Each manufacturing company has its own recipes for Montreal steak seasoning. If their recipe is gluten-free, it will say so on the label.  If a commercial seasoning mix is not explicitly labeled gluten-free, you cannot assume it is. Don’t guess, even if you do not see wheat, rye, barley, and oats on the ingredient list.   However, if you use this Montreal steak seasoning recipe, you can be sure it is gluten-free. The only ingredients are whole spices, dried herbs, and salt.