To keep that claim in perspective (quoted from Arstechnica article
https://arstechnica.com/science/2019/10/inside-googles-quantum-computing-efforts/2/):
"Google's argument for quantum supremacy focused on the claim that a simulation of its processor's behavior would take 10,000 years on a state-of-the-art supercomputer. But IBM noted that Google's argument was based in part on memory starvation, and supercomputers have hard disks that can hold temporary data during the computations. If that disk space is factored in, IBM argues, the calculation could take as little as 2.5 days. At a couple of minutes, the quantum processor beats that handily, but there's still the chance that algorithm optimizations will cut the margin considerably."
"This is somewhat similar to the experience D-Wave had, where every indication of a quantum advantage was quickly matched by computer scientists returning to the classical computing algorithms and finding ways of extracting speedups. And Google, to an extent, has expected this. Neven told us that the company had already funded "red team" researchers in academia to try to do similar optimizations."
"This is sort of a misdirection. Google will undoubtedly be able to add additional qubits, which will cause the classical simulation to slow down further. At the same time, this reaction does suggest that the existing players in the field are starting to get sensitive to competition—even if said competition doesn't even have a marketable product yet."
