Executive Summary:

• Microsoft disclosures and Bloomberg analyses show that OpenAI's compute spend and revenue share accounted for 70% or more of Microsoft's FY26 AI revenues, and more than 7% of Microsoft's overall FY2026 revenues.
• Microsoft has spent $261.3 billion in capital expenditures since the beginning of 2022.
• OpenAI accounted for $24.1 billion of Microsoft's FY2026 revenues.

As I discussed in yesterday's free newsletter, analyst estimates have OpenAI and Anthropic making up over 70% of all AI revenues across Microsoft, Google and Amazon.

While some might have disagreed, Bloomberg is now reporting that OpenAI "accounted for more than half, and likely about 70%, of Microsoft's actual AI sales during its most recent fiscal year."

Bloomberg's maths comes from Microsoft's Q3 statement that its AI annual run rate was $37 billion and the following disclosure from Microsoft's most-recent earnings:

For fiscal year 2026, we recorded revenue from commercial arrangements with OpenAI, inclusive of revenue sharing payments, of $24.1 billion, and accounts receivable from OpenAI as of June 30, 2026 was $6.0 billion.

To be clear, "run rate" means a non-specific month multiplied by 12, which means that it's very possible that Microsoft actually made far less than $37 billion, but based on that maths, OpenAI would make up roughly 64.8% - that being said, I think 70% or more is a perfectly-reasonable estimate, if not far, far more.

The other incredible fact from these disclosures is that OpenAI's spend and revenue share accounted for 7% of Microsoft's $331.8 billion in FY26 revenue - or around 7.26% to be specific.

At this point, it's impossible to argue that Microsoft has spent $270 billion in capital expenditures to prop up a single client, and that its overall AI plays have failed to create any significant revenue growth or opportunities.

We are now four years into the AI bubble, and Microsoft has little to show for it other than one very large and very unsustainable company that requires near-infinite resources to keep paying its cloud compute bills.