Jane Street

On the author's own laptop, firing one updated node costs about 30 nanoseconds, the benchmark for a graph Jane Street now uses to price portfolio risk in real time.

A Notion engineer added that the whole pattern already ships under yet another name, 'signals,' inside Vue, Svelte, Angular, and React tooling. Not everyone was impressed: a quant said he'd built the identical system for his fund seven years ago.

Jane Street argues the value of programming is shifting from writing code to verifying it: when GenAI produces tens of thousands of lines no one can review, formal specs and proofs become the affordable way to be certain. They point to OxCaml, seL4, Dafny and TLA+ as the industrial track.

A reverse engineer flagged the asterisk: seL4 is formally verified and still shipped gnarly bugs. The deeper crack came from a commenter who keeps trying for years: a formal spec is just 'the same implementation written a different way' and can carry the same bug.