Skip to content

OpenCode (opencode)

OpenCode is an open-source agentic coding CLI by Anomaly that supports multiple model providers (OpenAI, Anthropic, Google, and others) via a unified interface.

Install

npm install -g @opencode/cli

Authenticate

OpenCode connects to whichever model provider you configure. Set the relevant API key:

# OpenAI models
export OPENAI_API_KEY=sk-...

# Anthropic models
export ANTHROPIC_API_KEY=sk-ant-...

# Google models
export GOOGLE_API_KEY=...

Or configure a provider in ~/.config/opencode/opencode.jsonc. See the OpenCode docs for the full list of supported providers.

Configure in millstone

[millstone]
cli = "opencode"

Or target a specific role:

[millstone]
cli          = "claude"
cli_reviewer = "opencode"

Notes

  • millstone invokes opencode run <prompt> --format json -m <model>, which runs OpenCode non-interactively and requests newline-delimited JSON event output for parsing.
  • The default model is opencode/trinity-large-preview-free. Pass --model to millstone to override: millstone --model openai/gpt-5.
  • Structured output appends a JSON schema instruction to the prompt, since OpenCode does not natively support --json-schema.
  • Session resume uses opencode run --session <session_id> <follow_up_prompt>.

Further reading