We’re introducing Claude Opus 5.5, the first model in our new Claude 5.5 family. It performs at the level of Claude Fable 5.1 on most work and costs 40% less to run than Opus 5. Claude Opus 5.5 is our first release since we called for pacing the frontier. It was tested before release by external evaluators, including Frontier Design and MET R. On our automated behavioral audit, the most comprehensive alignment test we run, Opus 5.5 is the strongest-performing model we’ve tested to date. It also comes with the safeguards we’ve developed for our most capable models.

Opus 5.5 is a major step up from Opus 5. One tester completed a 680,000-line code migration in less than a day—work that would have taken an engineering team weeks. When asked to cut load times across every page of a web app, Opus 5.5 succeeded 39 of 40 times, while Opus 5 made smaller improvements that also altered the app’s behavior. A different tester had several Claude models build a game from a single prompt; Opus 5.5 scored higher than any other model on graphics and polish.

Opus 5.5 achieves the best scores of any model to date on our automated behavioral audit. It is much less likely than recent models to take hard-to-reverse actions or act outside the boundaries it’s been given, and it’s more resistant than Opus 5 to prompt injection. It is comparable to Claude Mythos 5.1 in biology and cybersecurity, so we’re deploying it with safeguards similar to those on Claude Fable 5.1. Vetted organizations can apply today to our Life Sciences Verification Program to use Opus 5.5 for biology research.

Opus 5.5 requires less compute to serve than Opus 5, with input and output tokens at $4 and $20 per million—20% less than Opus 5. Cache reads are $0.20 per million tokens, 60% less than Opus 5. Opus 5.5 also generates output more than 30% faster than Opus 5. We’re increasing five-hour usage limits on Pro, Max, Team, and seat-based Enterprise plans. Claude Sonnet 5.5 and Claude Haiku 5.5 will follow in the coming weeks.