StackOne, an AI agents startup based in London, has raised a $20m Series A funding round led by Google Ventures (GV).
Almost halfway through 2025, investor enthusiasm for AI agents — applications which use large language models (LLMs) to automate tasks without a human in the loop — shows little sign of abating.
In the first six weeks of 2025 alone, European startups building AI agents picked up €481m — more than a quarter of the funds raised by such startups in the entire year previous, according to Sifted data.
Founded by two former Google employees, CEO Romain Sestier and CTO Guillaume Lebedel, StackOne’s focus is integration, a multi-billion dollar industry dedicated to helping businesses make all the enterprise tools they use work in harmony, from internal messaging tools to HR portals and supply chain management.
StackOne has developed an AI agent which can be used to connect disparate parts of a client’s tech stack, which they say rapidly speeds up companies’ adoption and integration of new applications.
“We have felt the acute pain of integrations. We saw teams burn months rebuilding or refusing requests and nothing on the market eased this pain,” says Sestier, describing his and Lebedel’s time at Google. “We believe AI agents are the missing piece in finally delivering enterprise-grade integrations at scale.”
Alongside GV, StackOne was backed by Workday Ventures and XTX Ventures, while also winning funding from existing investors Episode 1 and Playfair. Angels from OpenAI, Google DeepMind and Microsoft also participated, the company said.
“Romain and Guillaume aren’t building just another SaaS integration platform. They’re creating infrastructure that modern software and the entire AI agent ecosystem can rely on,” says Luna Schmid, Partner at GV.
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