Preheat to 350°F (175°C) and line baking sheets with parchment.
In a large bowl, cream softened butter with brown and granulated sugars until fluffy. Beat in eggs one at a time, then stir in vanilla.
In another bowl, whisk flour, baking soda, salt, and cinnamon, then fold into the wet mixture just until combined.
Stir in oats and pecans, then blend in warmed corn syrup until the dough is smooth.
Drop rounded tablespoons onto sheets, spacing 2 inches apart.
Bake 12–15 minutes, until edges are golden and centers set. Let cool 5 minutes on the pan before transferring to a rack.