Tachyon docs

Tachyon is a terminal coding agent that runs on your keys, your models, and your machine. These docs cover installing it, pointing it at a provider, and keeping it on a leash.

What Tachyon is

Tachyon is a single binary that puts a coding agent in your terminal. It reads and edits files, runs commands, searches the web, and drives long multi-step work — inside whatever repository you launch it from.

It is bring-your-own-key. You supply credentials for a model provider and talk to that provider directly; your code is not proxied through a hosted service. That also means the tool itself is free to run — you pay your provider, nobody else.

  • 130+ providers via the models.dev catalogue — Anthropic, OpenAI, Google, Groq, local Ollama, or anything OpenAI-compatible.
  • OS-level sandboxing — bwrap on Linux, Seatbelt on macOS, Docker anywhere, with network denied by default.
  • Plan mode that hard-blocks mutating tools while the agent researches, rather than politely asking it not to edit.
  • Subagents, hooks, skills, and MCP — including auto-import of existing Claude Code and OpenCode MCP config.

How a turn runs

Understanding the turn loop explains most of Tachyon's behaviour. Every message you send walks the same path:

  1. The UserPromptSubmit hook fires and can rewrite or block the prompt.
  2. If the session has exceeded 75% of the model's context window, it is compacted into a structured summary first.
  3. The tool registry is composed: core tools, plus MCP-contributed and plugin tools.
  4. The system prompt is assembled from your project memory, skills, and effort level.
  5. The model streams. Every tool call passes through the permission gate before it runs.
  6. The Stop hook fires when the turn finishes.

The permission gate in step 5 is the part worth internalising — it is what stands between a confident model and your filesystem. See Permissions & sandboxing.

Start here

If you have never run Tachyon, the fastest path is four commands:

bash
curl -fsSL https://tachyon.feyncode.com/install.sh | sh
tachyon login anthropic
cd ~/your-project
tachyon