"I have heard of some things about the All Blacks that could be quite explosive if they were made public, and if it does get dirty, then I will raise a couple of those things. At the moment, I'm just keeping my counsel," Gatland wrote.
Don't count on Hansen kicking things off again - not unless provoked. At this stage, he appears unlikely to bite first.
Speaking to the Herald on Sunday in Edinburgh, for now Hansen is keen to move on and also distance the Welsh test in Cardiff, the last of the All Blacks' northern tour, from the drawn Lions series.
"The Lions is a team made up of four countries and the best of those players from that region," Hansen said. "Wales is just one of those teams. Are their similarities with the coaching? Yes, of course, but it's a totally different competition."
Like many Kiwis, from the late Jerry Collins to Justin Marshall, Hansen has strong links with Wales, having coached the national team before joining Sir Graham Henry and Wayne Smith with the All Blacks.
"I have an affinity, of course. There was a lot of hard work that went into building a foundation that they could grow upon over the years. I've got some good mates there still. Some of the times I had there with the players and management were the best times I've had in rugby. I keep in touch with a lot of them and I look forward to any contest with Wales."
Given that, and the frequent verbal barbs traded during the Lions series, one would naturally assume this week to be more personal than most; to have a bit more edge or added spice for the men at the helm. Not so, says Hansen.
"I always laugh when people say is it more personal to you. It's not personal. Rugby is a team game. Once you make it personal, you tend to drop the ball."
While the All Blacks don't have a set of rules per se, they do have non-negotiables. Top of that tree is team first, individual second.
"If I'm expecting that from the players, I've got to live those standards myself. It has never been personal. It never will while I've been a coach. For me, coaching is about creating an environment where you can help young men who are motivated and talented to express and improve themselves. Winning is just a by-product of all of that."
In a results-driven industry, it would appear Hansen did not enjoy a happy time in Wales. Following on from Henry, from 2002 to 2004 Hansen won 10 from 30, a stretch which included 11 successive losses and its share of frustrations.
Looking back on that turbulent time, many credit him with instilling a professional culture and laying the platform for Wales' 2005 Grand Slam. But there's no doubt this was a challenging period for the now world-leading coach.
"If you look at what we had to do, yeah, it was tough, and yeah, being a foreigner trying to get change is difficult because not everyone wants to come with you. But from within the team, we had a group of young athletes who wanted to change and be better. Over a period of time, we got there. Some of those athletes we started with went on to have great careers for Wales. I look back with a sense of pride about that because we helped start them on their way."
Former Welsh centre Tom Shanklin, who played 70 matches, told the Telegraph this year Wales were fitter, eating better and had specific training plans by the time Hansen departed.
"When he left, Wales were in a far better position," Shanklin said. "He gave us the freedom to play."
Gatland's record (50 per cent from 118 matches) isn't drastically better. Against the three Southern Hemisphere superpowers he is 3/36, and 0/10 when facing the All Blacks. In that time, the All Blacks have averaged a 20-point winning margin.
For what it's worth, Hansen is not a numbers man. He can't tell you how many games he has won as All Blacks coach (71/80 at 87.5 per cent) let alone recall the figures from his Welsh tenure.
"If you're good enough, you win, as long as you do the work. If you do the work and you don't win, then you're not good enough. We worked hard and eventually we started to win a few games but we went through a period where we didn't win too many.
"That was just a reality. It's an inconvenient fact that when you let your stocks get that low, you have to make changes, and that's what we did while we were there."
Traditionally, the last match of the season is the hardest for the All Blacks. The end is near; thoughts can drift to kicking off the boots and soaking up some summer sun.
Wales should be reasonably well placed after resting several leading players this weekend against Georgia, but the All Blacks have done that all season. Personal or not, Hansen will be intent on signing off this season on a memorable note.
