The Ultra 4850 (2024) has some improvements over the 4800 (2020). It has a bit faster processor, so it's a bit more "snappy". It supports WiFi 6 (802.11ax) but not the 6 GHz radio band. Compared to my 4800 it is a faster WiFi connection, but that really doesn't matter as no content available online comes close to maxing out the wired connection, let alone a wireless one. The 4850 also has the latest HDMI 2.1b standard, compared to the 2.0b standard on the older one. But again, there's no need for that with any existing media stream. It comes with the new rechargeable remote, but you can also just buy the same remote and use it with your 4800. There's one other techno-geek feature that the new one has, and that's called QMS. But you need a TV that supports QMS for it to mean anything to you, and it's so new that there aren't a lot of TVs that support it.
So the only significant upgrades are the faster processor (some haven't even noticed the faster speed, but it is there) and the latest WiFi protocol. Only you can decide if that's enough to justify replacing a working device.
Dan
Roku Community Streaming Expert
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