The “For You” feed has always been X’s way of deciding what you see, not yours. But X custom timelines are changing that, at least for paying subscribers. X has officially launched Custom Timelines, a new feature that lets Premium subscribers pin a specific topic directly to their home tab. The feed then builds itself around that subject using Grok, X’s AI, combined with the platform’s existing personalization signals. It works best for topics you already interact with, according to X Head of Product Nikita Bier. At launch, there are more than 75 topics to choose from, covering everything from art and sports to finance. iOS Premium subscribers are getting early access first, with Android support coming later. Bier also announced a second tool launching alongside it: a topic snooze option for the For You tab. If a subject is flooding your feed and you want to dial it back without blocking anyone, you can now mute it temporarily. That one is rolling out to Premium users on both iOS and web.…