Claude Opus 5.5 Matches Fable 5.1 on Most Work for 40% Less

Update, Sept. 28: Anthropic has since released Claude Sonnet 5.5, the second model in the family, at the same $2 and $10 per million token prices as Sonnet 5. Haiku 5.5 is still to come.

Anthropic’s newest Opus model performs about as well as its bigger Fable 5.1 on most work and costs 40% less to run than Opus 5, the company said Tuesday in announcing Claude Opus 5.5. It arrives two months after Opus 5 shipped on July 24.

Part of the savings is price. Input and output tokens now cost $4 and $20 per million, down from $5 and $25. Cache reads, which Anthropic says make up most of the cost of agentic and coding work, fall to $0.20 per million tokens from $0.50. The rest comes from efficiency, since the model uses fewer tokens per task and generates output more than 30% faster. A separate fast mode in Claude Code and on the Claude Platform runs up to 2.5 times quicker for $8 and $40 per million tokens.

Long jobs, fewer tokens

Anthropic pitched the model at sprawling work such as codebase migrations and audits. One early tester had it audit and fix a 200,000-line codebase in under three hours, a job that took Opus 5 more than 20 hours and 2.5 times as many tokens. In an internal test, Opus 5.5 and Fable 5.1 each translated the HAProxy load balancer from C into Rust. Both versions passed nearly all of HAProxy’s regression tests, but Opus 5.5 finished in 9.5 hours to Fable’s 12 and cost 51% less.

“I handed Claude Opus 5.5 a large engineering task across six of our repositories and let it run overnight, unattended,” said Sean Heintz, a staff software developer at Clio, as quoted by Help Net Security. “I’m struggling to find anything negative to say.” On Artificial Analysis’s GDPval-AA test of professional work across 44 occupations, Opus 5.5 scored 1846 Elo against 1735 for Fable 5.1, and at its default effort setting it beat OpenAI’s GPT-6 Astra at max effort for about a fifth of the cost per task.

The model also writes differently. It puts key information first, leans less on jargon and follows writing instructions more closely, TechCrunch noted. Thinking can no longer be switched off, though developers can set how much effort it applies.

Safeguards and availability

This is Anthropic’s first release since CEO Dario Amodei called for pacing capability gains so safety work can keep up. METR and Frontier Design tested the model before launch, and in a new containment test it tried to get around its limits about 85% less often than Opus 5 or Claude Mythos 5.1. Because its biology and cybersecurity skills are comparable to Mythos 5.1, it ships with Fable-level safeguards, and vetted researchers can apply for wider access.

Opus 5.5 is available through the Claude API as claude-opus-5-5 and on AWS, Google Cloud and Microsoft Azure. Anthropic also raised five-hour usage limits on Pro, Max, Team and seat-based Enterprise plans.