HarnessPro is a label-free framework for recursively improving an AI agent’s harness: the instructions, tools and runtime policies that shape how it works. It evaluates candidate changes with synthesized tests and retains configurations across different performance–cost trade-offs, rather than treating one setup as best for every use case.
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What an agent harness does
A harness is the surrounding setup that guides an agent’s work—not just the underlying model. It can include instructions, available tools and runtime policies. HarnessPro’s premise is that changing this setup can affect both task performance and execution cost.
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How HarnessPro improves a harness
HarnessPro uses execution traces to identify patterns in failures and costs, then generates candidate changes to the harness. Those candidates are evaluated with synthesized tests instead of relying on ground-truth solutions or official tests during optimization, according to the project README.
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The process is recursive: candidate harnesses can be evaluated and refined in further rounds. That makes HarnessPro a method for evolving the agent’s operating setup, rather than a change to the model’s weights.
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Why it keeps Lite, Medium and Heavy options
A cheaper harness may be preferable when cost matters most; a more capable one may be worth choosing when performance is the priority. HarnessPro’s Pareto-based selection preserves three operating points: Lite for lower cost, Medium for balance and Heavy for higher performance.
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The practical idea is to make the trade-off explicit. Teams can select among the available options according to their deployment needs instead of assuming that the configuration with the highest score is always the right choice.
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What the reported benchmarks show
A project results page reports that, with GPT-5.5 and Codex on Terminal-Bench 2, HarnessPro Heavy achieved an 80.8% pass rate at $0.72 per task. The same comparison lists RHO at 76.3% and $1.09 per task.
16 Separately, research summaries report an average pass-rate gain of 2.0 percentage points and a 26.1% reduction in per-task cost versus RHO for the reported evaluation setup.
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These figures describe particular model, harness and benchmark combinations. They should not be read as evidence that HarnessPro will produce the same gains on every task or deployment. The project presents multiple variants precisely because performance and cost can pull in different directions.
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