Apple Inc. is planning to pay about $1 billion a year for an ultrapowerful 1.2 trillion parameter artificial intelligence model developed by Alphabet Inc.’s Google that would help run its long-promised overhaul of the Siri voice assistant, according to people with knowledge of the matter.

Following an extensive evaluation period, the two companies are now finalizing an agreement that would give Apple access to Google’s technology, according to the people, who asked not to be identified because the deliberations are private.