Two Customers Account for a Fifth of Anthropic's Revenue, a Concentration Risk IPO Buyers Should Know

Anthropic, one of the world's fastest-growing AI companies, plans to go public by the end of the year. It's reportedly targeting a $2 trillion valuation, which would make it the largest IPO in history and one of the world's most valuable companies.

However, the recent leaks from its confidential S-1 filing reveal some bright red flags. In the first half of 2026, it reportedly generated $16.3 billion in revenue, but it posted a staggering net loss of $80.7 billion. $72 billion of that loss came from non-cash accounting charges, but it still raises troubling questions about its claim to have achieved "adjusted" profitability in its third quarter.

Image source: Getty Images.

Moreover, about a fifth of its revenue in the first half of 2026 came from just two customers. Anthropic didn't name either company in its S-1 filing, but several industry reports have identified them as SpaceX (NASDAQ: SPCX) and Microsoft (NASDAQ: MSFT). Let's see why these two companies rely on Anthropic, and if that concentration is a major long-term risk.

Why are SpaceX and Microsoft relying on Anthropic?

SpaceX's AI business acquired Cursor, an AI coding start-up, for $60 billion in August. Cursor's AI-first code editor allows its users to access Anthropic's Claude AI models.

Microsoft integrates Claude into GitHub Copilot, an AI-powered programming assistant initially developed by GitHub and OpenAI. As GitHub expanded its platform to include other AI models, millions of developers routed their requests through Claude.

Anthropic generates revenue whenever those platforms access Claude's API (application programming interface). As more developers use Claude's tools on Cursor and GitHub Copilot to accelerate their programming tasks, Anthropic's revenue will keep rising.

Is this a major risk for Anthropic?

Claude's programming models (especially Sonnet and Opus) are widely regarded as the best AI tools for generating complex code, so even though Cursor and GitHub Copilot users can select other AI models -- including OpenAI's GPT, Alphabet's Google Gemini, and SpaceX/xAI's Grok -- the vast majority of programmers still use Claude.

But according to Anthropic's S-1 filing, its largest customers access its models on a usage-based basis with no long-term contracts. Therefore, if any of Anthropic's competitors catch up and launch comparable coding models at lower prices, its revenue could plummet. If that competition forces it to reduce its prices, its net losses will likely widen.

Anthropic will inevitably attract a lot of attention when it finally goes public. But just like SpaceX, that sentiment could cool off when investors start to notice its glaring weaknesses.

Leo Sun has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Alphabet and Microsoft. The Motley Fool has a disclosure policy.