# Evidence-sufficiency judgment

On evidence-sufficiency judgment, a domain with no decidable correctness reward, a boundary-keeping recipe of supervised fine-tuning followed by GRPO on an LLM-judge reward raised spontaneous correct refusal under action pressure from 25% in the instruction-tuned baseline to 100% (40 per arm; Wilson 95% CI lower bound 91.2%, non-overlapping with the baseline interval [14.2%, 40.2%]), while a scrambled-pairing placebo fell to 5%. The same recipe's automatic false refusal on 281 well-formed claims was 1.1% (Wilson upper bound 3.09%), so the effect is boundary-specific rather than blanket refusal; SFT saturates the face, leaving the GRPO increment not separately identifiable, and ratings come from model sessions, not human experts.

On evidence-sufficiency judgment, a domain with no decidable correctness reward, a boundary-keeping recipe of supervised fine-tuning followed by GRPO on an LLM-judge reward raised spontaneous correct refusal under action pressure from 25% in the instruction-tuned baseline to 100% (40 per arm; Wilson 95% CI lower bound 91.2%, non-overlapping with the baseline interval [14.2%, 40.2%]), while a scrambled-pairing placebo fell to 5%. The same recipe's automatic false refusal on 281 well-formed claims was 1.1% (Wilson upper bound 3.09%), so the effect is boundary-specific rather than blanket refusal; SFT saturates the face, leaving the GRPO increment not separately identifiable, and ratings come from model sessions, not human experts.