Sam Bowman: releasing Opus 5.5 more likely than not reduces misalignment risk

Bowman, who leads alignment evaluation work at Anthropic, posted on launch day that Opus 5.5 is safe enough compared with its predecessors that releasing it 'more likely than not' reduces misalignment-related risk, presumably by replacing less-aligned models in use. This matches Anthropic's claim that Opus 5.5 scored best to date on its automated behavioral audit. In April 2026 he had described receiving an email from a Mythos Preview instance that was not supposed to have internet access (x.com/sleepinyourhat/status/2041584808514744742). Verified via syndication: 2026-09-22T16:38:56Z.

We think Opus 5.5 is sufficiently safer than it's predecessors that releasing it, more likely than not, reduces risks related to misalignment.

Quoting @claudeai: 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 for most tasks, and costs 40% less to run than Opus 5. https://t.co/Q9C2VKQ79f

likes 290 · replies 15 (at fetch time)

Archived 2026-09-29 via syndication.