GQuuuuuuX is director Kazuya Tsurumaki's (FLCL, Diebuster) pet project: from interviews it seems like all the impetus for this collaboration between Studio Khara and Sunrise can be attributed to him.
However, this episode? The lovingly rendered shot-for-shot recreation of the the first episode of the original 0079 Gundam (minus some alt timeline shenanigans), complete with remixed versions of the original bgm and sound effects? This is all Anno, and probably the closest we'll get to a Shin Gundam.
Anno's major contribution to this project has been on the scripts, with him fleshing out this alternate timeline while Youji Enokido (Revolutionary Girl Utena) wrote the "modern" segments of the story. To say that the staff list for this is kinda cracked would be an understatement.
The theatrical release had the movie start with the footage from this episode, along with another 15 mins or so of extra footage that paced things better. It's a bit disappointing that we couldn't get an extra long episode to get the entire prologue, although I get the feeling that we'll see the events that were cut for time here later on in the show as a flashback. (Also, going from this Gundam Origins artstyle to the rest of the show's hyper-stylized Pokemon-esque designs did induce some whiplash)
(Challia Bull was a "villain of the week" who was easily dispatched in the original show, in episode 39 to be exact- now in 2025 he's experienced twink rebirth via Yaoi fanshippers. What a time to be a Gundam fan, this is the best kind of "fanservice"- Gundam would have died stillborn if not for Yaoi fanshippers keeping interest in the show alive until Sunrise sorted out their merchandising funded model. Thank you Anno for giving the people what they want)
Edit: Also we finally got the opening, and it has a bunch of callback's to Zeta Gundam lmao
This episode was literally a 0079 episode but with better animations/art. Everything else was the same as the original.
Well, not quite everything