Los Angeles, California - Oppenheimer took top film honors at the Screen Actors Guild Awards on Saturday, as Hollywood stars partied at their union's first prize-giving gala since staging its longest-ever strike last year.

The prestigious prize for best performance by a cast at the SAG Awards is historically a strong predictor for the Oscars, and makes Oppenheimer a formidable frontrunner for best picture.

Christopher Nolan's epic drama about the father of the atomic bomb also took the awards for best actor for Cillian Murphy, who plays the titular scientist, and best supporting actor for Robert Downey Jr., portraying his bitter rival.

"Thank you for the invitation to play a genuine part in making this scarily important film," said Kenneth Branagh, speaking on behalf of the cast.

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The mood at the gala was celebratory all round, as members of SAG-AFTRA – the union that represents some 120,000 performers, including A-list stars – congregated in numbers for the first time since the strike ended in November.

Branagh recalled how the film's cast had walked out of their London premiere last July as the work stoppage was about to begin: "We went from the red carpet and we didn't see the film that night. We happily went in the direction of solidarity with your good selves."

"So this, this is a full circle moment for us," he said, to loud applause.

The guild ultimately extracted hard-fought gains including better pay and protections against artificial intelligence (AI) from studios including Disney and Netflix.

"You survived the longest strike in our union's history with courage and conviction," said SAG-AFTRA president Fran Drescher.

Warning that AI could "entrap us in a matrix where none of us know what's real," Drescher said "seminal" gains made in talks would "set the trajectory for many generations to come."

Oppenheimer has been relentlessly scooping up awards all season.

The movie has already won top prizes at the Golden Globes, Critics Choice Awards, Directors Guild of America Awards, and Britain's BAFTAs.

It now adds the top SAG-AFTRA award for best cast, which has led to recent best picture Oscar wins for movies such as Parasite, CODA, and Everything Everywhere All at Once.

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Many of the same actors who vote for the SAG Awards also make up the largest voting bloc for the Academy Awards, which will be held this year on March 10.

Oppenheimer saw off Barbie, Killers of the Flower Moon, American Fiction, and The Color Purple for top honors.

In the best actress category, Lily Gladstone (Killers) bested her main rival Emma Stone (Poor Things) in a closely watched result that throws that Oscars race wide open.

The Indigenous actress, who portrays an Osage woman being exploited by nefarious white neighbors in Martin Scorsese's 1920s-set epic, began and ended her acceptance speech in her native Blackfeet language.

Supporting actress prizes have been going consistently this season to Da'Vine Joy Randolph (The Holdovers), and Saturday's gala was no different.

Barbra Streisand received a lifetime achievement award, earning a rapturous standing ovation in a rare public appearance for the 81-year-old.

The night also honored television. The Bear took comedy wins for its overall cast, and for stars Jeremy Allen White and Ayo Edebiri.

Succession won the drama series cast prize, while Elizabeth Debicki won best actress for The Crown for her portrayal of the late princess Diana.

Pedro Pascal took best actor for The Last of Us, admitting he was drunk as he became one of many performers to take advantage of the Netflix telecast's relaxed tone – and different rules on what is permissible – by dropping an F-bomb.

The 30th SAG Awards became the first Tinseltown award show to stream globally on Netflix.

The streamer has been cautiously moving into the live events space in recent years, with a Chris Rock comedy special and a celebrity golf tournament.

Moving to Netflix from smaller cable networks TBS and TNT gave the SAG Awards access to the streaming giant's 260 million-strong subscriber base – and meant no commercial breaks.

"Personally, I can't wait to get home and have Netflix recommend this show to me based on all the other stuff that I've watched myself in," joked Idris Elba, who opened the gala.