The PC version of Mafia 1's remake Mafia: DE, announced last week, will be a temporary exclusive title for Steam. This is what the description on the official website of the series suggests. The game is also available for pre-order in Epic Games Store, but will be released there later. However, 2K Games has not disclosed how long this exclusivity period will last.
As a reminder, Mafia: Definitive Edition will appear on August 28 on PC (Steam), PlayStation 4 and Xbox One. Mafia II: Definitive Edition and Mafia III: Definitive Edition debuted on May 19 and were made available for free to owners of previous versions.