Players who choose the Mountain Pass route near the tail end of the first act of Baldur's Gate 3, will eventually find a Githyanki crèche, where the party can follow a lead on how to remove the Illithid parasite swimming in their brains. The process involves a Zaith'isk, a suspicious device that's supposedly designed for tadpole extraction.
Baldur's Gate 3: Should You Let Lae'Zel Enter the Zaith'Isk
There's a lot more going on with the Gith Zaith'Isk in Baldur's Gate 3, and choosing who to put in it might make or break a campaign.