The Windows edition of Ace Combat: Assault Horizon has been patched to remove the aerial combat game's reliance on the Games for Windows LIVE service, and replace it with Valve's Steamworks services (thanks VG247). Here's word from the Steam Community forums:

Dear Ace combat fans,
you can now update your Ace Combat Assault Horizon Enhanced Edition for PC game to replace the Games for Windows Live functionalities with Steamworks functionalities. The update is available from today – February 24th and will let you keep both your saves and achievements. Please visit http://steamcommunity.com/app/228400/discussions/ to read the update process.

If you played or are currently playing Ace Combat Assault Horizon, you will be able to update and keep your achievements and saves between February 24th and April 1st. From April 1st, the new version using Steamworks functionalities will become the default version of the game.