Stanford Meta-Harness Autonomously Improves Its Own Harness, Significantly Beats Claude Code on TerminalBench 2

r/singularity / Stanford IRIS Lab·high signal

Stanford researchers published Meta-Harness, a system that evolves its full coding harness (system prompts, tool definitions, completion-checking logic) by reading per-task execution traces — up to 10M tokens of diagnostic context per optimization step. On Opus 4.6, Meta-Harness achieves 76.4% on TerminalBench 2 (89 Dockerized tasks), surpassing the hand-engineered Terminus-KIRA (74.7%). On Haiku 4.5, it hits 37.6%, beating the next-best agent Goose (35.5%). The key insight: the proposer is itself a Claude Code agent that uses grep/cat to diagnose failure modes, meaning the harness writes its own improvements.