Ashton Kutcher later stated that he originally turned down the cameo offer in the first episode, but then his wife and fellow original series alumnus Mila Kunis highly encouraged him, saying "Y'know we owe our entire careers to this show, it doesn't matter what the script is, we're doing it" and they both did their cameos.
Original series regulars: Topher Grace, Laura Prepon, Mila Kunis, Ashton Kutcher, and Wilmer Valderrama all made appearances, reprising their roles from 70s show (1998).
In one of her last interviews, Tanya Roberts, who played Donna's mother in the original series, stated that she would be willing to appear if the series got a revival and she was asked. Sadly, Roberts passed away in January 2021, eight months before the revival was announced.
Parts of the furniture in the basement used to be in That 70s Show's living room.
Because the actors playing the teenagers on the show were not actually born until after 2000 they spent some time with the legacy cast who helped them with 1990s era stuff. Topher Grace in an interview said that he helped some of the younger cast and that it was kind of full circle since the original cast did the same since most were either not born or very young during the 1970s.