Per Anthropic, Claude Opus 5.5 performs at the level of Fable 5.1 on most work and costs 40% less than Opus 5 on typical work

The most useful line around this release is not from Anthropic. It is from Vercel's note, and it says some requests will start returning a 400 error.

Opus 5.5 does not accept a fixed thinking budget and does not let you force the model to call a specific tool. If your system has been getting JSON back by forcing a tool call, it will stop working when you switch models. You rewrite it with structured outputs and run it again.

Where the saving is

Part of the discount is in the token price. Anthropic looks for the rest in the model reaching the result with fewer tokens. The example they give comes from an early tester: an audit and fix of a 200,000-line codebase in under three hours, where Opus 5 worked for over 20 hours and spent 2.5 times as many tokens.

That is their number from an early tester, not ours. But it is the number easiest to check at home: same task, same repository, both models, and the bill at the end.

A cheap token is an advert. A cheap task is a result.

There is also one sentence worth reading. Anthropic writes that it sees signs the model often suspects it is being tested, and that this makes it harder to judge how it will behave out in the world. Good that they say it themselves.

If you use Opus through the API, check your code for forced tool choice and a fixed thinking budget before you change the model name.

The visual is generated code-art, no third-party images.