TLDR: Agent = Model + Harness. Harness engineering is how we build systems around models to turn them into work engines. The model contains the intelligence and the harness makes that intelligence useful. We define what a harness is and derive the core components today's and tomorrow's agents need.
A harness is every piece of code, configuration, and execution logic that isn't the model itself. A raw model is not an agent. But it becomes one when a harness gives it things like state, tool execution, feedback loops, and enforceable constraints.
There are things we want an agent to do that a model cannot do out of the box. This is where a harness comes in.Models (mostly) take in data like text, images, audio, video and they output text. That's it. Out of the box they cannot:
- Maintain durable state across interactions
- Execute code
- Access realtime knowledge
- Setup environments and install packages to complete work
These are all harness level features.