It hasn't been formally announced, but Konami will be publishing a special 25th anniversary edition of Metal Gear Solid 4 for the PlayStation 3 later this year.
The existence of the release was discovered when it appeared in inventory systems of two UK based game retailers, which Eurogamer reported not long after.
Not much is known at the moment, though it will only be a matter of time before Konami finally comes clean. It is assumed to be a re-release of the original game, along with all the relatively recent additions baked in already. Including trophy support and the ability to install the game onto one's hard drive.
Though one thing that is not clear is the price point. Zavvi has the game listed as £37.45 (which is about $59.83 American), while ShopTo has it listed as (or $31.94 American). Quite the difference in asking price.
Oh, and for those wondering why it's the 25th Anniversary Edition, despite the fact that MGS4 came out just four years ago, its in reference to Metal Gear franchise as whole. The very first Metal Gear game came out in Japan for MSX in 1987.