I'm citing Ace of Spades HQ, who is citing broadcast Fox News, but there are other reports. McCabe's name appeared frequently in the Page-Strzok texts as involved in the Hillary email investigation and the Trump-Russia investigation, despite claiming he was not involved with either. He was claiming not to be involved with them because he was definitely involved with his wife's campaign for political office that drew over half a million dollars in campaign funds from Terry McAuliffe, a Clinton associate, and others. Note that although he is leaving his duties "voluntarily", he is leaving them immediately. He will remain on paid leave until he is eligible for retirement (in March).
This is about as close to firing someone as it gets in government service without paying lawyers. If he wasn't fired, he's stepping out before the House votes to release the memo in hopes of avoiding fallout from it. That vote is scheduled for 5pm today.