Microsoft booked a $3.2B Anthropic gain in one quarter. Its OpenAI stake slipped $600M.

Microsoft's Q4 FY2026 earnings, filed Wednesday, disclosed a $3.2 billion quarterly gain on its stake in AI lab Anthropic and a roughly $600 million write-down on its approximately 27% OpenAI position. The Anthropic mark-up added about $0.33 to diluted EPS; the OpenAI write-down reduced it by about $0.07.

The contrast is partly an accounting artifact. Microsoft does not mark its Anthropic stake to market every quarter, so the $3.2 billion revaluation landed in this filing rather than earlier ones. OpenAI is revalued each quarter, which is why its full-year moves aggregate neatly in Microsoft's filings. Anthropic is privately held; Microsoft's last disclosed round was a $5 billion investment in November 2025 that included a multi-billion dollar Azure purchase commitment from Anthropic.

The write-down is small against Microsoft's $35.8 billion in quarterly net income, and OpenAI remains a net positive for the full fiscal year: Microsoft recorded a $5 billion gain on OpenAI in FY2026, adding $0.67 to diluted EPS against a $17.95 full-year figure.

This is the first time Microsoft has put its two largest AI lab positions side by side in a single filing. The broader quarter was strong: $90.0 billion in revenue and $40.6 billion in operating income, both up 18% year over year.