Other harnesses

Any client that lets you set a custom baseURL works with cmx. The contract is three things:

1. baseURL → http://127.0.0.1:17322
2. cmx-provider header → the upstream provider name from cmx config
3. cmx-harness header → a label for the UI (any string)

Auth stays where it belongs: your harness sends its own Authorization / API key, cmx forwards it to the upstream untouched.

Endpoints

Client type	Path	Format
OpenAI-style	POST /v1/chat/completions	chat.completion objects
Anthropic-style	POST /v1/messages	message objects

Streaming (SSE) and non-streaming are both supported for both dialects. Unknown paths are passed through to the upstream unchanged.

Session attribution

cmx groups requests into sessions by looking for, in order:

• cmx-session-id
• x-opencode-session
• x-session-id
• x-claude-session-id

If none is present, it falls back to a fingerprint of model + system prompt + first message — good enough for most CLI agents, but an explicit header is more reliable.

Claude Code

Claude Code honors ANTHROPIC_BASE_URL (point it at http://127.0.0.1:17322) and sends x-claude-session-id, so it works without extra headers. Define an anthropic provider in cmx config and route with cmx-provider: anthropic.

What cmx does to traffic

• Adds <cmx-id-*> markers to older messages (harmless text to the model)
• Adds the compress tool if not already present
• Strips compress tool calls from responses before the harness sees them
• Occasionally appends a small <cmx-system-reminder> nudge to the last user message when context is large
• Never modifies stored session history — rewrites happen only in the proxied request