Williams, if he's fit, is expected to come into the squad possibly in time for the clash at the Cake Tin, but more probably the Argentina test in Hamilton on September 10.
Other potential All Blacks such as Ardie Savea and Akira Ioane, who are expected to also be at the Olympics, are unlikely to be considered for the XV-man game until the end-of-year tour when 36 players will be taken for two tests against Ireland and one each against Italy and France.
Williams, though, has a proven ability to switch between codes in quick order and is renowned for keeping in supreme physical condition. In 2014, he played for the Roosters in the NRL semifinal on September 27 and then a test for the All Blacks against the US on November 2.
The All Blacks have faith in Williams' ability to make a fast transition from sevens to XVs and their decision to elevate the 30-year-old to the leadership group is indicative of that confidence.
Williams' desire to be in the leadership group is also a sign of his desire to establish himself in the No 12 jersey.
He has won 33 test caps since his debut in 2010, but his decision to return to the NRL in 2013 and 2014 and the relentless form of Ma'a Nonu prevented him from becoming a regular test starter.
With Nonu now at Toulon, the way has been cleared for Williams to become an integral senior All Black both on and off the field. His form at the World Cup was outstanding and, although he played mostly off the bench, his contribution was significant.
He transformed the opening game against Argentina when he arrived with 35 minutes remaining and also had a major impact in the final, with his first touch being an outrageous offload to Nonu that led to a try.
No one in New Zealand Rugby is taking anything for granted but, despite having options to play rugby in Europe and league in Australia, there is rising optimism that Williams' preference is to stay where he is beyond this year.
Playing against the British Lions next year is an obvious goal, as is winning 50 test caps, and New Zealand Rugby would ideally like to have an extension sewn up before the All Blacks head to Chicago to play Ireland in October.