AMD unveiled its Ryzen 4000 series processors at CES 2020, with the Ryzen 3 4300U, Ryzen 5 4500U, Ryzen 5 4600U, Ryzen 7 4700U and Ryzen 7 4800U all confirmed to be arriving in various laptops later this year. All are Zen 2 chips has based on TSMC's 7 nm process, much like the Ryzen 9 3900X is that we reviewed last year. However, while there have been rumours of a Ryzen 9 4900H, AMD has not unveiled a corresponding Ryzen 9 SKU for its 4000U series.
Except, Lenovo may well have just done so. Posted yesterday on YouTube, which has since been taken down, a datasheet for the Yoga Slim 7 (14" AMD) lists it supporting up to a Ryzen 9 4900U processor. Seemingly recorded at CES 2020, a similar datasheet circulated at the time of the conference merely listed the device as having up to an "AMD Ryzen 4000 series (TBA)" processor.
On the one hand, this could simply be a misprint that inadvertently made its way to the show floor at CES. The fact that Lenovo circulated a different datasheet would suggest so. On the other hand, Lenovo describes the Yoga Slim 7 (14" AMD) as supporting "up to AMD Ryzen 9" processors on the device's product listing.
A few months ago, reference to an "AMD Ryzen 9 Pro B12 (15W)" was spotted among a list of Renoir APUs too. While the above does not prove that a Ryzen 9 4000U series chip, or specifically the 4900U, is in the works, we would not dismiss out of hand that such a SKU exists. Given the discrepancies between Lenovo's two datasheets and the fact that no other OEM has mentioned the existence of the Ryzen 9 4900U, AMD could have shelved it for the time being.
If the Ryzen 9 4900U is on its way to market, then do not expect it to go beyond the eight cores and sixteen threads that the Ryzen 7 4800U already offers. Even the 4000H series does not go beyond this threshold, so we doubt a Ryzen 9 U SKU would either. In short, besides a clock speed boost, we struggle to see what a Ryzen 9 4900U could offer over the Ryzen 7 4800U besides a modest clock speed boost. Perhaps, that is why we have heard nothing concrete about it.