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Harness²

GitHub stars: 17.6K GitHub forks: 1.6K Declared license: Apache-2.0: Apache-2.0 Last pushed October 14, 2026: Pushed 8d ago
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Harness² is a Google Research framework for experimenting with the system around an AI model: its prompts, tools, memory, skills and orchestration. It refines that harness while keeping model weights fixed.

The repository includes a local demo, benchmark adapters and saved experiment outputs. It is research code, and the README says it is not an officially supported Google product. Use this as a first read, not a recommendation. Open the original project before trusting details like terms, limits, privacy, cost, setup, or safety.

What it is

Experiments around a fixed model

A task-level loop proposes harness changes, probes them on the same task and composes a refined harness from differences between executions. This refinement does not use ground-truth feedback.

Why it stands out

Refinement within and across tasks

After adopting a harness, a second loop saves it and evidence-supported lessons for later tasks in the same domain. Task-level refinement and the persistent improvement library therefore work at different timescales.

Availability

Source, demo and benchmark runners

The public repository provides Python code, tests and setup guides. The project declares Apache-2.0; see the repository and each upstream benchmark for current terms.

Why it matters

What makes it useful

Agent behavior depends on more than the model checkpoint. Harness² exposes editable components including prompts, tool guidance, memory and skills, making those parts available for experiments. Its local demo runs the recursion and library workflow with deterministic editors and real Python execution, without model credentials. That gives a builder a smaller way to examine the workflow before configuring model-backed benchmarks.

Notable points

What stands out

Parallel recursion probes a pool of candidate harnesses and uses their execution evidence in compositions. Sequential recursion carries a refined harness and its accumulated evidence through successive steps. Both save task artifacts, adopted harnesses and reflection notes. Failed evaluations remain unscored, so a missing judgment is different from a measured zero.

Before using

What to review

The setup guide recommends Linux and Python 3.12; package metadata also supports Python 3.13. Model-backed runs need additional runtimes, benchmark dependencies and model access. They incur API costs; the experiment guide recommends a small task selection first.

The repository says executor network access is unrestricted and Codex runs with its sandbox disabled. Its evaluation guide recommends network-level restrictions to reduce access to public benchmark answers and grading criteria. Review the documented execution access before running experiments.

Keep benchmark, executor, subset, recursion budget, mode and seed aligned across refinement, judging and reporting. The seed controls task ordering, not model sampling. Setup checks do not establish that every configured model is available.

Reader fit

Who may find it relevant

Agent researchers and developers comparing harness designs are the clearest audience. The credential-free demo offers an entry point for understanding the mechanism. Running the model-backed studies calls for comfort with command-line setup, model credentials and benchmark-specific dependencies.

Editorial note

Why LifeHubber lists it

LifeHubber lists Harness² because its proposed improvements leave concrete material to examine: the adopted agent setup alongside execution artifacts and reflection notes. For a builder investigating how a harness changed its approach to a task, those records connect the chosen instructions and tools with the work produced. They provide a basis for reviewing a proposed design change, while judging the quality of that change still needs a separate evaluation.

Source links

Source materials

Reader note

Before relying on this entry

LifeHubber lists entries to help readers inspect AI projects, not to endorse them or prove they are safe, suitable, accurate, maintained, or right for a specific use. We do not verify every entry in depth. Before relying on anything listed, review the original materials, terms, privacy practices, limits, and risks that matter for your situation.

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