The adventures of the Guardians of the Galaxy will continue next year. While celebrating Mantis' actor Pom Klementieff's birthday on Instagram, Chris Pratt let it be known that Guardians of the Galaxy Vol. 3 will begin filming sometime in 2019 and that he was excited to be filming with her. Previously, it was hinted that the third film would start shooting early into next year.
Thus far, the only information to go on is that Guardians Vol. 3 will take place after the events of Avengers: Infinity War. As many fans on Pratt's page have commented, his post does confirm some things about Infinity War and its currently untitled sequel. The third film is also expected to bring Adam Warlock into the fold, who was first teased during one of the post-credit scenes for Guardians Vol. 2.
Right now, Pratt, Klementieff and Rocket Raccoon's Bradley Cooper are the only ones that are confirmed for Guardians Vol. 3. That said, the events of Infinity War don't take other cast members such as Vin Diesel's Groot or Zoe Saldana's Gamora out of the running to return once the Guardians and Avengers have truly defeated Thanos.
Guardians of the Galaxy Vol. 3 will release in theaters in 2020.