same open model, different harness => very different results
Joël set out to find which harness actually gets the most out of open models in November 2026
Joël Niklaus releases a Harness Leaderboard comparing nine coding-agent harnesses on open models
AIJoël Niklaus releases the Harness Leaderboard, which compares nine coding-agent harnesses with the model, provider and reasoning effort held fixed. Across 28,849 trials on Terminal-Bench 2.1 and DeepSWE, averaged over three open models, mini-swe-agent solves 51.4% of tasks and OpenClaw 27.3%.
AIWhy it matters.
The leaderboard holds the model fixed and varies only the harness, showing how much the agent wrapper alone changes solve rates and cost per task.
Thomas WolfVerified on X
@Thom_Wolf
I burned a shitload of compute so you don't have to. Releasing the Harness Leaderboard. Which harness should you run your open model in? I ran 28,849 trials to find out. The leaderboard compares nine coding-agent harnesses on open models. In each comparison only the harness changes: the model, provider and reasoning effort stay fixed, and every task gets three attempts. The trials ran GLM-5.3-Flash, DeepSeek-V4.1-Flash and Flint on Terminal-Bench 2.1 and DeepSWE, for $4,746 of inference. Averaged over the three models, mini-swe-agent (@KLieret), a bash-only agent, solves 51.4% of tasks and @openclaw 27.3%. Four others are statistically tied with mini-swe-agent. One of them is Pi (@pidotdev), at 49.4% for $0.29 per solved task, about 45% less than mini-swe-agent's $0.53. The best harness depends on the model: mini-swe-agent on GLM-5.3-Flash, Hermes Agent (@NousResearch) on DeepSeek-V4.1-Flash and Kimi Code (@Kimi_Moonshot) on Flint. @opencode costs $3.35 per solved task, 11.7 times as much as Pi. See Harness Hub's Harness Lens for what the nine harnesses do differently. It documents the prompts, tools and compaction of 34 coding-agent harnesses and links every claim to its source. Leaderboard: https://huggingface.co/spaces/joelniklaus/harness-leaderboard Harness Lens: https://huggingface.co/spaces/harness-hub/harness-lens
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Thomas Wolf · x.comPublished · added here
Original title: same open model, different harness => very different results