Metro D (blue color) will be completed in 2022. But more exciting thing is metro A's extension current Motol to airport. Not sure when it will be completed.
Construction starts on Prague’s long-delayed metro D line - Prague, Czech Republic
Prague’s Driverless Metro D on Schedule for 2022 - Prague, Czech Republic
The first section of the Line, which will stretch for eight stations between Pankrác and Depo Písnice, is set to be completed by 2022.