Portal: Still Alive added 14 new challenges. The Xbox 360 release expanded the original Portal with a bonus set of 14 levels based on the earlier Portal: The Flash Version map pack.
These bonus chambers were separate from the original campaign and introduced additional puzzle layouts and mechanics. Still Alive also added challenge modes, allowing players to replay chambers while being judged on time, number of steps, or number of portals used.
The number can be confusing because the release also included six advanced versions of existing chambers. Those advanced chambers were enhanced versions of Test Chambers 13 through 18, not part of the 14 newly added bonus levels. Counting every extra map or challenge variant can therefore produce a different total.
Still Alive was released for Xbox 360 through Xbox Live Arcade in 2008. Later versions of Portal, including the Nintendo Switch compilation, included some of its bonus chambers, but the original Still Alive package also had platform-specific achievements and other details.