Vercel Open Sources fx Native Coding Agent

Vercel Labs has open sourced fx, a native coding agent that began as an internal tool. fx is a harness and command line interface written in Zig for research use and for embedding inside larger systems.

The tool is distributed as a single native binary with no runtime install. The announcement states that it cold starts in 10 microseconds, has a 6.3 MiB binary, and uses single digit megabytes of memory at baseline.

fx is model and provider agnostic and supports local and cloud inference. Its core can be extended through skills, plugins, and MCP. It can be used directly through the command line or embedded as infrastructure, with structured output, editor connections, and WebAssembly support for running in a browser.

The project is released under the Apache 2.0 license. The announcement states that fx has no product telemetry, keeps sessions and usage local, and shares source code or prompts only with the inference endpoint. Vercel Labs described fx as experimental and said frequent changes should be expected.