This fall, Apple will make some of its flagship iPhones outside China for the first time, a small but significant change for a company that has built one of the most sophisticated supply chains in the world with the help of the Chinese authorities. But the development of the iPhone 14, which is expected to be unveiled on Wednesday, shows how complicated it will be for Apple to truly untangle itself from China.

More than ever, Apple’s Chinese employees and suppliers contributed complex work and sophisticated components for the 15th year of its marquee device, including aspects of manufacturing design, speakers and batteries, according to four people familiar with the new operations and analysts. As a result, the iPhone has gone from being a product that is designed in California and made in China to one that is a creation of both countries.

The critical work provided by China reflects the country’s advancements over the past decade and a new level of involvement for Chinese engineers in the development of iPhones. After the country lured companies to its factories with legions of low-priced workers and unrivaled production capacity, its engineers and suppliers have moved up the supply chain to claim a bigger slice of the money that U.S. companies spend to create high-tech gadgets.