Opus 5.5 and Fable 5.1 both port HAProxy from C to Rust, Opus 5.5 faster and cheaper

Boris Cherny @bchernyOriginally posted 2026.09.23

Open original on X

Opus 5.5 is a really good model. It's been my daily driver the last few weeks. We had Opus 5.5 and Fable 5.1 each port HAProxy from C to Rust. Both passed nearly all of HAProxy's tests, but Opus 5.5 finished in 9.5 hours compared to Fable 5.1's 12 hours, and for 51% less cost. https://t.co/GJ9FaS3Erx

This post quotes another post: “Anthropic releases Claude Opus 5.5 model”