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It seems like they've updated the official site with a FAQ page for the expansion.
#5 is a pretty important one for returning players. Once the new expansion goes live, you can get the other two for free simply by being a subscriber.
1. What is the launch date for Knights of the Fallen Empire?
The official launch date for Knights of the Fallen Empire is October 27, 2015.Players who have been a subscriber from July 31 through October 19, 2015 gain Early Access beginning October 20, 2015, one week before the official launch date.
2. What features will be available during Early Access?
All features will be available at the start of Early Access on October 20, 2015.
3. How do I obtain my Knights of the Fallen Empire Pre-Launch Reward items?
If you has an active subscription from July 31 through October 19, 2015, you will receive your Pre-Launch Reward items via in-game mail at the start of Early Access on October 20, 2015.If you are not eligible for Early Access, you will receive your rewards via in-game mail on October 27, 2015.
4. How do I get the Epic Story XP Boost?
All active subscribers automatically receive the Epic Story XP Boost; the boost expires October 19, 2015.
5. Can I still get Knights of the Fallen Empire if I don’t have Rise of the Hutt Cartel or Shadow of Revan?
All subscribers will receive access to Rise of the Hutt Cartel and Shadow of Revan starting on October 27, 2015.
6. How do I pre-order Knights of the Fallen Empire?
Knights of the Fallen Empire is not available for pre-order as it is free to all active subscribers . You must be an active subscriber to receive the expansion.
7. When will Chapters be released?
Knights of the Fallen Empire will launch with the first 9 episodic Chapters of the story. The remaining chapters will be released monthly starting in early 2016.
8. Is the Outlander a new class in Star Wars: The Old Republic?
No, Knights of the Fallen Empire keeps the 8 core classes, but your character’s story becomes that of the Outlander, a veteran of the Great Galactic War.
9. What if I unsubscribe from Star Wars: The Old Republic after October?
If you unsubscribe after October 27, 2015, you will keep the first 9 Chapters of Knights of the Fallen Empire, but will not receive any additional Chapters when they are released.
10. What if I don’t subscribe until all the Chapters are released?
If you subscribe after the launch of Knights of the Fallen Empire, you will receive all the content that has been released up to that date. However, as a subscriber you are eligible for great benefits that you don’t want to miss out on such as a monthly Cartel Coin grant and access to the full spectrum of character species.