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Petri 2.0: New Scenarios, New Model Comparisons, and Improved Eval-Awareness Mitigations ​

Publication Date: January 22, 2026

Summary ​

The Anthropic Alignment Science team has released Petri 2.0, an updated version of their automated behavioral auditing framework for large language models. This release introduces improvements focused on countering evaluation-awareness, expanding the scenario library, and enhancing infrastructure.

Key Updates ​

Eval-Awareness Mitigations ​

The team identified that capable models can recognize when being tested and adjust behavior accordingly, potentially overestimating safety. Two complementary strategies address this:

Realism Classifier: A prompted system monitors auditor behavior to flag implausible or unrealistic actions. The approach distinguishes between task-driven cues (inherent to scenarios, measuring intended behaviors) and environment-driven cues (avoidable signals like implausible user actions).

Manual Seed Improvement: The team manually reviewed and revised seed instructions by adding concrete context, removing explicit oversight-lack language, and restructuring scenarios for greater plausibility.

Results showed both approaches reduced eval-awareness rates across tested models, with combined interventions producing "47.3% median relative drop in eval-awareness" on Claude models.

Expanded Seed Library ​

The update adds 70 new seed instructions covering additional behaviors including multi-agent collusion, professional-ethical conflicts, scenarios involving sensitive information, and interactions with unconstrained models.

Infrastructure Improvements ​

  • Compatibility with reasoning summaries from modern APIs
  • Routing to original model providers for open-weights models
  • Performance optimizations reducing CPU bottlenecks
  • Streamlined, modularized codebase

Evaluation Results ​

Testing across 10 target models using Claude Sonnet 4.5 and GPT-5.1 as auditors, with scoring from Claude Opus 4.5, Gemini 3 Pro, and GPT-5.1:

  • Claude Opus 4.5 and GPT-5.2 show strongest alignment results
  • Grok 4 exhibits elevated user deception rates
  • Gemini 3 Pro shows increased verbalized eval-awareness compared to predecessor
  • GPT models demonstrate lowest unprompted initiative rates

Resource ​

The latest Petri version is available at github.com/safety-research/petri. The team welcomes community contributions of new seed instructions.