OpenAI just told its own employees that Microsoft, the company that funded its existence, held it back.

In a memo obtained by CNBC, newly appointed OpenAI Chief Revenue Officer Denise Dresser told staffers that the Microsoft partnership has "limited our ability to meet enterprises where they are." The fix? Amazon. The demand for OpenAI on Amazon Web Services has been "frankly staggering" since the $50 billion deal was announced in February.

Read that again. OpenAI is publicly telling its employees that its founding corporate partner was a constraint. Microsoft invested over $13 billion in OpenAI before most people knew what a large language model was. And now? OpenAI is running into Amazon's arms while sending internal memos calling the relationship that built the company a liability.

But the real heat in the memo is aimed at Anthropic.

Dresser accused Anthropic of building its strategy on "fear, restriction, and the idea that a small group of elites should control AI." She then alleged Anthropic is inflating its revenue by approximately $8 billion through accounting practices that gross up revenue sharing with Amazon and Google. OpenAI, Dresser claimed, reports its Microsoft rev share net, "more in line with standards we would be held to as a public company."

Translation: Anthropic says it hit $30 billion in annualized revenue. OpenAI is calling that number fake.

This matters because both companies are racing toward IPOs that could happen this year. OpenAI was valued at $852 billion in late March. Anthropic hit $380 billion in February. The enterprise market is the battlefield, and the numbers each company reports will determine whether investors buy the pitch or bail.

The timing is brutal for OpenAI. At the HumanX AI conference in San Francisco last week, Glean CEO Arvind Jain described the industry mood around Claude as "Claude mania." He added: "It has become a religion, that is the level of that mania." Enterprise customers are choosing Anthropic. Google Gemini is pushing hard. OpenAI is watching its dominance evaporate in the one market that matters for an IPO narrative.

So OpenAI did what any company in trouble does: it found a richer patron. Amazon is bringing $50 billion and exclusive third-party cloud distribution for OpenAI Frontier, its enterprise agent platform. That is not a partnership. That is a lifeline.

Dresser told CNBC earlier this month that enterprise now makes up 40% of OpenAI revenue and is on track for parity with consumer by year-end. But the memo reveals something the earnings pitch does not: OpenAI could not close those deals effectively while locked inside Microsoft Azure. The Amazon deal was not a strategic expansion. It was an escape.

Here is the bigger picture. OpenAI just confirmed what the entire industry suspected: Microsoft is no longer the kingmaker. It backed OpenAI with billions, embedded it in every Office product, built Copilot around it, and in return got a partner that now tells employees the relationship was holding them back.

Microsoft declined to comment. But it does not need to. It already announced it was building its own AI models. The divorce is not coming. It already happened. This memo is just the paperwork.

First reported by CNBC.