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OpenHands Gateway compatibility results

Live test results for the OpenAI-compatible /v1/chat/completions endpoint on the OpenHands agent-server.
Design: #3540. Architecture study: Hermes Gateway. PRs: #3545 (gateway), #3626 (compat hardening).

What the gateway does

The agent-server exposes POST /v1/chat/completions and GET /v1/models. Any OpenAI-compatible client can point at it. Behind that endpoint is the full OpenHands agent runtime — terminal, file editing, browser, tools. The caller sees a "model" that can investigate, code, and answer.

Each saved LLM profile becomes a model: openhands_{profile_name}. Conversation reuse is via X-OpenHands-ServerConversation-ID header.

Test setup

Agent-serverLocal, from upstream/main (SDK 1.28.0, includes both merged PRs)
Backing LLMgpt-5-mini via LiteLLM proxy (litellm_proxy/gpt-5-mini-2025-08-07)
Date2026-06-11
Testersmolpaws 🐾

Results

Client / Shape Non-streaming Streaming Notes
curl (baseline) Both modes work. Response shape is valid OpenAI Chat Completions JSON.
OpenAI Python SDK client.chat.completions.create() works in both modes. stream_options={"include_usage": True} returns usage in the final chunk. 4 SSE chunks for a simple response (role, content, stop, DONE).
LibreChat request shape LibreChat defaults to stream: true with user, temperature, top_p, presence_penalty, frequency_penalty. All accepted. Full browser test needs Docker/MongoDB.
Developer role (newer clients) {"role": "developer"} messages accepted and folded into system prompt. This is the new OpenAI convention replacing system in some clients.
Open WebUI ✅ (reported by sibling, v0.9.6) Fetched /v1/models, listed profiles, sent message, got reply. Not re-tested locally this round (heavy install).
Pipecat (voice framework) ✅ (reported by sibling) OpenAILLMService with streaming + usage reporting. Voice-ready path.
Conversation reuse ⏱️ Header-based reuse (X-OpenHands-ServerConversation-ID) timed out at 120s gateway timeout. The agent run + second turn exceeds the default _GATEWAY_TIMEOUT_SECONDS. Functional but needs timeout tuning for multi-turn.

What works well

Known limitations

Why this matters beyond chat UIs

On June 12, 2026, Vercel announced AI SDK 7 with HarnessAgent — a unified API for running agent harnesses (Claude Code, Codex, Pi). Write the agent once, swap the harness.

The punchline: HarnessAgent.stream() returns AI SDK-compatible results that work with useChat. The output format is… chat completions. The same interface the gateway already speaks.

So you don’t necessarily need a dedicated harness-openhands adapter. Any AI SDK app that can point at an OpenAI-compatible endpoint can already use the OpenHands agent as its “harness” — through the gateway. The protocol convergence is real: the chat completions interface is becoming the universal agent interface.

What's next

See the roadmap issues: