btw it's open source

https://github.com/Slokh/anoncast

Does this require a server? Is there a way to build it without a server, by making the farcaster account itself a smart contract that accepts a zk proof as its signature scheme?

Vitalik, you should also try @33bits by @fastfourier.eth, it's open source: https://github.com/33bits-xyz and 1 year old.

Full-time builder. @pimlico | @33bits | farcaster-solidity | x.com/potekhin_sergey. Zero-knowledge and asynchronous transactions evangelist.

Foster open dialogues on Farcaster | Zk prove your fid & cast privately | Cast: https://33bits.xyz