# StackOne

> StackOne is a London-based integration platform that gives B2B SaaS companies and AI agent builders a single unified API to connect to hundreds of enterprise systems - from HR and CRM to ticketing, messaging and identity. Combining a proprietary tool-calling LLM with a real-time, privacy-first engine, it offers 200+ pre-built connectors and thousands of ready-made actions so agents can reliably and securely take actions inside the software businesses already use. Founded in 2023 by Romain Sestier and Guillaume Lebedel, the company raised a $20M Series A led by GV (Google Ventures) in May 2025 and has surpassed 1 billion API calls.

- **Founded:** 2023
- **Headquarters:** London, United Kingdom
- **Founders:** Romain Sestier (Co-founder & CEO), Guillaume Lebedel (Co-founder & CTO)
- **Team size:** ~53 employees (distributed across Europe and the United States)
- **Products:** Unified API, Tool-calling LLM, AI Integration / Connector Builder, Webhooks (native & synthetic), Open-source MCP servers & security tools
- **Notable:** Surpassed 1 billion API calls on the platform, Raised $24M total, including a $20M Series A led by GV (Google Ventures) in May 2025, Built a proprietary tool-calling LLM reporting 91.6% first-try accuracy on tool discovery

## Products & services

- **Unified API** — A single API to connect to 200+ enterprise SaaS systems across HR, CRM, ATS, ticketing, messaging and IAM, with thousands of pre-built actions.
- **Tool-calling LLM** — A proprietary model that helps AI agents discover and execute the correct action, reporting 91.6% first-try accuracy on StackOne's S1 Search Bench.
- **AI Integration / Connector Builder** — A builder that lets teams extend coverage to any API, creating custom integrations and authentication UIs.
- **Webhooks (native & synthetic)** — Real-time webhook forwarding, including synthetic webhooks for systems that don't natively support them.
- **Open-source MCP servers & security tools** — Open-source Model Context Protocol servers and prompt-injection detection tools contributed to the community.

## Achievements

- Surpassed 1 billion API calls on the platform
- Raised $24M total, including a $20M Series A led by GV (Google Ventures) in May 2025
- Built a proprietary tool-calling LLM reporting 91.6% first-try accuracy on tool discovery
- 200+ pre-built connectors and thousands of ready-made actions
- SOC2 Type II, HIPAA and GDPR compliant
- Customers across three continents including Drata, Attensi, Localyze and Mindtools

## Latest updates

- **2025-05** — Raised $20M Series A led by GV (Google Ventures), taking total funding to $24M.
- **2025-05** — Announced its proprietary tool-calling LLM with 91.6% first-try accuracy on the S1 Search Bench.
- **2025-05** — Surpassed 1 billion API calls on the platform.
- **2024** — Secured $3.6M seed round led by Episode 1 to build out the unified API and connector library.

## Links

- Website: https://www.stackone.com/
- LinkedIn: https://www.linkedin.com/company/stackonehq/
- Twitter/X: https://x.com/StackOneHQ
- GitHub: https://github.com/StackOneHQ

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Profile page: https://yespress.io/stackone
Published by YesPress — https://yespress.io
Last updated: 2026-07-10