From Halopedia, the Halo wiki
Pension Plan is an achievement in Halo: Spartan Assault. It is unlocked by the player earning 25,000 XP throughout their career. The achievement is worth 10 Gamerscore on Xbox 360 and Windows systems, and 20 Gamerscore on Xbox One. It is represented by a circle with XP inside it.
If the player has previously unlocked this achievement on a Windows 8 device, it will automatically unlock the first time the player completes a mission in the Xbox 360 version. In the Xbox One version, all 25,000 XP must be earned on the Xbox One.