Microsoft's Anthropic stake earned $3.2 billion in one quarter. Its OpenAI stake earned $5 billion all year.

Microsoft's fourth-quarter earnings, reported July 29, contained an unusual data point: a real, dollar-denominated answer to a question that is normally unanswerable, because neither Anthropic nor OpenAI is public and neither publishes an independent valuation every quarter. Microsoft, as an investor in both, does the marking for them -- and this quarter its own accounting produced a $3.2 billion gain on the Anthropic stake against a $600 million markdown on the OpenAI stake, in the same three months.

A record quarter, an AI-heavy one

Microsoft's fiscal fourth quarter -- the three months to June 30, 2026 -- delivered $90 billion in revenue and $35.8 billion in net income, both records, with diluted earnings per share of $4.81, up 31% from a year earlier. For the full 2026 fiscal year, revenue reached $331.8 billion and net income $133.7 billion. Azure and other cloud-services revenue grew 43% for the quarter, its fastest pace since 2022, pushing Azure's full fiscal-year revenue past $100 billion for the first time.

Sitting inside those totals was Microsoft's $5 billion investment in [Anthropic](#/company/anthropic), made in November 2025 as part of an agreement under which Anthropic committed to buy $30 billion of Azure cloud services. Microsoft does not routinely revalue that stake every quarter -- so a $3.2 billion gain landing in a single quarter's results is itself the unusual event, not a recurring line item. CFO Amy Hood noted the gain alone exceeded the entire operating income -- $2.748 billion -- of Microsoft's More Personal Computing segment, the unit that contains Windows, Xbox, and Search.

The OpenAI side of the ledger

Microsoft's other AI stake moved the opposite way inside the same quarter. The company, which owns roughly 27% of [OpenAI](#/company/openai), marked that investment down $600 million, trimming diluted EPS by $0.07. The full fiscal year tells a different story: OpenAI's stake added $5 billion to Microsoft's results across FY26, boosting annual EPS by $0.67 -- meaning the quarter's markdown was a pullback within a year that was, on net, sharply positive.

Why a software company is booking swings on labs it doesn't run

Both marks are accounting artifacts of the same underlying arrangement: Microsoft holds minority stakes in two AI labs it doesn't control, and under the accounting treatment that applies to those stakes, changes in the labs' implied value flow through Microsoft's own income statement even though no cash changes hands. A funding round, a new investor's price, or a periodic remeasurement can move the number up or down without anything changing about Azure, Copilot, or any product Microsoft actually sells to a customer. That is why a single quarter's swing -- Anthropic up, OpenAI down -- is best read as a timing artifact of when each lab's valuation happened to move relative to Microsoft's own fiscal calendar, not a verdict on which lab is winning.

It also explains why the two labs' commercial arrangements with Microsoft look so different from the investment marks themselves. Anthropic's $30 billion Azure-purchase commitment and Microsoft's $5 billion stake were struck as one package in November 2025 -- a structure sometimes described as circular, since Microsoft's own cloud revenue benefits from money it partly supplied. That the Anthropic mark moved this quarter while OpenAI's did not says more about which lab's valuation event happened to fall inside Microsoft's fiscal Q4 than about either company's underlying trajectory. Both structures reflect the same fact: Microsoft is simultaneously an investor in, and a vendor to, the companies whose models it resells through Azure.

Microsoft's own public framing of the quarter undercuts any temptation to read the marks as picking a side. CEO Satya Nadella touted a catalog of "over 11,000 models" available through Microsoft's cloud, "including the latest from OpenAI, Anthropic, Mistral, xAI, as well as our own MAI family," and pointed to a fivefold increase since the start of the year in customers using more than one model provider through Microsoft's platform. Microsoft's commercial position depends on both labs staying viable customers and partners, not on either one outperforming the other.

Microsoft's own AI infrastructure spending dwarfed either investment mark. Cash capital expenditure on property and equipment hit $35.8 billion in the quarter -- more than double the $17.08 billion spent a year earlier -- and $115.95 billion for the full fiscal year, up from $64.55 billion in fiscal 2025. That spending helped fund the quarter's 43% Azure growth, itself an acceleration from 40% growth the prior quarter.

What this doesn't establish

It is tempting to read this quarter's numbers as proof Microsoft's Anthropic bet is outperforming its OpenAI bet, or as evidence of trouble at OpenAI. Neither reading holds up against the same disclosures.

The disclosure also lands the same week AI infrastructure stocks broadly sold off -- including [the fund run by former OpenAI researcher Leopold Aschenbrenner that leaned hard into the trade](#/article/aschenbrenner-situational-awareness-capital-raise-ai-rout) -- a reminder that even a company with a record quarter and two AI labs as partners is still exposed to how the market prices AI infrastructure broadly, not just to either lab's fortunes.

For a company that now discloses gains and markdowns on two AI labs in the same breath as its own record quarter, the more durable number is the one nobody had to explain with an accounting footnote: Azure growing 43% against a $115.95 billion capex bill. Whether Microsoft's bet on Anthropic or its bet on OpenAI looks smarter in hindsight will keep swinging quarter to quarter, on numbers neither company controls. Whether the spending on its own infrastructure was worth it depends on whether that growth rate holds -- and that is a number Microsoft answers for itself, every quarter, without needing anyone else's stake to move first.