The movie star was on the red carpet for the premiere of his producer sister Karina Miller's film, "Semper Fi", in West Hollywood on Tuesday night (September 24), when he was asked about "The Matrix 4".
He wasn't giving much away but told Entertainment Tonight, "It's very ambitious - as it should be."
Miller then stepped in to remind the media it was her big night and brother Keanu was just a guest.
"He's always been so supportive and so protective of me doing my own thing and that I will always really appreciate," Karina said.
The "Semper Fi" cast, including Leighton Meester and Jai Courtney, joined the siblings at the premiere for the film, which proud brother Keanu called "a great accomplishment", adding, "It's a wonderful film."
Reeves and Carrie-Anne Moss are reprising their roles as Neo and Trinity in "The Matrix 4", while Lana Wachowksi, who directed the first three movies with sister Lilly, is directing again. The movie is expected to begin filming in early 2020.