpoint: /run_sse
• Client: Browser/Angular with fetch and streaming response parsing , I am using my own UI

Observed Behavior

• The SSE connection usually closes as expected after the final text-only model message (no function call parts).
• However, in some runs (see example 1 below), the server keeps the connection open even after sending the final message. The client waits for more data forever.
• There is no explicit turnComplete or done:true signal. The client must rely on fragile heuristics which are not robust to all edge cases.

Example 1: Connection stays open

my sessions are usually 5 to 10mins long
(Final event)

{"content":{"parts":[{"text":"Fixed!  Added the missing `required` array... "}]}, ... }

— Connection does not close after this (bug)

Example 2: Connection closes as expected

(Final event)

{"content":{"parts":[{"text":"Your portfolio is ready! ..."}]}, ... }

— Connection closes as expected

What we've tried

• Attempted to detect stream completion by checking message structure, but this workaround does not work in all cases as sometimes the stream does close properly, sometimes it doesn't.
• Adding client-side completion timeouts as a hacky workaround, but this is not ideal.

Expected Behavior

• The SSE connection should ALWAYS close after the model's final response, not randomly.
• (Ideally) The server should send a clear termination signal: either closing the HTTP stream or emitting an explicit { "done": true } or similar message before closing.

Impact

• Causes frontends to hang indefinitely (no timeout event) and makes completion detection fragile.
• Client cannot reliably distinguish between server inactivity, error, or true completion.

Possible Causes (hypotheses)

• Async generator (runner.run_async()) not always completing cleanly
• Some internal ADK state or tool connections keep the generator alive on certain tool execution chains
• Lack of an explicit "done" signal makes client-side detection error-prone

Request

• Please investigate why, under some (but not all) flows, the stream stays open after the model finishes.
• Please either:
  • Fix the runner.run_async()/SSE handler to always close the HTTP response after the final turn, OR
  • Send an explicit termination/"done" event at the end so clients can handle this robustly.

Additional Context

• If helpful, I can provide full sample logs/events for both the working and non-working cases.

[adk-bot]

Notification: The author has updated the issue description. Maintainers, please review.

[klateefa]

@iamirulofficial Thanks for reporting!
Could you please try upgrading to the latest version of google adk and check if the issue still occurs? If the issue still happens after upgrading, please let us know and share any details you observe ,that will help us investigate further.
Thank you.