Anthropic launches Claude Opus 5.5 at 40% below Opus 5
Anthropic released Claude Opus 5.5 on September 22, 2026, the first model in its Claude 5.5 family. Anthropic says it performs at the level of Claude Fable 5.1 on most work and generates output more than 30% faster than Opus 5. Pricing drops to $4 per million input tokens and $20 output, from $5 and $25, and cache reads fall from $0.50 to $0.20. It reports 66.4% on Terminal-Bench 4.0 and 81.8% on OSWorld 2.1. Thinking can no longer be turned off, and biology and security tasks route to Opus 4.8 unless the account is in a verification program.
Why it matters
It now leads the Artificial Analysis Intelligence Index at 58, ahead of Fable 5.1 and GPT-6 Astra at 53, while costing less than either. The top model is no longer the most expensive one.
Who should care
Anyone on Opus 5 or Fable 5.1, and teams choosing a default model for agents
What you can do
Read the four breaking changes in the migration guide before switching, then rerun your evals on claude-opus-5-5. If Fable 5.1 was only there for quality, compare the two on your own tasks.