OpenAI's annualised revenue is about $20 billion less than previously signalled, the Financial Times reported, citing financial documents shared with investors.

The ChatGPT maker recently told investors its annualised revenue was approaching $50 billion at the end of September, far short of the $70 billion figure reported by media late last month. OpenAI declined to comment.

The gap arose from attempts by OpenAI's own investors to draw a direct comparison with rival Anthropic. The two calculate revenue differently: Anthropic includes sales made through cloud partners such as AWS and Google Cloud, while OpenAI counts only net revenue.

The report rattled markets on Thursday. The Nasdaq sank 1.25 per cent, its worst day since mid-August, and the S&P 500 fell 0.5 per cent. Nvidia dropped 2.9 per cent, Intel 5.3 per cent and Oracle 5.5 per cent.

The episode highlights investor anxiety over whether AI demand can justify the industry's enormous infrastructure spending. Both OpenAI and Anthropic are reportedly preparing for public listings.