I've been listening to a couple of Podcast interviews Bob Caro has done with Preet Bhara and Conan O'Brien. Both are recommended.
The memoir he refers to is finished. It's called Working: Researching, Interviewing, Writing. Unlike the rest of his books, it's short. Having not read any of his other books, I found it fascinating and I highly recommend it.
Working is great, but it is not the full memoir. My understanding is that he compiled "Working" so that some important pieces are published in case he doesn't get to finish his memoir, which unfortunately seems somewhat likely.