Is black-tie engagement party really a surprise wedding for Gwyneth and Brad?

Ryan Murphy is throwing a black-tie engagement party for Gwyneth Paltrow and Brad Falchuck this weekend, Page Six has exclusively learned.

The dress code had some showbiz insiders buzzing that the event could be a surprise wedding. We hear that 400 friends, family and Hollywood A-listers are expected.

Valentino fashion fixture Giancarlo Giammetti sparked speculation of the secret nuptials when he posted an image of the couple on Instagram on Friday and wrote: “These two beauties inside and out get engaged tomorrow!!! All my best wishes my dear @gwynethpaltrowand @bradfalchuk love you and miss not to be there with you!!!”

Comments back included: “I think she was keeping this a secret lol” and, “Does he mean they get married?”

But we’ve also heard rumors Paltrow and Falchuck will actually walk down the aisle later this year in the Hamptons.

Either way, Murphy — who will host the shindig with husband David Miller — has reason to celebrate these days himself, and certainly has the cash to splash out on a party worthy of Goop guru Gwyneth: He just signed a deal with Netflix that’s reportedly worth up to $300 million. Falchuck and Murphy together created hit series “Glee” and “American Horror Story,” and are reportedly behind upcoming Netflix series “The Politician” with no less than Barbra Streisand, Paltrow and Broadway sensation Ben Platt in talks to star.

Paltrow will be arriving fresh from a VIP bachelorette party in Cabo, Mexico, with pals including designer Stella McCartney and Cameron Diaz. Page Six exclusively reported on the girls trip this week, before Paltrow was seen headed to a private jet to depart for female festivities.

Since Paltrow eloped with husband No. 1, Coldplay rocker Chris Martin, she’s treating this wedding as her first and is pulling out all the traditional stops. She told People after announcing her engagement in her own Goop magazine’s “Sex & Love” issue: “I’ve never had a wedding before… So even though I’m 45, I sort of feel like a 21-year-old.” She added: “It’s kind of fun to talk about with my girlfriends. They send me pictures of dresses — they’re as excited about it as I am.”

For her Mexico bachelorette trip, sources told us that pal Diaz booked a private jet for a dozen guests to fly down.

Paltrow’s famous friends include Reese Witherspoon, Drew Barrymore, Beyoncé and Kate Hudson.