The core flow metric is clear: in April, businesses spent more on Anthropic than OpenAI for the first time. The data from Ramp's AI Index shows Anthropic reached 34.4% business adoption while OpenAI's adoption fell to 32.3%. This crossover marks a dramatic reversal from just a year ago, when OpenAI was the dominant enterprise choice.
The growth trajectory explains the shift. Anthropic's adoption has quadrupled over the past year, a surge powered by tools like Claude Code. OpenAI's growth, by contrast, has been minimal, with adoption rising just 0.3% in the same period. This flow crossover is a major signal for the AI market, showing a tangible shift in corporate spending patterns.
Yet the victory may prove fragile. The same report that crowns a new leader warns that AI competition remains unusually volatile, with businesses rapidly switching models based on cost and performance. The broader AI adoption rate among Ramp's business customers rose to 50.6%, indicating the market is still in flux.
Revenue Run-Rate: The Engine Behind the Flow
The spending shift is powered by staggering financial scale. In April, Anthropic achieved a $30 billion annualized run-rate, surpassing OpenAI's $24 billion. This explosive growth is not from consumer virality but from enterprise contracts, with Anthropic's run-rate soaring from just $9 billion at the end of 2025.
The growth trajectories are unprecedented. Anthropic's run-rate more than doubled from February to April, a surge that Meritech's Alex Clayton notes has no precedent in software history. OpenAI's climb is steep too, moving from $2 billion in monthly revenue last year to its current run-rate. Both companies are scaling at a pace that defies traditional benchmarks.
The engine is B2B adoption. OpenAI's enterprise segment is now over 40% of its revenue, while Anthropic built its entire base on API deals and tools like Claude Code. This focus on durable, high-ACV contracts is what allows Anthropic to pass OpenAI on run-rate despite having a fraction of its consumer user base. The money is in the enterprise.
Fragility and Risks: The Flow Breakdown
The flow crossover is a snapshot, not a guarantee. The very pricing model that fuels Anthropic's revenue growth creates a vulnerability. Its token-based system means the company profits more from expensive model runs, a structure that could trigger cost pushback as businesses face escalating bills. This dynamic is already at play, with users reporting outages and declining quality with Claude.
The competitive pressure is accelerating. OpenAI is responding with aggressive price hikes, like the 92% increase for GPT-5.5. Such moves are designed to accelerate customer migration and protect margins, directly challenging Anthropic's enterprise lead. At the same time, cheaper inference platforms running open-source models are gaining traction, offering alternatives that can undercut the cost of proprietary APIs.
The next data point will be critical. The upcoming June Ramp AI Index release will show whether Anthropic's 34.4% share holds or slips. The index tracks spending, not usage, so any reversal could signal that cost sensitivity is outweighing brand momentum. In a market where newcomers can disrupt leaders in months, the flow can break as quickly as it built.