This has nothing to do with overloading. The suspicion is that when there is too much demand (or they just want to save costs), Anthropic sometimes uses a less capable (quantized, distilled, etc) version of the model. People want to measure this so there is concrete evidence instead of hunches and feelings.

To say that this measurement is bad because the server might just be overloaded completely misses the point. The point is to see if the model sometimes silently performs worse. If I get a response from "Opus", I want a response from Opus. Or at least want to be told that I'm getting slightly-dumber-Opus this hour because the server load is too much.