Late on Wednesday, Michael Seibel revealed on X that he will be transitioning into a “partner emeritus” role after spending over 12 years at the renowned accelerator Y Combinator.

In a separate announcement, Y Combinator CEO Garry Tan published a company blog post, acknowledging Seibel’s extensive history with the organization. Seibel initially joined YC as a founder, completing the program twice – first with the streaming startup Justin.TV and later with the streaming app Socialcam. He subsequently held various roles, including group partner, managing director, and CEO of the YC accelerator.

It’s worth noting that Seibel had already stepped back into a less operational group partner role recently. In a YC blog post last year, he expressed his desire to “hand over my leadership responsibilities,” with the transition becoming “effective” after the accelerator’s winter batch of startups completed the program.

A tenure of 12 years is considerable for anyone, but Seibel’s departure might have been anticipated as early as 2022, when Tan was appointed President and CEO. The move allegedly caught some YC employees off guard – partly due to Tan’s simultaneous management of a separate venture fund outside of YC, and also because they believed Seibel to be next in line for the role.

We have reached out to Seibel for comment. In the meantime, he shared on X that after taking the upcoming summer to relax, he is eager to “help government better serve its citizens.” He added, “Government was the passion of my youth, and I’m excited to reengage.” Seibel concluded by thanking Y Combinator founders Paul Graham and Jessica Livingston for “changing my life.”

This news arrives roughly two weeks before YC’s spring batch of founders begins their program, which will run from April through June.