According to CoinMeta, Vercel Labs has open-sourced the internally used Coding Agent tool fx. This tool is written in Zig, with a total program size of about 6.4 MiB. The cold startup time is only 10 microseconds, and the basic memory usage is in single digits of MB. fx supports integration with different models, skills, mcp and sub-agent, and can be integrated with editors through acp. It can even be run directly in web pages without the need for users to install local programs. fx does not collect additional usage data; session and usage records are stored locally by default. If a local model is used and networking is disabled, it can also operate completely offline. This project is still in the experimental stage and is suitable for running a large number of agent simultaneously for model testing.