Microsoft blew past Wall Street's targets for its fiscal first quarter, but the number that jumped out of Tuesday night's filings wasn't about Windows, Office or even the cloud. It was about OpenAI.

In results posted after markets closed on October 28, Microsoft reported revenue of $92.3 billion for the quarter ended September 30, up 19% from a year earlier and well ahead of analyst estimates near $90.7 billion. Net income rose 32% on a GAAP basis to $36.6 billion, or $4.92 a share. Azure revenue climbed 48%, Microsoft Cloud revenue hit $63.9 billion, and the company's commercial order backlog swelled 73% to $677 billion.

But buried in Microsoft's quarterly report filed the same day is a disclosure that has investors doing new math on just how entangled Microsoft and OpenAI have become. "For the three months ended September 30, 2026, we recorded revenue from commercial arrangements with OpenAI, inclusive of revenue-sharing payments, of $10.0 billion," the filing states — nearly 11% of Microsoft's entire quarterly revenue, up sharply from the roughly 7% share OpenAI represented for all of fiscal 2026.

A partner that's also a customer, and a debtor

The filing also shows OpenAI's unpaid balance to Microsoft climbing to $7.2 billion as of September 30, up from $6.0 billion three months earlier — a 20% jump in what OpenAI owes its biggest backer and infrastructure supplier. Microsoft holds roughly a 24% stake in OpenAI on an as-converted basis and has funded $12 billion of a $13 billion total commitment, money that flows back to Microsoft largely as cloud-computing fees.

The arrangement cuts both ways on the bottom line. A year ago, OpenAI-related losses dragged Microsoft's net income down by $3.1 billion; this quarter, a swing to a $207 million net gain on the investment added three cents to earnings per share. Strip out that OpenAI accounting noise entirely, and Microsoft's underlying profit growth was a more modest 18%, not 32%.

Capital spending tells a similar AI-driven story. Microsoft's additions to property and equipment roughly doubled year-over-year, to $39.4 billion from $19.4 billion, as the company keeps building out data centers to feed demand from OpenAI and its own Copilot products.

"We delivered a strong start to the fiscal year with Microsoft Cloud revenue of $63.9 billion, with growth accelerating to 30% year-over-year," said Amy Hood, Microsoft's chief financial officer, in the company's earnings release. "Results exceeded expectations across revenue, operating income, and earnings per share."

CEO Satya Nadella struck a similar tone, saying Microsoft is "translating our innovation into growing adoption and real-world impact across every industry." Wall Street largely agreed with the headline numbers: shares, which closed the regular session little changed at $531.01, climbed in after-hours trading as investors weighed the Azure beat against the capex jump.

Still, the OpenAI concentration is becoming impossible to ignore. On Microsoft's earnings call, Goldman Sachs analyst Gabriela Borges flagged the figure directly to Nadella, noting OpenAI now accounts for roughly 11% of quarterly revenue. The question investors are increasingly asking: what happens to Microsoft's growth story if OpenAI — a company it doesn't fully own, and which is racing to build its own independent infrastructure — eventually needs Microsoft's cloud less, or can't keep paying its bills on time.

Microsoft gave no new capex guidance in the release itself, saying only that details would come on its earnings call. With rivals Amazon and Alphabet also reporting this earnings season and racing to outspend each other on AI infrastructure, the next few quarters of Microsoft-OpenAI financial disclosures are likely to get just as much scrutiny as Azure's growth rate.