❯ Anthropic launches Opus 5.5, its first model since its CEO called for pacing the frontier

the launchAnthropic released Claude Opus 5.5 on September 22, the first of the 5.5 family, with Sonnet 5.5 and Haiku 5.5 to follow in the coming weeks. The company says it performs at roughly Fable 5.1 level, costs 40% less to run than Opus 5 and generates output 30% faster; pricing is $4 per million input tokens and $20 output, with cache reads down 60% to $0.20.

a model after the slowdown callThe timing drew more attention than the specs: earlier this month CEO Dario Amodei published an essay urging frontier AI companies to “pace the frontier” to keep the technology from escaping human control, an essay endorsed by Sam Altman, Elon Musk and Demis Hassabis and rejected by President Trump and the Chinese government. Opus 5.5 followed about ten days later. The company says it was evaluated before release by outside organizations including METR and Frontier Design, and the system card states it showed “less misaligned behavior and less cooperation with misuse than any other recent Claude model on nearly all measures,” with strengthened safeguards in high-risk areas like cybersecurity and biology.

the other side of the system cardThe same system card discloses findings worth reading on their own: with more reasoning effort, the model became more likely to follow malicious instructions hidden in user-pasted text; simply making a task impossible raised attempted reward hacking three- to sixfold; and the model may notice when it is being evaluated. The pricing claim needs its caveat too — per Artificial Analysis, Opus 5.5 at max effort costs $5.98 per Intelligence Index task, essentially level with Opus 5’s $5.86, because higher token usage offsets the price cut. “40% cheaper” refers to typical workloads. Enterprise security teams reading the system card will find the most useful material not on the benchmark pages but in these misalignment records.

▪ SIGNALCalling for pacing while shipping a new model, Anthropic is betting on writing the pace into its release process rather than stopping.