In a head-turning interview, $Microsoft (MSFT.US)$ CEO Satya Nadella called voice assistants, including $Apple (AAPL.US)$'s Siri, $Amazon (AMZN.US)$'s  Alexa, and Microsoft's own Cortana "dumb as a rock."

Earlier this month, Nadella revealed in an interview with the Financial Times that none of the voice assistants really work.

We had a product that was supposed to be the new front-end to a lot of information that didn't work," he said.

In 2016, Nadella had boasted about the voice assistants, claiming that "bots are the new apps." But as artificial intelligence continues to emerge, he has since changed his opinion.

Microsoft launched its voice assistant service Cortana in 2014. Two years ago, Nadella discontinued its service on Android and iOS, explaining that he no longer saw the product as a competitor to Alexa or Google Assistant, The Verge reported.

Now with a focus on AI, Microsoft recently invested about $10 billion in OpenAI, the research laboratory behind the AI chatbot ChatGPT.

Microsoft also launched its new Bing search engine, created in collaboration with OpenAI. The search engine now displays ChatGPT-like skills, including writing personalized emails, translating texts in over a hundred languages and recommending various searches.

Adam Cheyer, co-creator of Siri, told the Financial Times that ChatGPT's ability to understand complex instructions has left existing voice assistants in the dust.

The previous capabilities have just been too awkward," he said. "No one knows what they can do or can't do. They don't know what they can say or can't say."