https://www.gamespot.com/articles/gta-5s-red-dead-redemption-2-mission-confirmed-her/1100-6455679/

With Red Dead Redemption 2 slated for release next spring, Rockstar is ready to begin drumming up interest in the game among Grand Theft Auto V players. Following the discovery of some kind of RDR2-related content in GTA Online files, Rockstar has officially announced the details of a new crossover mission and weapon that launches today.