Yep Kilo (and Cline/Roo more recently) push these free trial of the week models really hard, partially as incentive to register an account with their cloud offering. I began using Cline and Roo before "cloud" features were even a thing and still haven't bothered to register, but I do play with the free Kilo models when I see them since I'm already signed in (they got me with some kind of register and spend $5 to get $X model credits deal) and hey, it's free (I really don't care about my random personal projects being used for training).

If xAI in particular is in the mood to light cash on fire promoting their new model, you'll see it everywhere during the promo period, so not surprised that heavily boosts xAI stats. The mystery codename models of the week are a bit easier to miss.