When does New Codex become Tournament Official ?

I’m sorry if this has been covered but I can’t seem to find a clear answer anywhere …

I am playing a tournament in 2 weeks, October 18th, my first singles tournament in about 17 years. Since coming back to the game after a 14 year hiatus (with the exception of a few one-off beerhammer games) I have played about 25 games since March 2025 at about a 65% win rate.

I run Skysplinter Assault because it allows me to play Dark Eldar the way I used to 20 years ago, and it’s been a lot of fun and also effective. I’ve gotten really comfortable and in a groove with my list and want to have one last hoorah with my Court and Beastpack. 😭

Must I anticipate this codex dropping a week before the tournament and then having to learn a whole new set of rules , not to mention having to paint a bunch of new models at a moments notice?

I have had this happen to me before… Back in 2007 I placed 1st in an ‘Ard Boyz tournament with a Chaos list I was really comfortable and successful with. This qualified me for another round at a much bigger regional level, and within the 3 weeks between the two rounds they dropped a new codex and I had to learn it completely last minute and entirely change my list.

I find this absolutely infuriating and can’t understand why there isn’t some sort of grace period between new codex’s. If the codex drops two days before the tournament am I expected to simply adapt, not only rules wise but make hobby/painting adjustments ?

I’ve been really looking forward to this tournament and would be crushed to not be able to use my current list, not to mention I have no idea how I could practically adapt on such notice.

Thanks in advance for any feedback !