Starfield's first DLC expansion has already been revealed

techradar.com:

We already know of Starfield's first DLC expansion, thanks to a blink-and-you'll-miss-it reveal during the Starfield Direct during E3 2023.

The first StarfieldDLC expansion is called Shattered Space, and it was revealed to be a part of the game's big collector's edition, known as the Constellation Edition. It'll also be bundled with the Digital Premium Edition, should you not wish to spend a king's ransom on a rather fancy-looking smartwatch.

We have yet to receive details on the Shattered Space expansion, but as it's already been confirmed, it's easy to imagine it will launch not too long after Starfield's September 6 release on Xbox Series X|S and PC.

Of course, if you just want to play Starfield for the cost of an Xbox Game Pass subscription, you'll more than likely be able to buy the Shattered Space expansion separately. It's currently unknown if this DLC will come to the subscription service day-in-day. 

Both the Digital Premium Edition and Constellation Edition pack in the Shattered Space expansion, as well as five days' early access, a Constellation character skin pack, and digital copies of Starfield's soundtrack and art book. A pretty feature-rich package of extras if you're extra keen on the Bethesda Game Studios title.

If Shattered Space is anything like prior DLCs in Bethesda Game Studios' repertoire, it'll probably be integrated into the game's main story, rather than something you tackle in the postgame. Especially so, considering it's probably going to be the first of many expansions. With that in mind, I wouldn't expect anything too out there. Unless you count the fact the game is set in space. In which case, it very much will be out there.

Still, Starfield being supported with post-launch content is a given,