X owner Musk has threatened Apple with legal action after claiming it had made it "impossible" for apps to compete with ChatGPT-maker OpenAI in the store. He also called OpenAI boss Sam Altman a "liar" - after Altman claimed Musk used his platform to "benefit himself and his own companies".

The row is the latest flashpoint in what is an ongoing feud between the billionaires who co-founded OpenAI - but now fiercely compete after Musk left the firm. Apple announced a partnership with ChatGPT in June 2024 - but there is no suggestion Apple favours one app over the other, and several rival AI apps such as DeepSeek and Perplexity have topped the App Store charts since then.

In a statement sent to the BBC, Apple said: "We feature thousands of apps through charts, algorithmic recommendations and curated lists selected by experts using objective criteria." In a later post Musk took aim at Apple again, asking the firm why it would not promote X - or its AI app Grok - in the "Must Have" section of the App Store. "X is the #1 news app in the world and Grok is #5 among all apps," he said in a post now pinned to his X profile.

ChatGPT is currently the most downloaded free app in the UK, with Grok a close third. X does not make the top 40. This seemed to draw the attention of Altman, who linked to a report by tech newsletter Platformer which claimed Musk had made his own personal X posts more prominent in people's feeds. The feud between Musk and Altman has, over time, encompassed a slew of lawsuits, email dumps and social media digs.

Their rivalry can be traced back a decade, with Musk's now public belief that OpenAI, under Altman's leadership, abandoned the principles he and others used to found it in 2015. The firm was created with the intention of building artificial general intelligence (AGI) - AI that can perform any task that a human being is capable of - but by making its technology open-source and promising to "benefit humanity". (BBC/ Getty Images)