Lauren Sanchez Sports Tiny Bikini for Jet Skiing with Bezos, Kim Kardashian

Lauren Sanchez is working on her summer tan ... 'cause she and her man are jet skiing in Greece, and she's letting it all hang out in a barely-there bikini.

The soon-to-be wife of Jeff Bezos hit the Aegean Sea Friday alongside her billionaire man, and her new bestie Kim Kardashian.

Talk about confidence ... it's not often we see celebs going toe-to-toe with Kim in the bikini game, but Lauren didn't back down. In fact, she didn't even risk wearing a life jacket -- like her fiancé did -- probably because it would've concealed her gym-toned bod.

It's just another incredible vacation in the couple's globe-trotting lifestyle -- as you know, the 2 regularly hit the Mediterranean on Bezos' superyacht, soaking up the rays and inviting the rich and famous to hang out.

We told you yesterday about Kim K, Kris, Kendall Jenner and Bad Bunny meeting up with Bezos and Sanchez in Greece ... so, these new pics are just further confirmation the crew's enjoying some R&R, rather than talking biz.

No news yet on where the group may go together ... but, with Bezos' yacht at their disposal, we expect we'll see Lauren and her gold bikini all over Europe this summer.