Breaking Bad - Interview with Bob Odenkirk

Are you shooting the fifth season of Breaking Bad yet?
No -- shooting starts in May, I believe. I usually go and visit the writers' room -- I have not done that yet, but I will soon. So I know nothing. I don't even know if Saul Goodman returns. I'd like to believe he will. But we will see. I never know anything about that show in advance; in fact as the season goes, they black out the scripts, so I literally don't know what is happening in the show, even while I'm doing it.

Are any of Saul's lines ad-libbed?
No. I do what they write, and I do it pretty exactly. You were asking about variety earlier, and honestly I've never had a role that I have approached as formally as I approach Saul Goodman. I learn those lines verbatim and I rehearse a lot. I get really ready for that part. I am purely an actor on that set. It's a challenge and a hoot and a relief all at the same.

Source: Full interview @ SF Weekly