In a large bowl, whisk together the pumpkin puree, instant vanilla pudding mix, and cold milk for about two minutes until the mixture thickens slightly.
Gently fold in the thawed whipped topping using a spatula until just combined. Do not overmix.
Stir in the pumpkin pie spice.
Chill the pumpkin fluff for at least 30 minutes before serving to allow it to set completely.
Serve cold with graham crackers, apple slices, or gingersnaps for dipping.
Notes
For a pie version, press a graham cracker crust into a pie plate before folding in the whipped topping, then chill.
If you prefer a lighter version, use sugar-free pudding mix and light whipped topping.
You can substitute the vanilla pudding with cheesecake flavored instant pudding for a different flavor profile.