Microsoft’s AI business is booming. But peel back the numbers and you’ll find that roughly 70% of that growth traces back to a single partner: OpenAI.

OpenAI’s revenue has hit approximately $24.1 billion on an annualized basis in fiscal 2026, translating to about $2 billion rolling in every month.

The numbers behind the partnership

Microsoft’s broader AI business is running at somewhere between $37 billion and $40 billion in annualized revenue as of mid-2026. If OpenAI accounts for 70% of the AI sales portion, the math is straightforward: remove OpenAI from the equation and Microsoft’s AI story looks dramatically different.

Microsoft reported that OpenAI-related commitments represented roughly 45% of its $625 billion commercial cloud backlog as of Q2 fiscal year 2026. That’s not a typo. Nearly half of Microsoft’s future cloud revenue pipeline is tied to one company.

OpenAI closed a record $122 billion funding round on March 31, 2026, which pushed its post-money valuation to $852 billion. Microsoft participated in that round alongside Amazon, NVIDIA, and SoftBank.

The revenue engine is primarily ChatGPT subscriptions and API usage. Enterprise customers are paying for access to OpenAI’s models through Microsoft’s Azure cloud platform.

A restructured relationship

In April 2026, Microsoft and OpenAI restructured their partnership agreement, reducing exclusivity provisions and capping revenue-sharing arrangements through 2030.

What this means for investors

The 70% figure is both Microsoft’s greatest strength and its most obvious vulnerability right now. The OpenAI partnership has effectively given Microsoft a multi-year head start in enterprise AI adoption.

When nearly half your cloud backlog and the vast majority of your AI revenue depend on one partner’s continued success and loyalty, you’re exposed to concentration risk. Revenue-sharing caps through 2030 give both sides predictability, though they also put a ceiling on Microsoft’s upside if OpenAI’s revenue continues its exponential climb.

OpenAI’s $852 billion valuation and $24 billion revenue run rate set a benchmark that every competitor, from Anthropic to Google DeepMind, will be measured against. The $122 billion funding round also signals that private capital markets remain deeply committed to AI infrastructure plays.