I am fairly certain there is a backend priority for tasks, the 'batch' that runs at lower usage times. Does it need to be done 'now' or can it wait? I would assume there is a shifted priority queue for those on subscription and based upon a urgency defined by the bot (and maybe the user).

Without having access to the logs because Grok Bot does not expose much of the workings I am going to assume they are capturing bot requests, batching them, and finding the path to least API user impact. Without model selection my guess is there are a lot of model routing.