What just happened? Elon Musk has threatened to sue Microsoft over his claim that the Redmond company illegally used Twitter data to train artificial intelligence models. Musk's tweet was a response to news that Microsoft is dropping Twitter from its advertising platform.

Mashable was first to report that as of April 25, advertisers will no longer be able to access their Twitter accounts via the Microsoft Digital Marketing Center's social media management tool. Moreover, users will no longer be able to schedule, create, or manage tweets or tweet drafts. They won't be able to view their past tweets and engagement on the platform, either.

Microsoft's decision comes after Twitter announced how much people will have to pay to use its new API; the company is keeping the free tier, but its functionality is severely limited. It's believed that the Enterprise level API has a starting cost of $42,000 per month, a price that has seen many smaller developers abandon their Twitter-based apps.

While Microsoft is one of the largest companies in the world, it seems Redmond isn't willing to hand over that much money at a time of belt-tightening that's seen it implement mass layoffs.

Not surprisingly, Musk is far from happy about Microsoft's move. In a tweet about the news, he replied, "They trained illegally using Twitter data. Lawsuit time."

While Musk didn't make it clear what he was referring to in the tweet, it's likely a reference to OpenAI using Twitter data to train its large language models powering the likes of ChatGPT. Microsoft doesn't own OpenAI, but it has made a multibillion-dollar investment in the company and is using its AI tech in products such as Bing and Edge – with great success.

In a separate tweet, Musk, who was one of the OpenAI co-founders before leaving the board in 2018, wrote that he was "open to ideas" about how to use Twitter's data but "ripping off the Twitter database, demonetizing it (removing ads) and then selling our data to others isn't a winning solution."

Whether Musk ends up suing Microsoft remains to be seen. The billionaire has a history of not following up on these sorts of things, such as when he threatened to sue Jack Sweeney, the creator of the @ElonJet account.

Microsoft has not commented on Musk's threat, and the Twitter press email account automatically replies to requests with a poop emoji.