Yes they are!
Why is that so hard for you to believe?
When the PS5 does come out, the PS4/XBox One will be 7 years old. Consoles typically have a 6-8 year lifecycle. The XBox One S and X, and the PS4 Pro were incremental updates to the product line. If you know anything about the history of consoles, you will know that every 2-3 years the console hardware is updated. This time, Sony and MS marketed the updated versions.
Typically when there was a hardware update in the past, the MSRP of the console was reduced. The 80gb Fat and 120gb Slim PS3 are good examples.
There is no guarantee that the PS5 will come out in 2020. There could end up being a production or development snag that could push the release date back to 2021. If everything stays on track then it will be released before the holiday season next year.
AMD which is the creator of the GPU/CPU Architecture that's used in the PS4 and XBox, created the Navi Graphics uARCH specifically for the PS5 and XBox consoles. It looks like AMD is doing well and I don't see them having any problems hitting their development targets. TSMC is the company that is subcontracted out to fabricate the chips that are used in the consoles. Since companies like Apple have 1st priority at TSMC and since TSMC is running at 100% capacity, they might have a difficult time fulfilling these new orders for the new console Processing units.
The new consoles will use a new CPU architecture as well. Quite honestly the Bulldozer CPU architecture that's being used in all versions of the Xbox One and PS4 is and was quite weak. Zen 2 is miles ahead of the Bulldozer. Since Flash memory has become much, much cheaper, I expect the new consoles to use Solid State drives.
Since the PS5 is using x86-64 CPU architecture, there is NO reason for it to NOT be backward compatible with the PS4. However, given the history of these companies, they might manufacturer an excuse for No backward compatibility.
I really don't see the selling point of this new console. I think the only way Sony and MS could justify the next gen is to have developers make games that are so graphically demanding that the game would be unplayable on the PS4 and XBox One.