Microsoft Research and Microsoft Red Team describe Lazarus, a technique that rewrites fewer than 10 dormant neurons in an open-weight model's final feed-forward layer so it emits attacker commands when a trigger appears, such as a date change. No retraining is required, and an agent using the modified model can run those commands with whatever permissions it holds. Microsoft Threat Intelligence said it has not seen threat actors use the method, but the researchers urge teams to verify the integrity of model weights, including internally developed models.

Anthropic released Fable 5.2 and Mythos 5.2, which share one underlying model with different safeguards. Fable is broadly available, while Mythos is limited to vetted cybersecurity and life sciences organizations; both cost $8 per million input tokens and $40 per million output tokens, down from $10 and $50. Anthropic reports Fable 5.2 scored 49.1% on the FrontierCode 2.0 benchmark, up from 32.4% for Fable 5.1, and that output generation is up to 30% faster.