1:40 PM PT 6/6 -- Our sources say the two aren't dating or anything serious ... they were just having some fun while out with friends. We're told there's no bad blood with Kendall, Bella and Gigi.

Kendall Jenner is living her best (single) life -- kickin' it with NBA star Ben Simmons one day ... and locking lips with Gigi and Bella Hadid's brother the next.

Kendall was spotted smack-dab in the middle of a heavy makeout sesh early Tuesday morning with Anwar Hadid at a CFDA Awards after-party in NYC. You can tell it's him from the bleach blonde hair he was sporting at the event. Plus, Kendall took a photo of his tattooed hands herself.

Eyewitnesses tell us Kendall was hangin' with Anwar at Socialista New York for about 2 hours -- kissing, cuddling and drinking with the youngest Hadid sibling the whole time. She ended up heading back to her hotel by herself around 4 AM or so ... no Anwar in sight.

WHATCHA HIDING?
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Remember, Kendall was on a bike riding date with her rumored new flame, Ben, the day before in L.A. They've been hanging together a lot lately ... post-Blake Griffin. As for Anwar, we're told he and his gf split last month.

And, get this ... nearly two years ago, Kendall posted a pic with Hadid -- when he was just 17 and Kendall was 20 -- and the caption, "dibs?"

What makes this especially interesting ... Kendall has never -- as far as we can see -- shown this level of PDA with the people she's dating.