Sources with direct knowledge tell TMZ ... the singer is leaving both Scooter and his management company, HYBE. One source put it this way, "Scooter's team is spinning the story. Ariana is leaving both Scooter and Hybe. There is absolutely no truth to her staying."

Scooter has been managing Ariana for years, and she's one of his biggest clients.

Ariana's departure comes on the heels of another big-name exit for Scooter ... Demi Lovato already peaced out. Idina Menzel also left back in January.

Ariana has unfollowed Scooter on social media, so it doesn't seem it's particularly amicable.

Braun has said he's stepping back from day-to-day management and, as we reported, he was negotiating with several clients, including Ariana, for a new structure ... but Ariana says she's now gone.

There have been rumors Justin Bieber might be leaving, but we're told Justin is still under contract with Scooter's company and they are negotiating a possible new deal. We're told Ariana might still have an existing contract with Braun so we don't know how that will play out.

Ariana's a big name on the open market now, and it will be interesting to see who becomes her next manager.