Background: How Anthropic Seized the Enterprise Lead
For most of the period between 2023 and late 2025, <cite index="24-3,24-4">Anthropic tripled its enterprise Large Language Model (LLM) market share to 40%, up from 12% in 2023, while OpenAI fell from 50% to 27% over the same period</cite>. That shift was documented in Menlo Ventures' *2025 State of Generative AI in the Enterprise* report, published in December 2025, which measured enterprise LLM Application Programming Interface (API) spend across providers.
<cite index="27-8,27-9,27-10">Anthropic's ascent was driven by durable dominance in the enterprise coding market, where it commanded an estimated 54% share compared to 21% for OpenAI — up from 42% six months earlier — propelled largely by Claude Code and an almost unparalleled 18 months atop LLM leaderboards for coding.</cite> Menlo Ventures partner Deedy Das noted at the time: <cite index="23-2,23-3,23-4">"The era of automatic OpenAI wins is over, and it may be hard for anyone to catch Anthropic. They've dominated coding for 18 months straight — a $4 billion category that's become the gateway to enterprise workflows across every department and industry. And from what we've seen, once an enterprise chooses a vendor, they tend to stay."</cite>
The turning point for Anthropic among paying business customers came in May 2026. <cite index="17-5,17-6,17-7">OpenAI, which was once the runaway leader with both businesses and consumers, lost the lead among Ramp's paying business users in May, when Anthropic hit 41% market share to OpenAI's 39% — a lead OpenAI had never regained.</cite>
The Q3 2026 Shift
<cite index="17-4">Ramp, the corporate credit card and expense management company, has released new data showing OpenAI has started gaining on Anthropic with U.S. businesses.</cite> <cite index="17-1">According to Ramp economist Ara Kharazian, OpenAI is currently growing faster among this business-user segment in Q3 to date than Anthropic.</cite> The Ramp dataset is drawn from actual business card transactions, giving it an independence from vendor self-reporting that makes it a closely watched proxy for enterprise AI spend.
OpenAI has been building out its enterprise footprint aggressively. <cite index="19-3,19-4,19-5">In an April 2026 enterprise blog post, OpenAI Chief Revenue Officer Denise Dresser noted that enterprise now makes up more than 40% of the company's revenue and is on track to reach parity with consumer revenue by the end of 2026, while the Codex agentic coding agent hit 3 million weekly active users and OpenAI APIs processed more than 15 billion tokens per minute.</cite> <cite index="19-6">New enterprise customers cited in the post include Goldman Sachs, Philips, and State Farm, alongside expanding relationships with Cursor, DoorDash, Thermo Fisher, and LY Corporation.</cite>
On headline user metrics, <cite index="15-1">OpenAI reported over 9 million paying business users and 1 million paying business customers worldwide, which the company described as "the fastest-growing business platform in history."</cite> <cite index="15-3,15-4">ChatGPT Enterprise seats grew 9× year-over-year in 2025, while weekly messages in ChatGPT Enterprise grew approximately 8× year-over-year.</cite>
Anthropic's Position Remains Strong
Despite the Q3 momentum shift, Anthropic retains structural advantages. <cite index="9-5,9-6">By April 2026, Reuters reported that Anthropic's annualized revenue run rate had surpassed $30 billion, and the company said the number of enterprise customers spending more than $1 million annually had doubled to over 1,000.</cite> <cite index="10-6">Anthropic also reported that 8 of the Fortune 10 are Claude customers, with over 300,000 business customers in total and 500+ at $1 million or more in annualized spend.</cite>
<cite index="13-2">Combined with Anthropic's reported $74.1 billion Annual Recurring Revenue (ARR) overtaking OpenAI's $41.3 billion in July 2026, analysts noted it was the first time Anthropic had led on every major commercial metric except total user count.</cite> Both figures are run-rate estimates rather than audited financials, as neither company has yet completed a public offering.
What the Data Does and Does Not Show
The Ramp dataset captures a slice of U.S. corporate spending and does not encompass global enterprise API spend or direct contracts. <cite index="17-2,17-3">With still a month left in the quarter and both OpenAI and Anthropic yet to release formal financials ahead of planned initial public offerings, third-party spend proxies remain among the few independent signals available.</cite> The competitive picture may shift further as both companies expand their model lineups and enterprise go-to-market programs through the remainder of 2026.