There is no guarantee for that length of support, or what "support" means.
Does "support" mean the Apple OSX 2024 will install on it? Will it be patched and updated?
What Apple has typically done, and what contractually they must do, are two different things.
(If Apple has made a statement about end-of-support support for the 6,1, please correct me.)
Obtaining service for your Apple product after an expired warranty - Apple Support
Learn about your options for getting service and parts for Apple devices that are past their warranty period.
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There are actually laws but they change based on the country. No, there is no guarantee that Apple will support the hardware in the latest OS, and the 2013 Mac Pro is unique (I believe), for never having *any* hardware updates over the six years it was manufactured. However, Apple will not consider the computer obsolete until the end of 2024 and supply parts longer than that. If they stop supporting the hardware with patches and updates before the end of 2023 it would also be a first.
The 2009-2012 Mac Pro was only officially dropped in Catalina, seven years after it was last manufactured. Even then it works with minor tweaks. Given that the 2013 Mac Pro supports Metal 2 out-of-the-box, I don't see why it won't run the latest OS but be slowly excluded from headline features—as already happened with Side Car. Of course, if Apple switches completely to ARM, then all bets are off but that applies to most/all Intel Macs.
So if you choose to stick to an alarmist/cynical viewpoint, then that's your choice but the evidence doesn't support it.