One Code

One Code runs the whole Claude Code workflow (subagents, git worktrees, auto mode, ultracode workflows, plan mode) on the model of your choice. It is a companion to Claude Code: keep Claude Code for the work that earns its best model, and reach for One Code whenever a cheaper or different model fits the job.

What it does:

• Any model, any provider. Anthropic, OpenAI, Gemini, or a local model. Bring your own and switch mid-session with /model.
• Mix providers in a single session. The parent and each subagent choose their own model and provider, so an ultracode workflow can fan out to a cheap tier while the parent stays on a frontier model. A single-gateway setup cannot do this.
• Your Claude Code setup runs unchanged. CLAUDE.md, .claude/commands, .claude/skills, .claude/agents, .mcp.json, plugins, and permission rules are all picked up as they are.
• Capability-tiered prompting. A weaker model gets more guidance, not less.
• Built as a pi package, not a fork, so it is extensible with your own extensions, themes, and settings.
• Free and open source (MIT).

The features that make Claude Code good (the steering, the permission gate, the context management) live in the harness, not the model. One Code brings all of them across. It is the practical companion to my Harness Engineering 101 series, which builds these ideas up from first principles.