Apple has acquired a San Francisco-based voice app startup PullString in an effort to bolster its smart assistant as voice takes over.

The startup was last valued at $US163.57 million, according to PitchBook, but the terms of the deal were not specified in the original report from Axios.

Pullstring was founded in 2011 by former Pixar employees — CEO Oren Jacob is Pixar’s former CTO —  and originally developed voice systems for popular toys, like Mattell’s talking Hello Barbie doll back when the company was called ToyTalk.

Today, it helps build and develop skills and apps for Amazon’s Alexa and Google Assistant.

It’s believed that Apple is acquiring PullString in an effort to close the gap between its own voice-assistant, Siri, and Amazon’s Alexa and the Google Assistant.