From https://github.com/mapbox/mapbox-gl-js > Mapbox gl-js version 2.0 or higher (“Mapbox Web SDK”) must be used according to the Mapbox Terms of Service. This license allows developers with a current active Mapbox account to use and modify the Mapbox Web SDK. Developers may modify the Mapbox Web SDK code so long as the modifications do not change or interfere with marked portions of the code related to billing, acco…
The billing is pretty important. Using Mapbox GL JS 2.0 offline using a local tile server still requires an account and a per tile fee.
Per map load fee