Anthropic released Opus 4.8 on May 28, and the formal-methods jump is showing up everywhere.

Beyond the Zcash audit, it one-shot a formally verified polygon-intersection proof earlier models failed (GitHub) and is anchoring agentic Lean 4 theorem-proving frameworks (arXiv). The pattern across these is deep-correctness, machine-checkable work, exactly the domain where you'd least expect a sudden leap. If your last impression of frontier-model formal reasoning is from a few months ago, it's stale.