Fastest CLI

Fastest is an agentic coding CLI that runs with the fast command and the codex compatibility alias. The package does not ship a default provider or default model; configure the provider and model you want in your own Codex config or .fast/settings.json.

Fastest is based on the Apache-2.0 licensed open-source Codex codebase from OpenAI. This repository keeps the upstream LICENSE and NOTICE files intact. If you redistribute Fastest builds, keep those files with your distribution.

Install

npm install -g fastest-cli@latest

Run the interactive TUI:

fast

Run a direct prompt:

fast "inspect this repository and fix the failing tests"

Run non-interactively:

fast exec "summarize the current diff"

Configuration

Fastest uses ~/.fast as its home directory so its config, auth, sessions, logs, and .env stay isolated from Codex ~/.codex.

Fastest reads the native TOML configuration from ~/.fast/config.toml and also supports a compatibility file at .fast/settings.json for teams already using that JSON shape.

Supported compatibility locations:

• ~/.fast/settings.json
• <repo>/.fast/settings.json

Fastest home-scoped files live under ~/.fast/, for example:

• ~/.fast/config.toml
• ~/.fast/.env
• ~/.fast/auth.json and other auth/session state
• ~/.fast/log/

Project settings override home settings.

Example .fast/settings.json:

{
  "llm": {
    "provider": "openai",
    "default_model": "gpt-5.3-codex",
    "effort": "high"
  }
}

You can also define custom provider and model entries in .fast/settings.json. The compatibility layer can provide the active provider, a default model, and a custom model catalog when present, but the binary itself does not ship a Fastest-specific model catalog.

Providers

Fastest supports multiple providers from one CLI surface:

• ollama
• openai
• anthropic
• litellm

Use whichever provider and model your config points to.

Repo Instructions

Fastest uses AGENTS.md as the primary project instruction file.

Common locations:

• repo-root AGENTS.md
• nested AGENTS.md files for subdirectories

Development

Install dependencies:

pnpm install

Build TypeScript support files:

pnpm run build

Build the Rust CLI:

cd codex-rs
cargo build -p codex-cli

Verify the TUI harness:

pnpm run verify:tui

License

Fastest is distributed under Apache-2.0. Because it is based on the open-source Codex codebase, keep LICENSE and NOTICE with redistributed builds.