AMD may want to be concerned. Based on alleged Time Spy benchmark results shared by hardware leaker @_rogame, the AMD Ryzen 9 3900X will have a strong rival in the upcoming Intel Core i9-10900KF.
The i9-10900KF is one of Intel's forthcoming Comet Lake desktop chips and will compete with AMD's recently launched Ryzen 3000-series (codename Matisse) CPUs. More specifically, the i9-10900KF will be trading blows with the Ryzen 9 3900X, which makes today's fight so interesting.
As a quick summary, the i9-10900KF is on Intel's 14nm node and will feature 10 cores, 20 threads and 20MB of L3 cache. The chip reportedly has a 3.7 GHz base clock and, thanks to Intel's Thermal Velocity Boost (TVB) feature, boost to 5.3 GHz. As dictated by the "F" suffix, the i9-10900KF is part of the breed of Comet Lake CPUs that lack integrated graphics.
On the other side of the octagon, the Ryzen 9 3900X debuted on TSMC's 7nm FinFET manufacturing process and comes flexing 12 cores, 24, threads and 64MB of L3 cache. The processor clocks in with a 3.8 GHz base clock and 4.6 GHz boost clock. On paper, the i9-10900KF is already at a disadvantage with two fewer cores and significantly less L3 cache. However, it does flex higher clock speeds.
According to the Time Spy entry, the i9-10900KF had a 12,412 CPU score. The Ryzen 9 3900X, in return, scored 12,857 points. Therefore, AMD's chip is only up to 3.6% faster. In the i9-10900KF's defense, it was paired with DDR4-2400 RAM, while the Ryzen 9 3900X's system was on speedier DDR4-3200 memory.
Indeed, memory speed shows a significant impact on the Time Spy benchmark. The same Ryzen 9 3900X scored 13,913 and 13,650 points with DDR4-3600 and DDR4-3800 memory, respectively.
Meanwhile, the i9-10900K, which is essentially the i9-10900KF but with an iGPU, scored 13,142 points with DDR4-2666 memory. Since the i9-10900KF is basically a replica of the i9-10900K but without integrated graphics the performance for both processors should be in the same neighborhood.
If we compare the i9-10900K DDR4-2666 result to the Ryzen 9 3900X DDR4-3200 result, Intel's processor is actually up to 2.2% faster. That's the problem with leaked benchmarks. You can never be sure of the conditions of the test system or operating system. When unreleased hardware is involved, there's always a strong chance of discrepancy between the results. Plus, this has no implications as to whether the i9-10900KF can keep up with the Ryzen 9 3900X in other real-world scenarios, especially multi-threaded ones.