There are four compounds; Hard, Medium, Soft and Super-soft. Each race, Bridgestone will bring two compounds. Each team must use both compounds during the race, so at some point the each car will be on a less-than-perfect compound. This could make tactics more interesting, with two long stints and one short one. The tyres will be visibly marked so everyone will know which compound is being used at the time.
Tyres generally will be harder, and so slower. There’ll be less grip, so more driver skill required.