Claude Opus 5.5
Anthropic is introducing Claude Opus 5.5, the first model in its 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. It is Anthropic's first release since the company called for pacing the frontier, and it was tested before release by external evaluators including Frontier Design and METR. On Anthropic's automated behavioral audit, its most comprehensive alignment test, Opus 5.5 is the strongest-performing model tested to date, and it comes with the safeguards developed for Anthropic's most capable models.
On performance, Opus 5.5 is a major step up from Opus 5 and is the new leading model, with early testers seeing large jumps on their most complex work. One tester completed a 680,000-line code migration in less than a day—work that would have taken an engineering team weeks. It is also good at finding and fixing software inefficiencies: 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. Another tester had several Claude models build a game from a single prompt; Opus 5.5 scored higher than any other model on the strength of its graphics and polish.
On safety, Opus 5.5 achieves the best scores of any model to date on Anthropic's automated behavioral audit, the alignment suite that tests Claude across thousands of simulated scenarios. It is much less likely than recent models to take hard-to-reverse actions or act outside the boundaries it has been given, and it is more resistant than Opus 5 to prompt injection. Anthropic has also broadened its alignment testing to cover longer tasks, impossible tasks, and scenarios modeled on real incidents, though it says the model still has limits. Full evaluation details are available in the Opus 5.5 System Card.
Because Opus 5.5 is comparable to Claude Mythos 5.1 in biology and cybersecurity, Anthropic is deploying it with safeguards similar to those on Claude Fable 5.1. Vetted organizations can apply today to its Life Sciences Verification Program to use Opus 5.5 for biology research. In the coming weeks, Anthropic will also expand access to its Cyber Verification Program, and verified cybersecurity practitioners will be able to use Opus 5.5 for their work.
On cost and speed, Opus 5.5 requires less compute to serve than Opus 5, and its pricing reflects that. Anthropic's tests show that at default settings it will cost 40% less than Opus 5 on typical workloads. Input and output tokens are $4 and $20 per million, 20% less than Opus 5. Cache reads—which make up the majority of agentic and coding work costs—are $0.20 per million tokens, 60% less than Opus 5. Opus 5.5 also generates output more than 30% faster than Opus 5.
In addition to the price drop, Anthropic is increasing five-hour usage limits on Pro, Max, Team, and seat-based Enterprise plans. It is also providing subscription users a rate limit reset, though the excerpt is cut off at that point.