OpenCode Go requires `x-opencode-session` HTTP header from 06/09/2026

OpenCode Go began sending automated emails notifying affected users a few days ago. The email they sent might have ended up in the spam folder if you use gmail. Starting 6th of September, requests to OpenCode Go will fail if they didn’t contain the session header. The required header is pretty straight forward: {'x-opencode-session': '<stable-id-per-conversation>'} They require this header to better manage tokens caching on third party harnesses/services. One specific affected harness is Hermes, it needs to be upgraded past v0.21.0 to include that header. DeepSeek Harness is another affected one, but it seems opencode updated their logic on their end to also support the deepseek-specific session ids based on this post [https://github.com/deepseek-ai/deepseek-harness/discussions/5495] while still requiring the header so the fix might be temporary.