New Zealand, who will host the British & Irish Lions in 2017, take on Australia next week, shortly after clinching a third straight Rugby Championship title.
Williams has not been named in the squad but uncapped scrum-half Pulu has and the 24-year-old has enjoyed spending some time around the 2011 World Cup winner in preparation for a possible All Blacks debut.
"It's big to have him in, especially for the young fellas," Pulu told 3 News.
"Sonny has fit in really well with the boys and straight into joking and all that, so he's loving it too.
"I'm quite blessed to actually get this opportunity - I'm really stoked. I've always dreamed about being an All Black but I didn't know it would come true.
"I'm quite lucky - there are so many good half-backs in this country and I got chosen so I feel really blessed. The boys are really happy for me and I guess I'm only playing well because of them."