AEW signed wrestlers to several different types of contracts, according to Dave Meltzer on Wrestling Observer Radio.
Some wrestlers (unspecified) have “completely exclusive” contracts, but many were signed to partly non-exclusive deals, with the overall idea being that AEW wanted to be fair and wrestler-friendly.
For example, Joey Janela (and likely others) will be able to work for certain indie promotions.
Also, Chris Jericho will be able to work for NJPW and on his cruise.
Daniel Bryan signed a new WWE contract in September, so he won’t be going to AEW anytime soon.
AJ Styles, however, is someone whose contract is up soon. He’s signed with WWE through April 2019 and has been in negotiations for a new deal. He is reportedly seeking a reduced schedule, similar to the deals that Randy Orton and Daniel Bryan currently have, where he would work most television dates, but have reduced live show dates.
Styles is friends with the AEW guys and they would likely make him a very good offer with a much easier schedule, so he’s in a good position right now with a lot of leverage.
Styles is reportedly in the top 1% as far as pay in WWE, though, and WWE has a lot of money right now and they will definitely try their best to make sure he stays.
AEW, and the Young Bucks specifically, definitely want Pentagon and Fenix, according to Dave Meltzer, but they’re working for Impact and MLW, so it’s a “tricky thing.”
In September, MLW announced that the Lucha Bros were “committed [to MLW] through the end of 2019 at the very least,” but that likely mostly means that they won’t go to WWE. AEW could be another story.