OpenAI brought Microsoft $10 billion in one quarter. A day later, Microsoft went back to the bond market.

Microsoft's quarterly report, filed with the SEC on Wednesday, October 28, puts a number on how much of its business now comes from one AI lab. Because Microsoft owns part of OpenAI, it has to disclose what it earns from it as a related party.

The OpenAI line (quarter ended September 30, 2026).

• Revenue from "commercial arrangements with OpenAI, inclusive of revenue-sharing payments": $10.0 billion. Total Microsoft revenue was $92.3 billion, so that is about 11%.
• For all of fiscal 2026 (the year to June 30), the same line was $24.1 billion. One quarter is now more than 40% of last year's total.
• OpenAI owed Microsoft $7.2 billion at the end of September, up from $6.0 billion at the end of June.
• Microsoft's stake is now about 24% on an as-converted basis, down from about 25% in its annual report. It has funded $12.0 billion of a $13.0 billion commitment.

The filing does not break that $10.0 billion down further, for example into Azure services versus revenue-sharing payments.

The rest of the AI picture. Azure revenue was $33.2 billion, up 48% from $22.4 billion. Commercial remaining performance obligation, contracts signed but not yet booked as revenue, rose 73% to $677 billion; Microsoft expects about 30% of it to turn into revenue in the next 12 months. Cash spent on property and equipment was $39.4 billion; CNBC reports $45.2 billion including finance leases, below the $50.7 billion analysts expected. Cash from operations was $58.0 billion, which leaves free cash flow of $18.6 billion, down 27% from $25.7 billion a year earlier (our math from the cash flow statement).

Then the bond sale. On Thursday morning Microsoft filed a preliminary prospectus for ten series of notes: two floating-rate and eight fixed-rate. The filing leaves sizes and rates blank and says proceeds are for "general corporate purposes," which may include capital expenditures, buybacks, acquisitions and repaying debt. Bloomberg, via Investing.com and Reuters, reports Microsoft is seeking at least $25 billion, its first U.S. high-grade bond sale since 2017. On Wednesday's call, finance chief Amy Hood said Microsoft "will access additional sources of funding" alongside its own cash, per The Seattle Times.

Our take. Microsoft is not short of money: it is still free cash flow positive, unlike Alphabet last quarter. But two things stand out. OpenAI is now a customer big enough to be about one dollar in nine of Microsoft's revenue, and it is also a company Microsoft part-owns. And the AAA-rated company that paid for its build-out from cash is now borrowing too. Watch the OpenAI line next quarter. $MSFT. Not investment advice.