Sovereign

The Western Motorcycle Company Sovereign is a motorcycle that is featured in GTA 6.

The Sovereign previously appeared in GTA 5 and GTA Online, where it was added as part of The Independence Day Special update in July 2014. 

Therefore, this is the first time that the motorcycle has ever appeared as part of a Grand Theft Auto title's vehicle roster at launch. 

The Sovereign first appeared in Trailer 1, near a car meet in Vice City. It was more clearly revealed in an official screenshot of Ambrosia County, being ridden by a member of the Final Chapter MC.

Since its last appearance, the motorcycle has seen some minor design changes. Most notably, the bike is missing its iconic American flag livery, but it also appears to have lost its rear top box.

It is possible that this motorcycle is a new vehicle entirely, simply based on the Sovereign. With that in mind, it could have a different name altogether. 

The Sovereign is already essentially a civilian variant of GTA 4's Police Bike, which is based on the real Harley-Davidson Road King FLHP.