Vercel Labs has released fx as an open-source coding agent designed to be embedded in developer tools and automation. Written in Zig, it can run as a command-line program, a library or a WebAssembly module instead of taking over the terminal with a persistent interface.
Vercel reports a 6.3 MiB native binary, single-digit-megabyte baseline memory use and a 10-microsecond cold start, though those figures have not been independently verified. Structured output lets CI jobs and scripts parse responses, while editors can connect through the Agent Client Protocol. The libfx package exposes the same engine to JavaScript.
The project now supports Vercel AI Gateway, ChatGPT and Grok subscriptions, plus OpenAI-compatible endpoints such as Ollama and OpenRouter. That broader provider support followed early questions about whether an agent initially routed through Vercel’s own gateway was truly model-agnostic.
fx remains pre-1.0 and changes can break compatibility: checkpoints from a newer libfx version may not open in older releases. Its name also conflicts with an established terminal JSON viewer that already owns the Homebrew formula. Developers considering it for embedded workflows need to track migrations and packaging decisions rather than treating the current interface as stable.