The article documents a failure class in frontier large language models called exception chain collapse, where models incorrectly evaluate nested conditional rules. To address this, the authors present the Aethis Eligibility Module, a neuro-symbolic architecture that combines LLM-authored rules with an SMT-based layer for deterministic execution.

  • The system ensures consistent rule execution regardless of model drift or prompt format changes.
  • In a 20-scenario adversarial test on construction insurance, the engine scored 20/20, matching only one of four frontier configurations.
  • External validation on LegalBench tasks showed the engine was significantly more accurate than three frontier models, with margins up to +41 points against Anthropic models.

The contribution relocates uncertainty from the inference boundary to the specification boundary, making it deliberate and audited for regulated workflows.