The long-awaited PC version is set to release worldwide on March 24, 2015. Rockstar would really prefer you didn't wait until then to put some money down, though - that's why, if you pre-order by February 1, it will give you your choice of 11 Rockstar titles (including Max Payne 3, LA Noire, and Grand Theft Auto IV) for free straight away, and $300,000 in GTA Online spending money on release.
Even if you don't act fast enough to claim that offer, you'll still get $1,000,000 in-game cash (split evenly between the single-player campaign and GTA Online) for pre-ordering at any point. That's enough to buy a nice apartment and a sweet car straight away, which is pretty much the Los Santos dream.
Note that this deal is being offered exclusively through the Rockstar Warehouse - not Steam. At least you'll still be able to pre-load before release so you can jump right in to the 4K-compatible, 60-frames smooth crime paradise… assuming your computer can handle it.