To celebrate the 10th anniversary of Metro: Last Light, which was released on May 14-17, 2013, 4A Games is offering the game for free on Steam. This is announced by the official account of Metro Exodus.
From May 18 to May 25, 2023, Metro: Last Light's Complete Edition can be added to your own Steam library for free. It's just not clear which game is meant. There is no Metro: Last Light's Complete Edition Steam page, only a Metro: Last Light Redux, which contains all four DLCs for Metro: Last Light - Faction Pack, Tower Pack, Developer Pack and Chronicles Pack. That is, conditionally it can be considered as Metro: Last Light's Complete Edition.
By the way, did you know that in the DLC for Metro: Last Light there are as many as 7 (!) additional single-player missions, in some of which you play as other characters of the game?