Preheat your oven to 450°F (232°C).

In a mixing bowl, combine the crushed pecans, smoked chili powder, garlic powder, onion powder, salt, and black pepper. Mix well to create the spice rub.

Pat the prime rib roast dry with paper towels. Rub the olive oil all over the roast, ensuring it is well-coated.

Generously apply the pecan and chili spice mixture all over the roast, pressing it into the meat to adhere.

Place the seasoned prime rib on a roasting rack in a large roasting pan. Insert a meat thermometer into the thickest part of the roast, avoiding the bone.

Roast the prime rib in the preheated oven for 15 minutes. Then, reduce the oven temperature to 325°F (163°C) and continue roasting until the internal temperature reaches your desired doneness (about 120°F for rare, 130°F for medium-rare, or 140°F for medium). This may take approximately 1.5 to 2 hours.

While the prime rib is roasting, prepare the gravy. In a large skillet over medium heat, melt the butter. Add the sliced onions and cook, stirring frequently, until they are deeply caramelized, about 20-25 minutes.

Once the onions are caramelized, add the beef broth and Worcestershire sauce to the skillet. Bring to a simmer and let it reduce for about 10 minutes, stirring occasionally. Season with salt and pepper to taste.

Once the prime rib is done, remove it from the oven and let it rest for at least 20 minutes before slicing. This allows the juices to redistribute.

Serve the sliced prime rib with the velvety caramelized onion gravy drizzled over the top. Garnish with fresh thyme sprigs if desired.