harness

Last week was all about the harness. Gone are the times when the models were all things-in-themselves. Now, as with early Homo erectus, the tools are the factor of survival. If we look at the types of harness-related posts and announcements, we will see three trends.

Harness products

Several companies have released either agents or infra for agents at once.

OpenAI has released the execution framework that their Codex (the CLI one) is based on. Unsurprisingly called Harness, it is their answer to the Claude Agent SDK and the GitHub Copilot SDK. The Harness provides the execution loop, memory, tools, and other necessities of agentic life. You can use it in three different ways. First, you can just use codex exec to run non-interactive jobs. Second, you can use the Codex SDK for building workflows. And last, you can use app-server to build apps that require conversation handling. One point worthy of attention is that they claim that the Harness improved the performance of the GPT-5.6 Sol model from 13.3% to 38.3% on ARC-AGI-3. It’s unclear what harness (not capitalized) was used as a baseline, though.