Do I need a Verizon HTC One M9 to use Verizon's network?

I'm currently on a Verizon HTC One M7 and due for am upgrade. Rather than doing the two year subsidized contract, however, I am considering buying an unlocked version of the phone on Swappa for 0 or so and then just bringing that phone to Verizon.

Is this possible? Back in the day I recall that wouldn't work because Sprint and Verizon used CDMA bands while the rest used GSM with Sim cards and the like, but I thought I remember reading that it's no longer a problem on Verizon.

So can I buy an unlocked M9 and bring it over or does it have to be a Verizon specific model to work?

Thanks in advance.

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