603 for maglevs, 574.8 for steel rail, set in France in 2007 by a hotted up, modified TGV.
China holds the record for a stock train at 487, set in 2010.
(all per Wikipedia)
It looks like the article might be implying that they will be the fastest trains operating in revenue service when they enter service, but that surely needs to be demonstrated with a production train in revenue service.
...production train in revenue service over the period of usual track maintenance. It's not the rails I'm worried about but the overhead lines, have a look at the TGV record run there's a lot of arcing that can't be good for them. On the pantograph side the contacts are carbon, notoriously brittle, and generally speaking over 300km/h things become dicey just because of heat buildup. Automated retraction systems can prevent the worst, meaning the pantograph getting tangled in the lines at speed, but, well: Production revenue service. Can't have those fail-safes kick in or you'll mess up the timetable.
European high speed trains actually got slower vmax over the years for the simple reason that the rest of the systems is reaching practical limits and it doesn't make sense to have trains that can drive speeds that the track will never reasonably support. If you want to go faster you want to go contactless which means building a whole new, incompatible, network. And the only maglev system with affordable tracks, as in bucks per kilometre (TSB), has a design limit of ~200km/h: It uses bog-standard third-rail like technology for electrification, everything else would be expensive. But for its intended use-case as an S-Bahn 200km/h are plenty and you get nice bonuses such as 10% gradients and inexpensive viaducts (because no point-loads they can be built way lighter).
China, in the end, isn't that large. You can do high-speed sleeper trains, 12-14h or such, from one end of the country to another with existing stock technology, and so btw could the US.
If it has an operating speed of 450km/h this would be impressive.
But just reaching this speed is far from a world record, the French TGV record from 1990 is 513km/h, it reached 574.8km/h in 2007 which is the current world record.
The US is set to unveil their high speed competitor soon with a train called the "American Superior." It is stated to have a top speed of 80km/h and will launch on a single 10km track by the year 2083.
As someone who frequently uses Japan's bullet trains, that max speed is cool, but also of limited value since trains tend to stop in places. There are some areas, moreso in china that Japan, where that might make sense, but even if your train doesn't stop at all stations, you're still behind the ones that do until a track split to allow passing.
Isn't scheduling able to mitigate issues like that? It helps a lot that Shinkansens are pretty much always on time. Can't wait for the Chuo to open eventually though.
You've already got various services running on the same lines basically as close together as they can, so there's only so much wiggle room to accomdate something faster than all of them longer stops on existing services could do something, but that has other knock-on effects. Building a new rail and retrofitting every station would work, but it's also a nightmare to both get the land and do all that development.