Mastra, a TypeScript agent framework, has closed a $13 million seed round backed by more than 120 investors. The funding was led by Y Combinator, with participation from Paul Graham, Gradient Ventures, and a long list of notable founders and institutional investors.
The round represents what the company describes as the largest post-YC cap table in several years. Notable participants include Dropbox cofounder Arash Ferdowsi, Vercel founder Guillermo Rauch, Replit CEO Amjad Masad, and former Coinbase CTO Balaji Srinivasan, alongside institutional backers like SVAngel, Orange Collective, and Runa Capital.
The founding team spent the last decade building Gatsby, a React-based framework used by hundreds of thousands of developers. Now they're applying those lessons to artificial intelligence infrastructure.
Mastra launched in January 2025 when the three cofounders joined Y Combinator. Within weeks, adoption began accelerating. By February, the framework started gaining serious traction among developers looking for better ways to build and deploy AI agents.
The new capital will support continued product development and team expansion. Mastra plans to scale its framework to meet growing demand from enterprise customers while maintaining the developer experience that drove early adoption.
The company is already seeing production deployments at major technology firms. Replit's Agent 3 uses Mastra to build agents at scale. SoftBank demonstrated a Mastra-based product on stage at a recent event. Marsh McLennan deployed an agentic search tool built with the framework to 75,000 employees.
Companies like PayPal, Adobe, Elastic, and Docker are either using Mastra in production or have written publicly about their implementations. The framework includes agent and workflow primitives, integrated playground tools, function calling, memory systems, evaluation frameworks, and tracing capabilities.
Mastra was founded by three former Gatsby team members who saw an opportunity to improve AI development tools. Kyle Mathews served as cofounder of Gatsby, while Abhi Aiyer was principal engineer and Shane Allen led product as staff engineer.
The trio started building Mastra in October 2024 after struggling with existing agent development tools. What began as a side project quickly became their primary focus when they realized the scale of the opportunity.
According to NPM data going back to 2015, Mastra is now the third-fastest-growing JavaScript framework ever measured. The company reached 150,000 weekly downloads in roughly one year. By comparison, Gatsby took four years to reach 190,000 weekly downloads.
As part of the funding round, the founding team recruited engineers they had worked with previously. The company is building out its technical team to support growing enterprise demand and expand the framework's capabilities.
Mastra also published a book titled "Principles of Building AI Agents" during its time at Y Combinator. The guide covers core concepts like agents, workflows, tools, memory, evaluations, and tracing. The company has distributed more than 70,000 physical copies and 100,000 digital downloads since March.
The investor list spans multiple categories, from legendary founders to emerging startups. Paul Graham participated directly, alongside unicorn founders like Tristan Handy of dbt, David Cramer of Sentry, and Alex Atallah of OpenSea.
Exited founders in the round include Rafael Garcia of Clever, Kulveer Taggar of Zeus, and Adrien Treuille of Streamlit. Current startup founders like Flo Crivello of Lindy, Michelle Valentine of Anrok, and Dex Horthy of HumanLayer also joined.
Institutional participants include basecase capital, Terrence Rohan, Palm Drive, Pioneer Fund, Liquid2, Defy, Lombardstreet, Scale Asia, Moonfire, and Transpose, among others. The company is hosting TS AI Conf in November in San Francisco, bringing together 300 builders with speakers including David Cramer, Michael Grinich, and Paul Klein.
