Russell Westbrook -- I'M ENGAGED ... With $700k Ring! [Update]

10:06 AM PT -- IT'S A $700,000 RING!!!!

We've learned ... it was made by Jason of Beverly Hills ... who's made engagement rings for all sorts of stars including Gabrielle Union and Evelyn Lozada.

As for Russell's ring -- we're told it's a 6-piece elongated cushion cut ring with VVS clarity ... and in total, the whole thing is worth $700k.

We're told Russell knew exactly what he wanted when he hit up Jason's shop. It was very important to him that he got a ring with the highest quality possible.

Dude did a helluva job.

Oklahoma City Thunder star Russell Westbrook is the next NBA star in line for a wedding -- 'cause he popped the question last night ... with a massive diamond ring ... and his GF said yes!

Westbrook and longtime GF Nina Earl made the announcement on social media Wednesday night ... showing off the gargantuan rock with a caption that read, "Nothing even matters..@ninamri3_ forever my lady! LOVE YOU!!!!"

Earl is a former UCLA basketball player -- and the two met during their college days ... before Westbrook signed his $80 MILLION contract extension.