An SDK by Microsoft doesn’t seem to be public facing, just embeddable controls, but maybe it’s on the roadmap.
These are the ones used by Microsoft’s UWP Map Control (as seen in the Windows Map app) and their (now deprecated) Unity Maps SDK. Superior quality to Google’s where they exist, and in also in areas where Google don’t have 3d tiles.
These have the Aerial view style with the photogrammetry, rather than just the ‘2d’ satellite and birdseye views that Bing Maps/Bing Maps v8 SDK have.
(3d buildings turned on in Google image, btw, just not in this area which is about 40 miles from a Microsoft 3d City)