Clarke has been an ABC News consultant for some time. A search yielded this
ABC News article from August 12, 2003, which mentions Clarke in that capacity (go to that page and look for the word "consultant" in it).
I didn't search for earlier references, so I don't know when Clarke joined ABC, but his employment there goes back at least as far as August, 2003.
Then why are they annoucing it today? And why did CBS get that exclusive interview?
I bet they let him go and hired him back.
This is from today:
""Mr. Clarke has already given 14 hours of testimony to the commission investigating why the government failed to prevent those attacks," said Mr. Stephanopoulos, also noting that Mr. Clarke now works for ABC as a consultant. "