Alexandr Wang started Scale AI to help machine learning teams label data faster.It started as a simple API for human labor, but behind the scenes, he was tackling a much bigger problem: how to turn messy, real-world data into something AI could learn from. Today, that early idea powers a multi-hundred-million-dollar engine behind America's AI infrastructure—fueling everything from Fortune 500 workflows to real-time military planning. Just last week, Meta agreed to invest over $14 billion in Scale AI, valuing the company at $29 billion.Alexandr joined us on the Lightcone to share how Scale AI evolved from a scrappy YC startup into the backbone of some of the world's most advanced AI systems, how he thinks about competition with Chinese AI labs, and what it takes to build infrastructure that shapes the frontier.

At first, prompting seemed to be a temporary workaround for getting the most out of large language models. But over time, it's become critical to the way we interact with AI.

On the Lightcone, Garry, Harj, Diana, and Jared break down what they've learned from working with hundreds of founders building with LLMs: why prompting still matters, where it breaks down, and how teams are making it more reliable in production.

They share real examples of prompts that failed, how companies are testing for quality, and what the best teams are doing to make LLM outputs useful and predictable.

The prompt from Parahelp (S24) discussed in the episode: https://parahelp.com/blog/prompt-design

There's never been a better time to start an AI company. Not just because there are new ideas, but because the tech finally makes old ones actually work.On the Lightcone, Garry, Harj, Diana, and Jared talk through the kinds of startups that are suddenly viable thanks to LLMs—from full-stack law firms to personalized tutors to recruiting platforms that can finally scale. They share the patterns they're seeing, the ideas they're excited about, and what it means to live at the edge of the future, where breakthroughs often look like second chances.If you've been waiting for the right moment to build, this is it.

Varun Mohan didn't set out to build one of the fastest-growing AI developer tools. He just knew his company had to change, or die.After initially betting on GPU virtualization, he saw the writing on the wall: if there was a future for his company, it would be at the AI application layer, not infra. Over a single weekend, he and his team pivoted to building Windsurf— a tool to help everyone, both technical and non-technical, write code faster and smarter.In this conversation, Varun shares the inside story of how they pivoted at the edge of failure, trained new models from scratch, outpaced giants like GitHub Copilot, and what the future of building with AI looks like.

Apply to Y Combinator: https://ycombinator.com/applyWork at a startup: https:/workatastartup.com

Technical skills build startups—but oftentimes, people skills can save them. So how do you navigate the disagreements and conflict that inevitably arise with a co-founder? In this episode of the Lightcone, our hosts share what they've learned for managing these critical, yet often overlooked challenges, offering advice on how to handle the messy realities that go beyond building.

Andrej Karpathy recently coined the term “vibe coding” to describe how LLMs are getting so good that devs can simply “give in to the vibes, embrace exponentials, and forget that the code even exists.” In this episode of the Lightcone, the hosts discuss this new method of programming and what it means for builders in the AI age.Apply to Y Combinator: https://ycombinator.com/apply

The Lightcone hosts sit down with Aaron Levie, the co-founder & CEO of Box, to hear reports from the front of how large enterprise and Fortune 500 companies are adapting to the AI age.

Apply to AI Startup School in SF: https://events.ycombinator.com/ai-sus

There’s never been a better time to launch an AI startup, but many prospective founders find themselves stuck when it comes to thinking of a good idea. In this episode, the Lightcone hosts look at different ways breakthroughs can be discovered.

Apply to Y Combinator: https://ycombinator.com/apply

In this special episode of Lightcone, we’re joined by YC partner and creator of Gmail, Paul Buchheit, to dig into some of the latest trends in the world of AI and startups.

We recorded our conversation at a recent retreat where 300 of the top AI founders in the world gathered to share expertise and make predictions about how this technology will shape our future.

In the discussion, we cover a wide range of topics, including the future of work, the power of agency and taste in an AI world, and why this is the absolute best time to be building a startup.

Happy New Year! In this mini-episode, the Lightcone hosts ring in 2025 with their predictions for startups, AI, crypto, and more.