Katy Perry, Austin Butler, Sia Bring Met Gala Vibes to Beverly Hills House Party

Here's Katy Perry, Austin Butler and Sia making fashion statements worthy of a Met Gala appearance ... only they're not in New York, they're at a Bev Hills mansion party.

The guest list for a Sunday dinner party at investor Michael Kives' $14 million Bev Hills estate rivaled Anna Wintour's annual fundraiser ... with Katy, Austin and Sia being just the tip of the Hollywood icon iceberg. The party was to celebrate the start of Milken Conference, which is a big deal in the finance world.

Oprah and a very colorfully-dressed Gayle King were in the house ... breaking bread with Kris Jenner, Jimmy Kimmel and Chris Pine.

Austin had supermodel Kaia Gerber on his arm, and they were a bunch of other celeb couples ... we're talking Jeff Bezos and Lauren Sanchez, Arnold Schwarzenegger and Heather Milligan, Larry David and Ashley Underwood, plus Jerry and Jessica Seinfeld.

Michael's party, celebrating his investment firm, also welcomed L.A. Mayor Karen Bass and Miami Mayor Francis Suarez ... plus Bill Maher, Nicholas Braun and Matt Bellamy.

Most of the celebs walked out with what appeared to be SKIMS gift bags ... which makes sense, because Kris Jenner helped host the party.