I can't tell you what you'll find inside a new Mac - Apple multi-sources when practical. I have a Late 2013 27" iMac with 3TB Fusion. System Report lists the spinner as an "Apple ST3000DM001," however, ST3000DM001 is a Seagate part number, and that particular model number has some "history."
Anyone wondering why the OP is concerned need only look at this:
https://www.backblaze.com/blog/3tb-hard-drive-failure Further, it's the same drive covered by Apple's 27" iMac 3TB replacement program.
However, we have to remember that these were drives manufactured in 2011 (both those reported on in the Backblaze article, and those involved in Apple's replacement program). Clearly, there
was a problem. That does not necessarily mean there is a problem with that model when manufactured in subsequent years (as they say on Wall Street, past performance is not predictive of future results).
Considering matters like warranty costs and company reputation, one hopes that Seagate has addressed the cause(s) of those failures. Other drives they make show reliability rates far closer to industry norms. It would also be against Apple's best interests to continue to source that model if there was reason to believe Seagate had not addressed the problem (Apple does expect to make a profit when it sells those 3-year AppleCare contracts). But those are hopes and suppositions on my part.