Opus 5.5 sends most cybersecurity work to the older Opus 4.8, and does it without refusing, so you may not notice

September 22. Opus 5.5 is the first Opus model to ship with the same kind of safeguards as Claude Fable 5.1 for cybersecurity, biology and distillation. Anthropic's launch page says finding and fixing bugs in your own code as part of normal development stays on Opus 5.5, 'but most cybersecurity tasks will be re-routed to Opus 4.8.' The fallback is transparent, meaning you get an answer from the older model instead of a refusal. Biology work falls back the same way. Distillation attempts are blocked outright with no fallback. The way out is Anthropic's Cyber Verification Program, which will add Opus 5.5 in the coming weeks with three tiers of access, and a new Life Sciences Verification Program for labs and drug companies. Why it matters: an MSP or security team that benchmarks Opus 5.5 on pentest or triage work may be benchmarking Opus 4.8 without knowing it.