I'm building a product on the Claude Agent SDK, and it is the best in a specific way.

Codex and Open Code are competition for coding, but if we talk about an open-ended agentic harness for doing useful work... well it was bad enough a year ago I'd consider anyone even claiming one exists to be a grifter and now we have one.

And while being first might not matter, I think having both post-training and the harness being developed under the same roof is going to be hard to beat.