"This could change everything" Engineers in Japan just shattered the world record for the fastest internet speed, achieving a data transmission rate of 319 Terabits per second (Tb/s), according to a paper presented at the International Conference on Optical Fiber Communications in June. The new record was made on a line of fibers more than 1,864 miles (3,000 km) long. And, crucially, it is compatible with modern-day cable infrastructure.