I think it'll have 1GB. It will probably have the A9 SoC, which has only had 1GB of RAM in any product.
Plus, where people seem to complain about 1GB not being enough is with loading full desktop-size websites on Safari, multitasking away from those sites, and being annoyed that they reload when returning to Safari. That is not a usecase on AppleTV. There probably won't be a Safari browser, and I doubt there will be any significant multitasking.
The most multitasking AppleTV will do is likely the picture-in-picture features demoed in iOS9. Those features work on devices with 1GB.
That said, I hope it has more. Moar! MOAR! But I'm going to buy it regardless. I know it. You know it. Apple knows it.