GPT-6 Astra broken in Cursor BYOK: dev builds relay to bridge Chat Completions and Responses API
salmoukas · reddit · 2026-09-05
A developer found gpt-6-astra unusable in Cursor with a personal OpenAI key and traced the cause via a logging relay: Cursor's BYOK path speaks Chat Completions, but OpenAI only allows function tools with reasoning for Astra via /v1/responses, and Cursor's model registry blocks the name on that path anyway.
He built a 750-line TypeScript local relay (Node 24, embedded ngrok tunnel) that translates Chat Completions requests into Responses API calls and streams back chat.completion.chunks. Aliases with effort suffixes (e.g. relay-gpt-6-astra-high) add reasoning control Cursor lacks for custom models; the real key stays in a local .env.
Caveats: requests still pass through Cursor's servers (AWS EC2), reasoning.encryptedcontent can't round-trip so Astra loses prior reasoning between turns, and Cloudflare Quick Tunnels buffer SSE so can't be used. Code is MIT-licensed on GitHub.
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