A tweet by Spanish-language developer influencer @midudev on the night of August 20 (local time), introducing "Vercel released fx, a Claude Code alternative," drew more than 50,000 views. To judge whether it was exaggerated, we opened fx.sh and GitHub (vercel-labs/fx) directly and checked the specs.
6MB, 10 microseconds: fx's actual specs
fx.sh describes fx as a "Tiny, open, native coding agent." It's written in Zig, the executable is 6.39 MiB (about 6MB), cold start is 10 microseconds, and the license is Apache-2.0. It runs without telemetry and isn't tied to any particular model, so you can plug in whatever LLM you want.
Who called it a "Claude Code alternative"?
The phrase "Claude Code alternative" appears in neither Vercel's official announcement nor the InfoQ report. If anything, in Vercel's official materials Claude Code is treated as a partner tool integrated with AI Gateway. The "alternative" framing is closer to a nickname that developers in the community naturally attached after the announcement.
GLM 5.2 is free, but miss the conditions and you get billed
The same tweet said "GLM 5.2 is free through August 27." Checking Vercel's official changelog, this benefit comes with the conditions "for eve agents only, via Blackbox AI, through August 27." Whether these conditions apply to fx itself isn't stated in the official documentation. In fact, one user in the replies reported "it wasn't free; I got charged," and midudev answered, "You need to set Blackbox AI as the provider to get $0." Unless you check your provider settings yourself, you could get a bill you didn't expect.