From now through January 4th, 2016, former SWTOR subscribers can log in and play the first chapter of the expansion (The Hunt) for free. This offer does require players to opt in to BioWare’s emails, but on the up side, it also includes the ability to create a level 60 character to keep.
Star Wars: The Old Republic’s recent expansion, Knights of the Fallen Empire, you at least have to subscribe for a month to unlock the first batch of chapters. However, there is another Skywalk… um, way to check it out: BioWare is now offering former subscribers a sneak peek into the expansion with a limited-time trial.
Source: SWTOR. Thanks to I-Spy for the tip!