XL tyres are reinforced tyres designed for heavier vehicles, which explains the meaning of the abbreviation "extra load".They are usually used by SUVs, large sedans, vans and electric cars. The reinforcement makes the tyre perform better under heavy loads.Whether it is an XL tyre is not directly dependent on the weight index, although most XL tyres have a weight index above 90 (>600 kg).
Michelin Pilot Sport 4 SUV is made in 118 sizes, which of them 9 are made in the XL specification :