There isn't a default Cepheus setting. It came to be after Mongoose changed licensing terms for Traveller. So Cepheus is a fork of the OGL content for MgT1. A lot of third party publishers had material for that, and pivoted to Cepheus to continue their line.
Kosmic is A Cepheus setting (not The), but you can also have Hostile and Orbital from Zozer, etc. Just search for Cepheus on DTRPG and you'll find plenty. They each have their own twist, so read their elevator pitch.
I messed up a bit. Kosmic is their brand of Cepheus, basically the rules. The setting is called Solis people of the Sun.
This is the blurb:
Traveller is half the galaxy, millennia into the future. Solis is a couple hundred years from now, and a much smaller chunk of the galaxy. It's a different vibe.
Hostile is the retro-future, like the Alien films, Outland, etc.