Sublime Series C: $150M to fight email threats with AI agents

Email security firm Sublime just landed a massive $150 million Series C round to double down on its vision of fighting AI with AI. The funding, led by Georgian, signals a major validation for the company’s bet that the only way to defend against AI-supercharged phishing and social engineering is with autonomous agents that can think and adapt on their own.

The round comes as security teams grapple with a new reality. Attackers are now using generative AI to craft highly convincing, personalized attacks at a scale and speed that legacy email filters were never designed to handle. Sublime argues that the old model of static rules and slow vendor updates is broken.

AI agents on the front line

Sublime’s answer is what it calls “agentic email security.” Instead of just using AI models for detection, it deploys AI agents that act as extensions of a human security team. Its Autonomous Security Analyst (ASA) can autonomously triage user-reported phishing emails, clearing out the abuse mailbox backlog that plagues most organizations. Meanwhile, its Autonomous Detection Engineer (ADÉ) can proactively create and deploy new detection rules in response to emerging threats, a process that traditionally takes weeks of back-and-forth with a vendor.

This approach is resonating. According to a blog post by co-founders Josh Kamdjou and Ian Thiel, Sublime has quadrupled its customer base since the start of the year while maintaining zero enterprise customer churn since its inception. The new funding will be used to accelerate its agentic platform development and expand its global operations.

The round saw participation from new investors Avenir, 01A, and notable security figures Jon Oberheide and Nicole Perlroth, alongside existing backers like Index Ventures and IVP. It’s a clear sign that in the post-LLM world, investors are betting on proactive, autonomous systems to hold the line against an evolving wave of intelligent threats.