> What does it matter which tool I use when I hit the limit?

A third party harness may have a misconfiguration of prompt caching, leading to more load on Anthropic's servers, they could also have wildly different usage patterns (Hermes, openclaw etc), also making it hard to predict the load. If you constrain everyone to use your own harness, at least you're in control of that.

The first point is sort of funny though, because their own harness had a misconfigured prompt caching for several months during the times where they were crying about third party harnesses (/resume was busting cache all the time).