Cook said that so-called "native" apps will be coming for the Watch and was the biggest news in the early part of his address at an annual developers conference, but the company was expected to later announce details of a widely anticipated streaming music service.
The company also unveiled new details about its Apple Pay service, saying it was already supported by more than 2,500 banks and will surpass 1 million locations accepting it next month. In addition, the company said it would roll out the service to the United Kingdom next month.
In a related move, Apple said it would rename Passbook, its app for credit and debit cards and boarding passes, to Wallet.
Apple Inc shares were down about 1 percent at $127.48 in early afternoon trading as Cook and others spoke.
The company also unveiled the next version of its operating system for Macs, El Capitan, continuing the company's theme of naming key updates to the software after California landmarks. The software will be available in the fall.
Like other Apple products, the Watch's commercial success will likely hinge on a compelling collection of apps. But early apps for the timepiece have been tethered to the iPhone, placing some limits on what developers could do.