Marshall Allen turned 101. And André 3000 was invited to the cosmic party in South Philly.

Marshall Allen celebrated his 101st birthday in South Philadelphia in exactly the way you would expect from the saxophonist and leader of the Sun Ra Arkestra: By leading a joyous, mind-bending free jazz band that traveled the interstellar spaceways in his own inimitable, improvisational style.

And this band, which held forth for two hours in the back room at Solar Myth on South Broad Street in the early hours of Sunday evening was a unique one, with a special guest.

André 3000, the OutKast rapper soon to be inducted into the Rock and Roll Hall of Fame, has taken a late career left turn as a flautist, and now is also a piano player inspired by the spirit Afro-Futurist experimentation that Allen has long embodied at the helm of the Germantown-based Arkestra.

On Sunday, the rapper turned jazzman — who was born Andre Benjamin — took a place at stage left, by a grand piano, where he played a variety of flutes, crouched down and fiddled with floor pedals, and occasionally stuck his head under the piano lid and banged on the strings.

(Earlier this month, Benjamin appeared at the Met Gala with a toy piano strapped on his back, which turned out to be a way of announcing his new EP 7 Piano Sketches.)

Benjamin joined Allen and a band that included Arkestra trombonist Dick Griffin, drummer Austin Williamson, and percussionist Carlos Niño in an evening that was hosted by Allen’s son, Ronnie Boyd, who led a chorus of “Happy Birthday” and a Champagne toast.

He also attempted to bring on guest speakers to pay tribute to his father, who made that task difficult because he would not stop playing his alto saxophone and EVI (electronic valve instrument), both of which he performed with astonishing verve.

“When you’re 101, you get to do whatever you want,” Boyd said with a laugh.

Guests in the house for the party, which was produced and presented by the Ars Nova Workshop, included Sun Ra biographer John Szwed and Philadelphia ambient composer Laraaji, and Philly Specials producer Charlie Hall, as well as Pennsylvania State Rep. Rick Krajewski and André Carroll, the latter of whom expressed amazement after seeing Allen play for the first time.

Allen plays once a month at Solar Myth with his rotating band Ghost Horizons, with whom he had performed on Friday night, celebrating the release of a brand new in-concert album, Live in Philadelphia, with the Ghost Horizons ensemble.

Krajewski said that he had seen “The Maestro” at the venue many times and talked about Allen’s commitment to freewheeling artistic exploration over a staggeringly long period of time.

“When I watch Mr. Allen and I’m witnessing him play, I feel like I am witnessing Black expansiveness,” Krajewski said. He’s saying, ‘I bear no allegiance to these narratives. I don’t believe in this box.’ And that is inherently a liberatory act, that is an act of political resistance. And so I want to thank Mr. Allen for showing what Black expansiveness is.”

Earlier this year, Allen — who has released scores of recordings with the Sun Ra Arkestra — released a solo album, with his recording New Dawn.

» READ MORE: Remembering out-of-this-world jazz man Sun Ra with Marshall Allen

Now, he’s ready to follow that with 101 An Audio Odyssey, which is soon to be released by the Third Way Cultural Alliance. The album is produced by, and features, Philadelphia virtuoso bass player Jamaaladeen Tacuma as well as Wilco guitarist Nels Cline and Philly sax player Immanuel Wilkins.

Tacuma also took the stage to pay tribute to Allen, who made him go fetch his bass and come back and join the jam. The same happened with Arkestra singer Tara Middleton, who came to praise Allen and wound up singing with him.

Because when you’re 101, you get to tell people to do what you like.