TPU spreads news that AMD is going to launch a Radeon R9 280X revision towards the end of November. The reason why the card is getting an update is because the card was launched with the Tahiti XT2 GPU, the same chip that drives the Radeon HD 7970 GHz Edition, because the revised Tahiti XTL that was intended for the Radeon R9 280X wasn't ready for an early-October launch.
The new Tahiti XTL chip promises lower power consumption, it will run cooler and have a lower noise output.
Unfortunately, there will be no way to distinguish this card on retail shelves. AMD plans to perform a "running change" for its add-in board partners, which means Tahiti XTL models will be sold alongside the older Tahiti XT2 models. There will be no way to tell which version you have without reading the BIOS or disassembling the card.