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donpark/idfon-openrouter-h2-error-report.md

Created September 15, 2026 18:35
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openrouter / deepseek-v4.1-flash: 12x upstream Together h2 protocol stream errors (pi 0.85.1)
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idfon-openrouter-h2-error-report.md

OpenRouter + deepseek/deepseek-v4.1-flash: repeated HTTP/2 stream errors from upstream Together

Summary

While using openrouter serving deepseek/deepseek-v4.1-flash (API mode openai-completions) the stream repeatedly dies mid-reasoning with the OpenRouter error:

Upstream error from Together: Stream error: h2 protocol error: error reading a body from connection
  • Host: pi coding agent 0.85.1
  • Project: /Users/don/dev/idfon
  • Provider: openrouter
  • Model: deepseek/deepseek-v4.1-flash
  • Upstream named in error: Together
  • Occurrences: 12 (all on this provider/model; none on any other provider)
  • Window: 2026-09-13 19:55Z … 2026-09-14 21:37Z (UTC)

What it looks like in the client

Each occurrence is an assistant message that ends with:

  • stopReason: "error"
  • errorMessage: "Upstream error from Together: Stream error: h2 protocol error: error reading a body from connection"
  • usage: {input:0, output:0, totalTokens:0} (nothing billed/counted)
  • a partial thinking part — the model was mid-chain-of-thought when the body read failed. No text or tool-call was produced.

The connection drops after 2 s to 206 s of streaming. It is transient: the next request (usually the user typing resume) succeeds. Two user turns in the log are literally the notes resume. h2 protocol error. and another h2 protocol error..

Occurrences

timestamp (UTC) latency thinking chars at drop OpenRouter generation id pi msg id
2026-09-13T19:55:36.661Z 4s 2,402 gen-1789329332-J8dfAtCuWxeLtIShMNmu d06cac09
2026-09-13T20:04:23.101Z 37s 812 gen-1789329826-hu1BwRQ8jey0G6YWEKih 7dc71988
2026-09-13T20:11:44.996Z 206s 10,113 gen-1789330098-AkgcbsJmzBfiofHOaRJD 8817c44c
2026-09-13T20:14:41.515Z 176s 7,293 gen-1789330305-PmQZy2kV09BP4IYJbS7F 74ce8e83
2026-09-13T20:16:40.659Z 119s 5,327 gen-1789330481-Eayjct1EEB6846WZutxG db2fdfeb
2026-09-13T21:17:53.314Z 34s 9,393 gen-1789334239-P4YjD6RaCI29xEabOAI2 e36ae882
2026-09-13T21:21:15.457Z 5s 854 gen-1789334470-pay4vIASvu87oNBPmq4n d3f2dd53
2026-09-13T21:22:20.894Z 10s 5,688 gen-1789334530-iB2QfDlS04M96KQ3pBHB 40b003da
2026-09-14T02:36:58.462Z 3s 497 gen-1789353415-nW7BjE4r2EYuNawuy6lm 0846e8b5
2026-09-14T21:31:54.313Z 2s 450 gen-1789421512-NLxpwPEmfjwImnFRFiOp 5ee9b6da
2026-09-14T21:34:34.142Z 3s 446 gen-1789421671-h7dIG8cnSgmu46Ey4KOw 3c60307d
2026-09-14T21:37:40.843Z 3s 850 gen-1789421857-fK49M0NGUxNhrCgH5hP6 9226466f

Latency = error time − request start, where request start is decoded from the OpenRouter gen-<epoch>-<hash> id.

Clusters: 8 on 2026-09-13 (19:55–21:22), 1 on 2026-09-14 02:36, 3 on 2026-09-14 21:31–21:37. Failure is intermittent within a session and hits both short and long generations.

Raw record (one occurrence, trimmed)

{
  "type": "message",
  "id": "d06cac09",
  "parentId": "52addc14",
  "timestamp": "2026-09-13T19:55:36.661Z",
  "message": {
    "role": "assistant",
    "content": [{"type": "thinking", "thinking": "…partial reasoning…"}],
    "api": "openai-completions",
    "provider": "openrouter",
    "model": "deepseek/deepseek-v4.1-flash",
    "usage": {"input": 0, "output": 0, "cacheRead": 0, "cacheWrite": 0,
              "totalTokens": 0, "cost": {"total": 0}},
    "stopReason": "error",
    "timestamp": 1789329332098,
    "responseId": "gen-1789329332-J8dfAtCuWxeLtIShMNmu",
    "errorMessage": "Upstream error from Together: Stream error: h2 protocol error: error reading a body from connection"
  }
}

Provider contrast (same model id)

  • openrouter / deepseek/deepseek-v4.1-flash: 12 × the h2/Together error above. No other provider produced an h2 protocol error string in any log across the whole ~/.pi/agent/sessions tree.
  • vercel-ai-gateway / deepseek/deepseek-v4.1-flash: different failure mode, 5 × Request timed out. — no h2 errors.
  • OpenRouter errors generally: besides the 12 h2 errors, 23 × This operation was aborted and a few Provider finish_reason: error, Stream ended without finish_reason, Upstream idle timeout exceeded, 503 status code (no body) / terminated.

Log locations

  • /Users/don/.pi/agent/sessions/--Users-don-dev-idfon--/2026-09-13T19-46-52-450Z_01a09c4e-e9a2-73bd-af78-a5ed436b2b43.jsonl (8)
  • /Users/don/.pi/agent/sessions/--Users-don-dev-idfon--/2026-09-14T21-24-45-662Z_01a0a1ce-e3dd-71f2-9b64-72971523d84d.jsonl (3)
  • /Users/don/.pi/agent/sessions/--Users-don-dev-idfon--/2026-09-14T02-20-57-201Z_01a09db7-b3f0-76c0-89ce-d88de2c6df74.jsonl (1)

Suggested minimal repro

Send a long-thinking, tool-using request to openrouter with deepseek/deepseek-v4.1-flash (reasoning streamed; upstream routes to Together). Observe the SSE body abort mid-stream with Upstream error from Together: Stream error: h2 protocol error: error reading a body from connection. The OpenRouter generation ids above can be looked up directly.

@j-r-andrews

j-r-andrews commented Sep 16, 2026

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I was able to reproduce this issue with openrouter and deepseek-v4.1-flash. I didn't set out to do it, but it was occurring during development work I was doing in Rust.

Upstream error from Together: Stream error: h2 protocol error: error reading a body from connection

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