Tipping is recommended but not required. The Bhutan government do not require tourists to tip drivers, tour guides, waiters and other local people who will serve you, because their income is not bad. However, tipping is still recommended, because if you tip them, they will offer even better service, especially for hiking and mountaineering itineraries, you might need porters and cooks, and they need to carry heavy luggage or cooking utensils during the tour.
Some of our customers even tip their tour guides and drivers prior to the start of their tour.