Anthropic released Claude Opus 5.5 for coding agents and knowledge work, outperforming Mythos 5.1 and Fable 5.1 at $4/$20 per million input/output tokens—20% below Opus 5, with typical workloads 40% cheaper. Cache-write is $5 and cache-read $0.20 per million tokens. It leads Anthropic models on agen