The former Wales boss said: "We have a sequence of four big Tests which will be a significant challenge and a good 'road test' for us ahead of the Rugby World Cup in France.
"We have a short turnaround between major tests against England and France. It is prudent to have additional cover at the specialist positions."
Unless Henry decides to rest key players for the tour, the likely beneficiaries of the extended squad are Southland half-back Jimmy Cowan and Taranaki front-rower Andrew Hore, both third choice in their position.
However, Henry could take Canterbury and New Zealand Maori captain and hooker Corey Flynn instead of Hore.
The All Blacks take on England on November 4 before two Tests in France and one in Cardiff.