Comment by eudoxus

I think some of the distinction here is that the more recent "bare LLMs" have been more purpose built, augmented with "agent" specific RL, and in general more fine tuned for the requirements of "agents". Things such as specific reasoning capabilities, tool calling, etc.

These all make the "bare LLMs" better suited to be used within the "agent" harness.

I think the more accurate term would be "agentic LLMs" instead of calling them "agents" outright. As to why its the case now, probably just human laziness and colloquialisms.