On this page of the Outlast Trials guide, you will find an overview of Program X, which is the last segment available in early access.
How to unlock Program X?
Unlocking Program X is theoretically rather simple. You must complete all previous programs. Both trials and challenges. You don't have to worry, however, about the grade you received for each task. Low scores do not block access to the final stage.
Program X's content
Program X consists of ten objectives. These are all the challenges and trials you have faced in earlier sequences. The only difference here is the difficulty level. Program X is definitely much more challenging.
What's also important - you receive an escape token for completing each challenge. Collecting all ten will allow you to unlock the last sequence in the game.