harnesses

These results show that a model’s capabilities are compatible, generalizable and can carry over to other harnesses. Providers do report to optimize some models for their own coding environments: OpenAI, for example, describes GPT-5-Codex as optimized for agentic software engineering in Codex.12 Yet we observe that a shared provider does not guarantee the best pairing. The practical question remains which harness delivers the best balance of cost and task success for a given model and workload.

One threat we’re particularly focused on is prompt injection, and we handle it in layers. The model is trained to recognize and resist it. The harness marks anything coming from an untrusted source. Deterministic code checks the result. And an ensemble of classifiers runs where the agent can't reach them.

the Unix / Linux Environment is a natural candidate, and could be turned into an Agentic harness with a few modifications.

Every SaaS business will become a harness around a model, whether or not they’ve realized it yet.

Harrison’s 4 elements of an agent remain – the system prompt, planning tool, file system, and subgents – describing the core loop. This is the core loop the developer controls with the keyboard. The harness manages everything beyond this, the world the developer sits within.

If this continues, there’s a world where 3rd party harnesses become less valuable when used with frontier lab models because the 1st party harness behavior is already baked in. And there’s no longer a fine tuning escape hatch to generalize this behavior away.

I get pushback that falling inference prices will eventually bring us back to sending everything through the largest models. But I’m not so sure: those same gains will benefit the K3s and Qwens, and as we continue to develop better harnesses it will be easier to provide weaker (but still great) models with sufficient context to perform well.

It’s going to be funny if the network effects the AI labs have been searching for end up looking just like the network effects of the SaaS era. Coding harnesses, managing the environments around the agent, look a whole lot like the SaaS platforms of old.