In 2017, Breitling and Tudor announced a partnership which meant that Tudor would use the Breitling B01 caliber for its Heritage Black Bay chronograph that they released the same year.
Essentially, this deal is an exchange between the two brands, since Breitling gets to use Tudor’s in-house caliber MT5612 movement to power its Superocean Heritage II. Breitling has, in turn, renamed it the B20 after its modifications. Tudor’s modifications to the B01 caliber include a tungsten winding rotor, variable inertia balance wheel, silicon balance spring, and the axis. (za https://millenarywatches.com/breitling-caliber-b01/)