Claude Opus 5.5

Model id claude-opus-5-5, released 2026-09-22 as 'the first model in our new Claude 5.5 family'. Anthropic says it 'performs at the level of Claude Fable 5.1 on most work and costs 40% less to run than Opus 5'. Priced at $4/$20 per MTok (20% below Opus 5), with cache reads at $0.20 (60% less than Opus 5). It has a 1M context, 128K max output, adaptive thinking that is always on (it can't be disabled), and medium default effort. It ships with Fable-5.1-class cyber/bio safeguards, and flagged cyber tasks fall back to Opus 4.8. Launch scores were run with safeguards on, which Anthropic says likely depresses some rows.