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Why capability isn’t what limits long-running agents

Frontier models have capability to spare. What long, regulated work lacks is fidelity to the rules a model knows, held over time.

Nenya: The Durability Frontier: Why the Synthetic Workforce Depends on Black-Box Belief-State Control, Lossless Compaction, and Predicate-Conditioned Enforcement: A Frontier Step Beyond the Harness

Lindell S. Cumes

A biological protocol can run for weeks: cell lines to keep, assays to stage, a plan that changes as results come in, and rules on sterility, dosage and sequence at every step. A model that is right 97% of the time is not good enough when the other 3% is a contaminated cell line.

This synthesis of our June research argues that frontier models have capability to spare. What is scarce is fidelity, meaning actions follow the rules a model knows, and durability, meaning that fidelity lasts across millions of turns. Grant compliance, underwriting and legal research have the same shape.

What we found

  1. Fidelity belongs to the whole system. Improving one part at a time leaves the gap open.
  2. Three failures the literature reports separately turn out to be one problem: drift when the context is compacted, the gap between what a model believes and what it does, and the wall capable models hit.
  3. On a regulated task, fidelity rose from 0.43 for a plain agent to 1.00 with Nenya.
  4. With Nenya, a regulatory rule broken once stays learned. A bare model makes the same breach every time the situation comes back.
  5. In the paper’s model, the horizon over which an agent stays reliable grows exponentially with compute.
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