Sebastian Stan and Annabelle Wallis just stepped out for the first time since their baby news dropped ... and yeah, they're looking very good together!

Pregnant Annabelle was glowing during their NYC stroll Thursday -- rocking a flowing black dress that skimmed her bump, while holding hands with Sebastian as they soaked up the day.

The pair were casually making their way to a restaurant ... and after four years together, their ease around each other is evident.

TMZ broke the pregnancy news last month -- and it's all happening during a packed time for both. Sebastian's busy hyping his next Marvel outing, "Avengers: Doomsday," while Annabelle's also got a slate of projects lined up for release.

Still, they're clearly carving out time where they can -- and doing it in style!