Unless this was changed post-2e, the deal between Gith and Tiamat was after the liberation from the Grand Design and the schism between Githyanki and Githzerai. The Githzerai rebelled against Gith for going down the same path of tyranny they had suffered under the yoke of the Illithid Empire. Gith wanted to conquer the planes, the Githzerai and their spiritual leader Zerthimon demanded peace. For the deal with Tiamat, a group of Githyanki, led by Gith and including her advisor Vlaakith, travelled to Tiamat's domain in Avernus and Gith never returned, making Vlaakith I. the first queen of the Githyanki by her last decree - according to Vlaakith. The 2e-stats for Vlaakith CLVII. who we see in BG3, show a very powerful high-level githyanki lich, but except for being able to use a Githyanki's own plane shift ability to yank them back to Tu'narath, no special powers beyond that. Maybe those were lost in undeath. From what I remember, sources like the Illithiad or Guide to Astral Space only hint at Gith leading the first mind flayer thralls that became resistant to psionics, without particular bloodlines or details being mentioned. There are also no stats for "noble" Githyanki, but it's quite likely that Vlaakith would have consumed them all by now, since that hard level-cap and the ascension go back to at least 2e. The only other possibly noble Gith in the game is the Githzerai's spiritual leader Zaerith, who is said to have powers beyond imagination with rumours abound of him being half-illithid, undead or a god.
