Starship upper stage will have 6 engines. 3 sea level raptors which it's currently fitted with and 3 vacuum raptors.
Here's a picture of the two side by side, current versions that was posted some time back. Same engine more or less, just a fuckhueg nozzle on the vacuum raptor for optimal vacuum operation. You could fire it in an atmosphere. It's not good for longevity of the nozzle (primarily) and the engine though.