SaaStr 873: Agents Are Your New Power Users: How Klaviyo CEO Andrew Bialecki Is Remaking a $1.4B Business for the Agent Era

Before AI, Klaviyo had an insight that changed e-commerce marketing forever: don't show merchants how many emails they sent, show them how much money those emails made. That single shift helped Klaviyo capture 80% market share, earn a cult following among Shopify merchants, and IPO in 2023 with $1.4B in revenue.

Now Andrew has to do it again.

In this session at SaaStr AI Day, Klaviyo's co-founder and CEO breaks down how he's rebuilding a dominant pre-AI company for the agent era, including some of the most practical AI-at-scale lessons we've heard from any founder this year.

What's inside:

The Dark Factory. Klaviyo's internal agent system inspired by "lights-out manufacturing," where a team of agents decomposes a product prompt into specs, writes software interfaces, runs tests, handles load testing, and raises a flag only when it's genuinely stuck. One weekend, one agent team, one full prototype.

The Tom Brady Rule. Andrew's mental model for LLMs: treat them like a great all-around athlete. They'll never be elite without coaching. The "harness" you build around the model, the domain-specific data, feedback loops, and scoring, is what makes the difference between a POC and a product that works for 200,000 customers.

Agents skip onboarding entirely. Unlike human users who take months to learn a product, agents land as power users on day one. Andrew's team now asks their own agents, "What's holding you back?" and uses the answers to build their product roadmap. (One example: the agent discovered AMP interactive email on its own and immediately asked Klaviyo to build the missing APIs.)

Agents training agents. For customer-facing agents, Klaviyo takes a feed of real support cases, classifies them, then runs an agent loop that trains another agent on the platform, without any human FDE or SE required. It ships at 50-70% resolution out of the box.

APIs are the new UI. Whether your software is brand new or a decade old, if your internal and external APIs are great, agents will figure out the rest. The companies that win the agent era won't be the ones with the best interface. They'll be the ones with the best infrastructure.

Three years from now, every business will have an agent you can reach through a URL, a phone number, or an email. The question is who builds the infrastructure underneath it.