OpenAI's revenue is growing, but the company's latest figures put it well below the $70 billion annual pace reported last month.

The ChatGPT maker told investors it was nearing a $50 billion annual revenue rate at the end of September, according to a Thursday Financial Times report, which cited financial documents shared with investors.

The difference comes down to how revenue was counted. According to the FT, investors tried to put OpenAI and rival Anthropic on similar footing when comparing sales.

Anthropic includes sales through cloud partners like Amazon Web Services and Google Cloud in its revenue figure, while OpenAI leaves those sales out. Investors tried to adjust for that difference, leading to the higher reported $70 billion number that was spread last month.

An annual revenue pace is essentially an estimate of how much a company would earn over a year given sales stay at their current level.

OpenAI Quarterly Revenue

OpenAI Quarterly Revenue

SOURCE: The Latent

These discrepancies make it harder for investors to compare OpenAI and Anthropic, as they weigh whether AI sales can justify the companies' massive spending on compute infrastructure. Those questions could also soon matter to retail investors as Anthropic prepares for an IPO later this year. OpenAI has ruled out a 2026 listing, citing AI safety concerns.

In an Aug. 19 report covering the second quarter, The Wall Street Journal said Anthropic brought in $11.6 billion, more than double the previous quarter's sales. OpenAI earned $6.7 billion, up 18%, while its operating loss grew to $12.3 billion.