Claude Opus 5.5 can now rebuild real programs from scratch — 18.5% on ProgramBench, up from 0% in May

Claude Opus 5.5 (xhigh) now resolves 18.5% of ProgramBench's 200 from-scratch rebuild tasks, up from 0% when every model failed at the benchmark's May launch, according to Jack Clark's Import AI newsletter of Oct 26. The benchmark asks models to rewrite programs such as SQLite, FFmpeg and ripgrep from a compiled binary and its documentation.

According to Jack Clark's Import AI Oct 26 , Claude Opus 5.5 xhigh now resolves 18.5% of ProgramBench's 200 from-scratch rebuild tasks — rewriting programs like SQLite, FFmpeg and ripgrep from a compiled binary and its docs. That is up from 0% when every model failed at the benchmark's May launch