Apple Inc. is facing an unprecedented challenge: persuading customers to buy its latest iPhones without their biggest new feature.

Apple is accelerating the rollout of a software update that will implant intelligence into its virtual assistant Siri and automate a variety of tedious tasks to coincide with the release of its latest iPhone.

Apple’s annual product launch Monday failed to immediately capture the hearts of investors, as shares of the world’s biggest company slumped during the event largely focusing on previously rolled-out artificial intelligence features coming to iPhones.