The task of building an agent harness is to create a software layer that enhances a model’s runtime execution through context management, tool invocations, loop control, orchestration, and error handling. Building applications on top of rapidly improving models is, however, a modern engineering challenge. How can we design software today that absorbs the performance gains from future model releases?

This requires forecasting how models will evolve, staying optimistic about their progress, limiting assumptions, and avoiding hand-crafted optimizations.

We learned this the hard way seven months ago, when we had to abandon our first attempt at deep research and rebuild the entire system from scratch. The first architecture was complicated and sophisticated (we thought this was a good thing), but its assumptions became bottlenecks when the next generation of models arrived.

Over the last seven months, model capabilities have quietly but meaningfully evolved (especially in their tool-calling abilities). This single optimization focus has pushed us from workflows to agents. We believe future models will be trained to solve the current pain points of agent developers. Every model is ultimately consumed by a harness, so models should evolve in service of that harness. We hope to see models improve in high-recall summarization (for context compression), tool-calling reliability, and concision in writing.

Similarly, tools should evolve to support LLMs and widely adopted agent harnesses. The best tools should perform some context engineering on the tool side, abstracted away from the agent. They should return only the most relevant data instead of dumping large volumes of tokens into the context window.

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