Discover the next generation of startups.

Experiential Labs

YCombinator

World models for agents

An applied AI research lab building world models for agents. We simulate reality faster and more accurately based on the technology self-driving uses to get 99.7% reconstruction fidelity.

Experiment

YCombinator

crowdfunding platform for science

Today's funders are so conservative they only fund the most obvious ideas. At Experiment, we fund the ideas that they won't fund; the ideas that matter. Since founding, over 47,000 citizens have pledged $9 million dollars supporting 900 scientific projects on the platform. 46% of all projects on Experiment are successfully funded. When the projects are finished, the scientists share the scientific results with their backers as lab notes and peer-reviewed publications. Scientists from Stanford, Harvard, and Yale have chosen to use Experiment instead of writing grants. Bill Gates recognized Experiment by saying "this solution helps close the gap for potentially-promising but unfunded projects."

F2

YCombinator

The AI platform for private markets investors

F2 is the AI platform for private markets investors. Purpose-built for private credit, private equity, and commercial banking, F2 accelerates diligence, underwriting, and portfolio monitoring, helping teams evaluate deals over 60% faster. F2 turns unstructured deal data into investment-grade analysis and polished memos in minutes. Unlike general-purpose AI, F2 is built with the domain expertise and depth to handle the most complex financial analysis. Already trusted across thousands of deals, F2 makes collaboration easy and retains historical context, so past work compounds into future wins. Headquartered in New York City, F2 is backed by leading investors including NFX, Left Lane Capital, and Y Combinator.

F4 Industries

YCombinator

The GD&T Analysis Platform for Engineering Drawings

GD&T takes years to master. Engineers must encode their design intent into a dense syntax that manufacturers must decode, and not everyone gets it right. Put ten engineers in front of the same drawing and you may get ten different interpretations. Which means errors often surface later in interface stack-ups, manufacturing, or in the field - when they’re far more expensive to fix. That’s why we built F4 - the platform that analyzes GD&T to determine whether your designs are ready for production. Drop in your drawing and 3D file. F4 analyzes every element of your GD&T to assess whether your design is clear, manufacturable, and production ready. To make the drawing easier to understand, engineers can visualize their datums, reference frames, and tolerance zones directly on the 3D model. F4 also calculates tolerance stack-ups instantly - directly from the drawing. What once took hours of manual work now takes seconds. When issues are found, F4 flags them and guides engineers toward resolving the problem. After analyzing your drawing, F4 also automatically generates design and inspection reports - stack-up tables, FAI reports - ready to share with your team. And it does all of this locally on-device with no AI used for analysis. Producing deterministic results engineers can trust.

Fabraix

YCombinator

The world's frontier hacker for AI agents.

Fabraix builds state-of-the-art AI red-teaming agents that continuously detect security vulnerabilities in customer-facing AI. Our product, Nyx, has already found vulnerabilities in agents at dozens of Fortune 500 companies. On AgentHarm, the leading benchmark for offensive AI security, Nyx achieved a 78% attack success rate, compared with 67% for GPT-5.6 Sol. Companies usually pay for penetration tests one project at a time. They select which systems to include, give a team a few weeks to find vulnerabilities, and receive a report when the project ends. Testing everything this way is very expensive. Globally, penetration tests cover only 26% of the software attack surface. AI agents can change more often than teams can test them. A new model, prompt, tool, permission, or data source can change what an agent does, even when the application code stays the same. The report describes only the version that was tested. AI is also increasing how much software companies produce and how often it changes. We built Nyx to automate this work. It does three things: 1. Nyx connects through the same interfaces customers use. It tests chat, voice, browser, and coding agents without source code or a special integration. 2. It draws on more than 10,000 jailbreaks that we have collected and classified, the largest such library we know of. 3. It uses each response to decide what to try next and can pursue a promising approach for hundreds of turns. In our tests, these adaptive attacks succeeded 20 times as often as attacks that were replayed unchanged or stopped after a fixed number of turns. Nyx often finds its first vulnerability within minutes or hours rather than days or weeks. Because the work is automated, companies can repeat the test with every change and at much lower cost. We're also the team behind ACE (Adversarial Cost to Exploit), a benchmark that measures AI security in terms of how much it costs attackers to break an AI system; providing a game-theoretic framework to understand how motivated a rational attacker would be in exploiting the system.

Faire

YCombinator

The global online platform empowering independent retail.

Faire is an innovative online marketplace that uses machine learning to match local retailers with the brands and products that uniquely fit their stores. We are using the power of technology to connect brands and independent retailers from all over the world, building a thriving community of hundreds of thousands of retailers, which has resulted in over 7 million new connections to date. Faire was founded on the belief that the future of retail is local. Our mission is to empower brands and retailers to strengthen the unique character of local communities. Our data-driven approach unburdens retailers from decades-old obstacles by helping find the right products for their shop. Plus, our straight-forward financial terms level the playing field by eliminating inventory risk and providing access to capital—key offerings previously only available to big box chains. For brands, our platform provides powerful sales, marketing, and analytics tools that simplify their business and allow them to focus on what they love: making great products.

Fastshot

YCombinator

Lovable for mobile apps

Fastshot is a no-code mobile development platform. Our mission is to "Democratize mobile app creation with AI" Anyone can develop a mobile app from idea to App Stores within minutes just by chatting with AI.

Fed10

YCombinator

AI Agents for Government Affairs

Fed10 is a legislative consulting firm staffed by AI agents. We monitor every bill across the U.S., flag threats to your business, and deliver actionable insights — the same work a $500/hr policy consultant does, but in seconds instead of days. Built by three ex-lobbyists who passed legislation together.

Fenrock AI

YCombinator

AI agents for banks

We're building the Legora for traditional financial services, working closely with US bank CEOs to transform their businesses.