DeepSeek Harness Arrives, and It Doesn't Aim to Be the Next Codex

DeepSeek has launched its first Agent product, Harness, which is not a Codex-style offering but rather a "recomposable, replayable Agent runtime." Its core principle is "everything is a plugin," where "Agent presets" determine tools and capabilities, allowing models, interfaces, and more to be interchangeably combined. It treats Agents as infrastructure, enabling users to assemble their own bespoke Agents rather than merely using a general-purpose product.