Marvel Comics' Editor-in-Chief C.B. Cebulski says the company plans "an exclusive announcement" on Friday, as well as name more creators involved with its mystery August 2019 project(s). All that, and some art.
Cebulski didn't specify if "exclusive announcement" meant the announcement of a new creator under a new 'exclusive' agreement, or if it was something else. The "exclusive announcement" could mean an announcement made exclusively by Marvel Comics, likely related to the creative teams named in the "ads and tweets" Cebulski mentions.
Given Cebulski's past as Marvel's globe-trotting talent scout however, it's also possible the announcement could be a new creator or creators going Marvel exclusive. Superman artist Patrick Gleason was announced as a Marvel 'exclusive' creator last weekend.