He very well might be... it's difficult to judge one way or another really. It depends on which article you read sometimes.
Two things prompted my unconfirmed take on the matter that he might be calling it quits; the closing scene in Spectre, which I won't disclose as to not spoil the ending, only to say that it kind of appeared to be a subtle statement to his fans in the manner in which it played out. And the other thing was a comment he made shortly after Skyfall had released, where Craig said, "I'd rather slit my wrists than do it again."
Of course, he didn't slit his wrists and he obviously accepted the role to do Spectre.
Whether he's had his fill or possibly not quite yet finished - history indicates that the average term for an actor to stay active in this role is roughly 10 years, and unless there's a production not being talked much about coming up for release later on this year (which is highly unlikely) - Craig will be entering his 11th year as the main character in 2017. In other words - the writers are probably already looking for an answer to the "who's next" question, regardless of what seems to be at the very least some indecision coming from him on the matter at the moment.
Rumors surfaced a couple of years ago that Denzel Washington was actively considering to be Craig's successor, but he said that they started because of something he jokingly said, at least more so than there being any real seriousness about it. That said, he did seem to indicate that he wouldn't automatically turn the opportunity down if he were approached about it, certainly leaving the door open.
Suffice to say - it would be very interesting to see how well an African American version of Bond would be received. I personally think he could pull it off in a big way, but at 61 years of age - the question is more about whether he would want to take on the usual modern-day stunt work that tends to befit someone considerably younger. Craig is 47 years old, 14 years younger, btw.