Batches & Eras

Launched in March 2005 from Cambridge, Massachusetts, YC ran startups through a single batch with a fixed three-month sprint and a closing Demo Day, deliberately writing tiny checks to young, technical founders. The model was an unproven experiment in funding many companies at once rather than meeting them one by one, and the early cohorts were small, scrappy, and run by hackers rather than financiers.

Signature: First batch (Summer 2005) funded Reddit and Loopt; Dropbox (S07) and Airbnb (W09) emerged from these formative years.

YC consolidated in Silicon Valley and rode the smartphone and cloud boom, when AWS and the App Store made it cheap to build and distribute software to a suddenly global, always-connected audience. Batches grew steadily and the firm's portfolio shifted from web toys toward infrastructure, marketplaces, and developer tools aimed at the new mobile-first internet.

Signature: Stripe (S09), Airbnb's breakout, and the rise of cloud and mobile-native marketplaces defined the period.

Sam Altman took over as president in 2014 and pushed YC to get much bigger, expanding batch sizes into the hundreds, standardizing the deal, and broadening into hardware, biotech, and international founders. YC became the default first stop for ambitious startups worldwide, with several portfolio companies maturing into household-name unicorns.

Signature: Altman's presidency, the standardized YC deal, and breakouts like Coinbase, DoorDash, and Instacart marked the scale-up.

Altman stepped down in 2019, and the COVID-19 pandemic forced YC to run its program and Demo Days fully remotely from 2020, accelerating a shift toward a more distributed, global founder base. Cheap money and a venture boom swelled batch sizes and valuations, even as the in-person community that had defined YC moved temporarily online.

Signature: Fully remote batches and virtual Demo Days from Summer 2020, amid a record venture-funding boom.

Garry Tan returned as CEO in January 2023, just as ChatGPT detonated a wave of AI startups, and YC retooled around the new generation of foundation-model applications. The firm tightened its batches and returned to its in-person, San Francisco roots, with roughly half of the Winter 2024 cohort building with AI.

Signature: Garry Tan's CEO return, the ChatGPT shockwave, and an AI-heavy Winter 2024 batch (~50% building with AI).

By 2025 AI was the default substrate rather than a niche, with cohorts dominated by founders building agents, AI tooling, and applications on top of rapidly improving models. Tiny, AI-leveraged teams could reach revenue and scale faster than any prior generation, reshaping what an early-stage startup looks like and how few people it takes to build one.

Signature: Agent-first and AI-tooling startups, and lean teams reaching scale with a fraction of the headcount.