Are all the carriers' Galaxy S8 the same hardware and bands?

Are all the Samsung Galaxy S8s sold directly by the four national US carriers the same hardware supporting the same bands as each other and supporting both GSM and CDMA, but are just each locked to their respective carrier with bands unused by that carrier software disabled? Or is the actual underlying hardware different between the different US carriers versions of the S8?

If the hardware is the same, once the carrier-branded S8 is unlocked, can it be used on any US carrier?

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