The welterweight bout has been signed, according to Thiago on TATAME.com.
"He has solid wrestling, knows how to fight standing, is good [with] takedowns and knows how to fight on the grou,d but we'll do a good job to annull it," Thiago said. "It'll be a chess fight again."
Thiago (11-0) pulled the upset over Koscheck with a first-round TKO win at UFC 95 on Feb. 21.
In his last fight, Fitch (18-3) playfully stole Akihiro Gono's wig during weigh-ins and defeated the following night defeated the PRIDE veteran via unanimous decision. Fitch fought for the title last August in a losing effort against champ Georges St-Pierre.