Tomb Raider: Definitive Edition was originally scheduled to release for Xbox One and PS4 on January 28th, but it looks like Gamestop has decided to start selling copies a couple days early.
Yesterday afternoon I received an email from the Gamestop Powerup Rewards program informing me that Gamestop stores nationwide were now selling the Definitive Edition of Tomb Raider. Even after this very official email I was still a little skeptical, so I called my local store for confirmation. The email was 100% correct. You can go purchase Tomb Raider: Definitive Edition from any Gamestop right now.