The Claude Opus 4.5 system card [0] is much more revealing than the marketing blog post. It's a 150 page PDF, with all sorts of info, not just the usual benchmarks.

There's a big section on deception. One example is Opus is fed news about Anthropic's safety team being disbanded but then hides that info from the user.

The risks are a bit scary, especially around CBRNs. Opus is still only ASL-3 (systems that substantially increase the risk of catastrophic misuse) and not quite at ASL-4 (uplifting a second-tier state-level bioweapons programme to the sophistication and success of a first-tier one), so I think we're fine...

I've never written a blog post about a model release before but decided to this time [1]. The system card has quite a few surprises, so I've highlighted some bits that stood out to me (and Claude, ChatGPT and Gemini).

[0] https://www.anthropic.com/claude-opus-4-5-system-card

[1] https://dave.engineer/blog/2025/11/claude-opus-4.5-system-ca...