The 185-pound contest will take place at a location to be determined.
Whittaker (22-5) lost the middleweight championship to Israel Adesanya in October 2019, but bounced back in a big way in 2020. The Australia-based Whittaker defeated Darren Till via unanimous decision in a five-round contest in July, and Jared Cannonier in a three-round bout in October.
Costa (13-1) is coming off the first professional loss of his career, a second-round TKO to Adesanya for the middleweight title in September. There had been some discussion about Costa moving up to the 205-pound division in the near future, sources told ESPN, but he remains focused on 185 for now following that loss.
Adesanya is still the defending champion, although he will move up in weight in his next bout to challenge light heavyweight champion Jan Blachowicz on March 6.