The biggest WatchOS 27 upgrade could finally make Siri useful on the wrist.

For one of his final major public moments as Apple’s CEO, Tim Cook may give Wall Street something it’s long been waiting for: answers about the company’s artificial intelligence strategy.

The new “Siri AI,” as it is now being called, is what Siri should have been from the very beginning: an AI assistant that is more conversational, draws on personal context, and can complete actions on...