How long is a new Apple TV actually supposed to last?
The honest answer is that nobody really knows, and that uncertainty is the whole story. Apple's track record with the Apple TV line is genuinely good, the third-gen model from 2015 still gets updates, which is remarkable for consumer electronics. But the company has also killed the product twice, and the current Apple TV 4K exists in a weird middle space where it's clearly not a priority compared to the iPhone or Mac.
What I'd want to know is whether the newest hardware has enough headroom for the next wave of streaming demands. AV1 decoding, higher bitrate HDR, and the slow creep of app bloat will eventually strain even well-supported boxes. Software support matters, but silicon limits matter more, and Apple tends to stay quiet about those until a product is quietly dropped from the lineup.
I'd put my money on three to five years of solid updates, then a long tail of security patches. That's better than most rivals, but it's still a gamble if you're buying today and expecting a decade of service.