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Claude Code speaks the Anthropic Messages API. Morph serves that format at /v1/messages for every open-source chat model, so Claude Code runs on Morph with four env vars. You need a Morph API key.

Run Claude Code on a Morph model

ANTHROPIC_MODEL remaps sonnet/opus. ANTHROPIC_SMALL_FAST_MODEL remaps haiku — the background calls for titles and summaries.
Or persist it in ~/.claude/settings.json:
Read, Edit, Write, Bash, and Grep run through the standard tool_use / tool_result loop. Streaming, system prompts, and cache_control work as Anthropic documents them; model reasoning arrives as thinking blocks. Model IDs are on the Open Source Models page — morph-glm52-744b and morph-qwen35-397b are cheaper alternatives to K3. Codex and per-task model routing: Claude Code & Codex.

Add Fast Apply and WarpGrep as tools

Independent of which model runs the loop, the Morph MCP server gives Claude Code edit_file (10,500 tok/s merges) and codebase_search:
Then tell Claude when to reach for them:

Troubleshooting

401 on every request. Claude Code sends ANTHROPIC_AUTH_TOKEN as a bearer token; ANTHROPIC_API_KEY also works. Both go to the same Morph key — don’t leave an Anthropic key in either variable. Model not found. Use a Morph model ID (morph-kimik3), not claude-sonnet-4-6. Morph serves its own models, not Anthropic’s. Claude isn’t calling edit_file. Confirm the MCP server is connected with /mcp, and that the instructions above landed in ~/.claude/CLAUDE.md.