The new expansion is coming in summer 2022.
During Capcom's Tokyo Game Show presentation, there was a big focus on Monster Hunter, including new additions to Monster Hunter Stories 2 and Monster Hunter Rise. However, the biggest announcement was new details about Rise's new expansion, Sunbreak.
The teaser revealed last week doesn't show much, showing off the new area that Sunbreak will take place in, and a dragon that resides there. We also get confirmation that it will be available in the summer of 2022. Director Yoshitake Suzuki introduces the dragon, saying that it is a new Elder Dragon named Malzeno. No other details for it were given at the time. Suzuki then started giving additional information for the upcoming expansion.