Russell Westbrook -- I'm Getting Hitched! Doing it Chill in Bev Hills

Oklahoma City Thunder superstar Russell Westbrook is getting a ring even before the NBA season begins -- he's marrying his longtime GF this weekend in a pretty baller setting.

TMZ Sports has learned ... Russell and Nina Earl will walk down the aisle in Beverly Hills on Saturday -- just about a year after they started planning. As we reported, they announced their engagement last September ... when Nina posted a pic of her $700k ring!

We're told the couple is having a low-key ceremony, and wants to keep the exact location under wraps, but trust us ... the wedding pics will be spectacular.

Mazel tov!