Prep the slow cooker: Lightly grease the insert or use a liner to make cleanup easier.
Mix the sauce: In a bowl, combine BBQ sauce, broth, apple cider vinegar, brown sugar or honey, smoked paprika, garlic powder, onion powder, chili powder, salt, pepper, and Worcestershire. Stir until smooth.
Arrange the chicken: Place chicken thighs in the slow cooker in an even layer. It’s fine if they overlap slightly.
Pour and coat: Pour the sauce over the chicken, turning the pieces once to coat.
Nestle them back into the sauce.
Cook low and slow: Cover and cook on LOW for 4–6 hours or HIGH for 2.5–3.5 hours, until the chicken is very tender and reaches 165°F/74°C internally.
Optional shred: For pulled-style chicken, transfer thighs to a plate and shred with two forks. Return the meat to the cooker and toss with the sauce. If you prefer whole pieces, leave them intact and spoon sauce over the top.
Finish the sauce: If you want a thicker glaze, remove the lid and cook on HIGH for 15–20 minutes to reduce.
Stir in the butter at the end for shine and a silky finish.
Serve: Spoon over rice or mashed potatoes, pile on toasted buns for sandwiches, or pair with slaw and cornbread. Garnish if you like.