How is AT-AT properly pronounced in the Star Wars canon? The iconic four-legged walker was first introduced in The Empire Strikes Back in 1980. Since it has been given a proper label, debate has raged about how AT-AT is said, enveloping a fandom with a fixation on arbitrary details. In a franchise full of abbreviations, this one is without a doubt most hotly discussed of them all. Forget the AT-ST, the AAT, STAP, or any walker or starship in between, here the spotlight is on the Imperial All Terrain Armored Transport.
Following the AT-AT's debut during the battle of Hoth, it has appeared in several Star Wars properties, from TV to movies to even video games, which all lack collective consistency in regards to how its abbreviated form is properly said. In the majority of media it is included in, or at least talked about, it is often simply referred to as an "Imperial Walker." However, things get a bit more muddled once individuals speak of it in terms of its acronym, thanks to a lack of continuity across narratives.
In some instances, like in Jedi: Fallen Order for example, on Kashyykk Cal Kestis opts for the "at-at" annunciation. Meanwhile other properties, such as Star Wars Rebels go for "A-T-A-T" instead. This of course leaves fans in the dark as to which is the true, canonical choice. Hence why there is such an enduring debate as to which is the correct choice in the Star Wars canon. After all, there isn't really a reason for it not to be called one thing or another, so why is there so much fluidity surrounding it?
This is not a topic that Lucasfilm or its story group has dwelled on. The closest thing to a definitive conclusion on the subject came back during an interview at Star Wars Celebration 2016. Rebels and Star Wars: The Clone Wars showrunner Dave Filoni addressed the controversy, saying "You can say at-at, you can say A-T-A-T, and you can say walker. I'm for all three. [...] That's canon because in the show I have imperials say walkers, I have them say at-at, and I have them say A-T-A-T."
Essentially, the pronunciation is entirely situational. It is dependent on who is saying the word and which one they are written to use. As for those not in the Star Wars universe just looking to discuss the piece of Imperial hardware casually, there is no right or wrong to be considered. All three are used interchangeably throughout the always expanding Star Wars canon, so therefore they are all correct. Will this be the final word on this saga? Of course not, but if nothing else there is some form of confirmation that there is no incorrect way to go in saying AT-AT.