The schools could be approved for admission as early as a Sept. 10 meeting of Big 12 presidents, according to Sports Illustrated, which first reported the story.
"Things are moving very quickly," one source told ESPN on Friday. "There's obvious momentum to get votes to the board."
American Athletic Conference bylaws require schools to give a 27-month notice before they leave and pay a $10 million buyout fee. In that scenario, joining by the 2023 season would be a long shot, but an earlier exit and higher buyout could be negotiated. The most realistic timeline, sources said, is 2024.
Sources in the American told ESPN that Houston, UCF and Cincinnati haven't officially informed the conference of their intent to leave.
ESPN reported Thursday that officials from the four schools had informally contacted the Big 12 about membership.
"All of those schools reached out to us," a Big 12 source with knowledge of the discussions said. "It wasn't like we poached them. They all made the initial communication."
The Big 12 presidents are expected to meet next week, but a conference source said it might be only eight presidents for their regularly scheduled meeting. A vote on new membership requires the presence of the full board, a source said, which still includes Oklahoma and Texas. The Big 12 is expected to have the eight of 10 votes needed to officially accept the schools into the conference.
Oklahoma and Texas have said they will honor their grant-of-rights agreement before joining the SEC on July 1, 2025. If that holds true, it's possible the Big 12 operates as a 14-team conference for a year, with the new members competing alongside the outgoing conference co-founders. It's also possible BYU, an FBS independent, joins the Big 12 before the American schools.
Big 12 commissioner Bob Bowlsby declined comment Friday.