Whisk the flour, cinnamon, baking soda, and salt together in a medium bowl. Set aside.
In a stand mixer fitted with a paddle attachment, beat the butter, brown sugar, and granulated sugar together on medium-high speed until combined and creamy, about 2 minutes.
Add the eggs, molasses, and vanilla and beat on high speed until combined, about 1 minute.
Scrape down the sides and the bottom of the bowl and beat again as needed to combine.
Add the dry ingredients to the wet ingredients and mix on low until combined.
With the mixer running on low speed, beat in the oats and butterscotch morsels. The dough will be thick and sticky.
Cover and chill the dough for at least 45 minutes in the refrigerator (and up to 4 days). If chilling for longer than a few hours, allow to sit at room temperature for at least 30 minutes before rolling and baking because the dough will be quite hard.