Apple has agreed to buy Pullstring, a San Francisco-based startup that enables the design and publishing of voice apps, Axios has learned from multiple sources.Why it matters: This could help Siri better compete with Alexa.Background: Pullstring was founded in 2011 by a group of former Pixar executives, and originally was used to power interactive voice apps for toys (including Hello Barbie in 2015). It later broadened its approach with the introduction of such IoT products as Amazon Echo and Google Assistant. It raised around $44 million in venture capital, from firms like CRV, Greylock, True Ventures, Khosla Ventures and First Round Capital. According to PitchBook, its most recent post-money valuation was just north of $160 million.The upfront deal value is said to be around $30 million, plus around $10 million in potential earn-outs for management. That would include CEO Oren Jacob, who once served as Pixar's CTO.Voice is seen as one of the next big things and Apple has been way behind both Google and Amazon in terms of adoption and being open to developers. Making it easier to write voice apps combined with a more open Siri could help close the gap, even though both Google and Amazon continue to invest heavily in voice. Apple was not immediately available for comment.