Is the implication of the statement that "I will testify about <whatever> in exchange for immunity" a tacit admission of criminal guilt?

I was reading about the latest adventures of Michael Flynn, who was fired from the White House a month ago for lying. He has since gotten himself in even more trouble.

Last night, it was reported that he had been saying that he would testify in exchange for immunity.

Is he basically saying “I’m guilty but I want to get something out of it”? Can he ever claim innocence after this?