The Everlong band treated 900 lucky fans to a surprise show at the Fremont Theater in California on Saturday, their first since 2024.
Former Nine Inch Nails percussionist Rubin has swapped groups with Foos' Josh Freese.
Rubin was officially sworn in at the concert by frontman Dave Grohl, who told the crowd: "Everybody else has said it, I finally get the opportunity to say, ladies and gentlemen, will you please welcome, the most badass mother******, Ilan Rubin, is playing drums in the Foo Fighters. It's official."
The band played a 25-song set and dusted off Exhausted and Have It All, which have not been performed live since 2014 and 2015 respectively.
Freese, who served as Nine Inch Nails' sticksman between 2005 and 2008 before being replaced by Rubin, previously confirmed he had returned to the Trent Reznor-fronted group.
"Being back on tour with Trent and the crew - helping them do what they do best night after night - is something I'm incredibly excited about," he posted on social media.
Freese stepped into the role for Foos after the 2022 death of their longtime drummer Taylor Hawkins.
Meanwhile, Grohl and co have recently teased fans about their return to the studio.
The Learn to Fly group's last studio album was 2023's But Here We Are, their first without Hawkins.
The band took to social media to call on their fans to "assemble", and directed supporters to sign up for their newsletter for "info you won't want to miss".
The Monkey Wrench hitmakers followed that up with a picture of Grohl, bassist Nate Mendel and guitarist Pat Smear jamming in their recording studio Studio 606.
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