China has so many high-speed trains, it's running out of numbers. So it's adding an "X" series for the fastest ones. 

China State Railway Group (China Railway) announced the change on Friday. The X-series will be used for trains that run above 350 km/h. The change will be rolled out in two batches, in late November and late December. Services will keep running to the current timetable.

China's newest high-speed train, the Fuxing CR450 electric multiple unit (EMU), has passed all type tests as of March 2026, said Zhao Hongwei, chief researcher at the China Academy of Railway Sciences Corporation Limited (CARS). It reaches 450 km/h in testing and 400 km/h in service, making it the world's fastest high-speed train in operation.

And it does that without using much more power. Zhao said the CR450 uses less than 22 kWh per kilometer at 400 km/h, while CARS data shows 350 km/h trains use 19.5 to 23.5 kWh per kilometer.

Under China Railway's numbering system, prefix letters indicate a train's speed category or service type. The X-series will cover trains above 350 km/h. The G, T and K series will denote trains with maximum operating speeds of 350 km/h, 300 km/h and 200-250 km/h.

China's rail network has kept expanding, and so has the number of services. From 2014 to 2025, the number of 300-350 km/h train sets rose by 209%, from 1,018 to 3,149 standard sets. Some number series are now running out of available numbers – the main problem the adjustment addresses.

According to a railway science and technology innovation plan for the 15th Five-Year Plan period (2026-2030), issued on Monday, China will develop at least 20 typical application scenarios or demonstration projects, including for the 400 km/h high-speed train system.