The AI startups that customers will reliably shell out for are the ones that will ultimately survive and thrive.
Seems obvious enough, but it bears repeating in the AI industry’s financial funhouse-mirror landscape. ARR remains far from trustworthy, as the SaaS-era metric has been getting watered down: In some cases, companies fold in pilot revenue and one-time deals, bolstering the appearance of stability. Meanwhile, there’s a lot of anxiety around what it means for an AI tool to offer true ROI.
So I was intrigued by fintech Brex’s recent data outlining 2025’s 50 fastest-growing software vendors. The data is based on real spending, drawn from credit card and bill pay transactions from more than 35,000 anonymized Brex customers, that shows just who those customers are willing to pay for AI tools and services. The data weighs recent months more heavily to select for companies that didn’t just soar and crash at the beginning of 2025. The data also filters out public companies and companies worth more than $30 billion, so it covers the category of companies I most worry about in a bubble burst—the unicorns valued, more or less, between $5 and $25 billion. Big enough to matter, but not too big to fail.
“The goal isn’t just ‘who grew the most,’ but rather it’s ‘who grew the most and is likely to keep growing,’” said Sumeet Marwaha, Brex’s head of data, via email.
The fastest-growing software vendor in 2025: Cursor, valued north of $29 billion, came in at number one. The king of the coding juggernauts, Cursor saw 1,000% year-over-year growth in spending among Brex customers. Marwaha said that Cursor saw “spend compounding every single month of 2025. No other vendor in our data did that. Not one.”
It wasn’t just Cursor—coding tools as a category put up a substantial showing in the top 50. Windsurf (acquired by Cognition after initially agreeing to a deal with OpenAI) came in at No. 6, Replit at No. 9, CodeRabbit at No. 15, and StackBlitz at No. 36.
“This category basically didn’t exist two years ago,” Marwaha said. “Now there’s a paid, AI-powered coding environment that developers actually want and that managers are approving real budgets for.”
Marwaha said that the main factor in that rapid rise was “Friction. Or rather, the lack of it. Developers can run these tools locally. No IT approvals, no security reviews, no six-month procurement death march. Download it, use it, see the value immediately.”
Some other notable and surprising shoutouts: No. 2 was OpenRouter, a less well-known AI model marketplace, which saw 1,500% year-over-year spending growth on Brex. Other names drawing dollars at the infrastructure layer include Vast.ai (No. 11), Groq (No. 12), Supabase (No. 23), and Sentry(No. 33).
The natural question, just days before Christmas, is how this will all play out in 2026. Marwaha’s betting on visual AI. In 2025, AI video production tool provider Kling.ai came in at No. 3, while Ideogram and Runway made the list at No. 17 and No. 44 respectively. The idea is that these visual and video platforms could follow the no-friction coding tool playbook.
“The winners in 2026 won’t just be general-purpose generators,” Marwaha told Fortune. “They’ll be tools that nail a particular use case so well that teams can’t go back to the old way.”
See you tomorrow,
Allie Garfinkle X: @agarfinks Email: [email protected] Submit a deal for the Term Sheet newsletter here.
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The post As AI investors fret over ROI, these startups attracted serious cash from customers in 2025 appeared first on Fortune.
