Everyone is making an agent harness, you should build another one (for yourself)

Thu, 29 Oct 2026 02:30:00 +0700

The first project I shipped after Claude Opus 4.5 came out was my own agent harness.

Opus 4.5 came out on 2025-11-24. For many developers, me included, it was the point where coding agents started to work for real. Ethan Mollick had early access and posted this on launch day:

I had early access to Opus 4.5 & it is a very impressive model that seem to be right at the frontier Big gains in ability to do practical work (like make a PowerPoint from an Excel) and the best results ever (& in one shot) in my Lem poetry test, plus good results in Claude Code
— Ethan Mollick (@emollick) November 24, 2025

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Everyone is making an agent harness, you should build another one (for yourself)