A 6MB coding agent written in Zig that starts in 10 microseconds

Most terminal AI agents feel like heavy IDEs stuffed into your prompt—fx is a 6MB binary that starts in 10 microseconds.

A new open-source project called fx caught the eye of developers on Hacker News this week. Written in Zig, it is a lightweight coding agent CLI designed to run locally or inside isolated sandboxes. The tool packs a 6.39MB binary, runs on a single-digit megabyte memory baseline, and compiles to WebAssembly. It is Apache-2.0 licensed, though the creators flag that version 0.0.3 is experimental and will change frequently.

Why it matters: Heavy terminal interfaces often swallow system resources and bloat API bills with massive system prompts. fx feels more like a standard Unix shell, using a tiny system prompt to save on token costs and improve time-to-first-token speed. Because each instance uses almost no RAM, you can pack multiple agents onto one machine.

Know this: It connects to both local and cloud models, supports plugins and MCPs, and preserves your terminal scroll history instead of repainting the screen.

Finally, an AI coding assistant that treats your RAM like it costs actual money.