Hong Kong

IT is one of the best-guarded borders in the world, and one of the most time-consuming to cross. Yet in the past few months, a new agreement has let people speed over it billions of times.

The border is the digital one that divides China from the rest of the world. It is laden with inefficiencies and a series of filters known as the Great Firewall, which slows Internet traffic to a crawl as it travels into and out of China. Now, a partnership between a US startup and a Chinese Internet behemoth has created a sort of fast lane to speed traffic across the border. In the process, the two companies are establishing a novel business model with implications for other US technology firms looking to do business in China's politically sensitive tech industry.