Ben Affleck and Matt Damon appeared in high spirits as they chatted it up at the SXSW Film & TV Festival over the weekend for the premiere of Ben's new film "The Accountant 2."

The video says it all ... the longtime pals are seated next to one another as they laugh and smile while conversing. BA is quite animated as he pokes MD to get his point across.

Ben is grinning the entire time ... which -- as fans know -- comes infrequently. Nothing against the "Argo" star ... he even addressed his "resting bitch face" on "Jimmy Kimmel Live" back in 2023.

Cheerful Ben paid his friend Mark Cuban a visit inside the theater, too. They appeared to have a playful exchange before Ben hugged a well-dressed individual and eventually found his own seat.

Ben stars in "The Accountant 2" ... reprising his role from 2016's "The Accountant" alongside Jon Bernthal.

Ben and Matt co-produced the film with their company, Artists Equity.

The dream team also walked the carpet together ... with Ben telling press working with his bestie is a "beautiful thing" considering they don't have many friends. He also gushed that he's "lucky" to have such a "good" pal in Matt. How sweet!