Chris Sale had a weird season in 2016. On the bright side, he finished with career highs in games started (32) and innings pitched (226 2/3). However, the increased durability resulted in a lot fewer strikeouts and his rate stats fell drastically. After leading the league in K/9 in both 2014 (10.8) and 2015 (11.8) that number dropped to 9.3 last year. Often times a decrease in strikeouts, combined with a drop in velocity, could mean a pitcher is headed for a decline.
But that was not the case for the best pitcher in the American League. It turns out that Sale's strikeout numbers were actually down on purpose. It was part of a plan developed by Sale and White Sox pitching coach Don Cooper to allow the ace to pitch deeper into games by having easier innings. The thought process made sense - Sale was 27 at the time and had four seasons under his belt as a starting pitcher exerting maximum effort during every at bat. By making a conscious decision to pitch more to contact by pounding the strike zone he would be able to save some bullets for the playoffs.
The plan worked, and actually had an unintentional consequence that could help Sale have a career year in 2017. While Chicago wasn't able to reap the rewards in the playoffs the experiment gave him another method of attacking hitters. Throwing hard and striking batters out can only work for so long. Eventually a pitcher's velocity will decline and if they haven't learned other ways of pitching to batters then they are not going to have success into their 30s (think Tim Lincecum).
But so far in 2017 Sale is not there yet. His velocity is back and with it so are the strikeouts. In 21 2/3 innings this year he has struck out 29 while recording a 1.25 ERA. He has already complied two games of 10+ strikeouts, which represents half of his total from a year ago (when he did not record his first double digit strikeout game until the beginning of August).
This means we are witnessing prime Chris Sale right now. So far he has been able to both strike guys out and go deep into games. He has the stuff to get a K when he needs it, yet has also learned to pitch to contact if his pitch count is getting high. And sometimes even when he's "pitching to contact" he'll strike guys out because his stuff is that good. Chris Sale is not back to being his old self - he's the best version of himself we have ever seen.