ResearchResearch paperReinforcement Learning · Robotics & Embodied AI1 source · Oct 17, 2026

When Better Policies Leave Harder Failures: Coverage Shift in VLM Success Monitoring

Can a better robot policy become harder to monitor?

Key points

  • We study a fixed vision-language model (VLM) that judges success while a policy improves.
  • In a controlled 20-seed tray-placement experiment, training selects only simulator-verified successes.
  • We call this change in conditional monitoring sensitivity coverage shift: learning changes which failures reach a fixed judge.
  • Judge-filtered experiments across eight settings further show heterogeneous effects of state-dependent acceptance.

Sources (1)

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