Mix the smoked paprika, onion powder, garlic powder, thyme, rosemary, black pepper, ground mustard, ground cumin, brown sugar, and red pepper flakes in a small bowl.
Rub the spice mixture onto both sides of the ribeye steaks, making sure every inch is covered with the spice mixture.
Let the steaks sit at room temperature for about 30 minutes to absorb the flavors, if time permits.
Brush the grill grates with olive oil to prevent the steaks from sticking. Next, preheat the grill to high heat. Turn two knobs to high (450℉-500℉/230-260℃) and let the grill heat up for about 10-15 minutes.
Once the grill reaches the right temperature, place the steaks directly on the grill and cook for 3-4 minutes per side. Keep in mind that cooking times will vary depending on the thickness of the steak (and your preferred doneness). Then, lower the knob to medium (350℉-450℉/177-230℃) and finish cooking to your desired doneness.
Remove the steaks from the grill and let them rest for 5-10 minutes to allow the juices to redistribute. Top with garlic herb butter or slice the steaks against the grain and serve immediately.