Anthropic's new flagship claims Fable 5.1-level performance at a fraction of the cost—but GPT-6 Astra still beats it on two published benchmarks.
Anthropic says Claude Opus 5.5 rivals Fable 5.1 on most work at 40 percent lower cost than Opus 5, with tougher safeguards.
Anthropic called it "the strongest-performing model we've tested to date."
