What a mystery, will Cursor never reply to this? But actually it seems it’s no longer a mystery. In the current beta of 0.47 it’s suggested (with even a screenshot in the docs) they renamed it to Auto-select model. Though whenever it’s Claude Sonnet 3.7 thinking, it means “default” was “improved” (their words) to cost 2 requests instead of 1!
@haojixing, please consider marking my reply as Solved.