Apple has apologised following revelations that it paid third-party workers to listen to voice recordings of Siri users.
The practice known as “grading” has been used by several tech firms as a way of improving the quality of speech recognition.
However, Apple, Google and Microsoft all halted such work recently, following public outcry.
Apple said it plans to resume grading – but only for Siri users who opt in.
The firm added that in the future only its own employees will be able to access recordings, not third-party workers at contracted firms.
Earlier this month, the company said it had halted grading following reports that workers had heard recordings containing intimate remarks made by Siri users.
Such recordings can be made accidentally, for example when the Siri app interprets another word or noise as the utterance “Hey Siri”, which is used to launch voice recognition.