Apple appeared to leak the shipping date of its latestduring a launch event for other products in San Francisco on Wednesday.
Craig Federighi, Apple's senior vice president of software engineering, was on stage showing off new features of the iPhone 6S smartphone. During the demonstration, he opened a personal email from Phil Schiller, Apple's senior vice president of marketing, with the subject line "El Capitan status."
"El Capitan is looking great and the feedback from the beta has been fantastic," Schiller wrote in the email. "El Capitan ship date is September 30."
The email was marked as confidential. It's unclear whether Apple was just being cheeky or whether it unintentionally showed the release date.
Shortly afterward, the company's website announced that the software is "coming September 30." Apple is known for keeping product launches secret, which typically creates an air of mystery and leads to a fast-and-furious rumor mill.
Apple didn't immediately respond to request for comment.
El Capitan is the upcoming version of Apple's Mac software, which has been available in public beta since July. It's expected to refine and streamline the features in Apple's current Yosemite software. The company says El Capitan should make common actions easier for users. For example, people will be able to view two open windows at once with a Split view screen.
The revelation came during Apple's annual iPhone event. In addition to the new iPhone 6S and iPhone 6S Plus, Apple debuted a new Apple TV streaming-media box and a larger, more work-friendly.
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