Y Combinator

About

Y Combinator (YC) is a startup accelerator founded on March 11, 2005, by Paul Graham, Jessica Livingston, Robert Tappan Morris, and Trevor Blackwell ¹². The idea originated when Graham and Livingston conceived the concept while walking home from dinner in Harvard Square; Graham contributed $100,000, while Morris and Blackwell each invested $50,000, launching the experiment with $200,000 in initial capital ¹.

The first batch (Summer 2005) funded 8 teams out of 25 applicants, including the teams behind Reddit and Loopt ¹². YC initially ran concurrent programs in Cambridge, Massachusetts, and Mountain View, California, but consolidated to Silicon Valley in January 2009 ³. The accelerator operated from Mountain View for 17 years before relocating its headquarters to San Francisco’s Dogpatch neighborhood in spring 2023 ⁴.

YC’s leadership has changed several times. Paul Graham led the organization until 2014, when Sam Altman became president ². Altman was succeeded by Geoff Ralston in 2019, who was in turn replaced by Garry Tan as president and CEO in January 2023 ⁵⁶. In March 2024, Michael Seibel stepped down as managing director and was succeeded by Jared Friedman ⁶.

In October 2015, YC launched the Continuity Fund, a $700 million growth-stage vehicle that made follow-on investments in YC alumni companies with check sizes of $20 million to $100 million ⁷⁸. The Continuity Fund was led by Ali Rowghani and later Anu Hariharan ⁸. In March 2023, under Garry Tan’s leadership, YC wound down the Continuity Fund and laid off approximately 20% of staff, refocusing on its core accelerator program ⁷. Tan also initiated a consolidated fundraising effort with a stated goal of raising $2 billion across new funds ⁶.

As of 2026, Y Combinator has funded 5,668 startups across its history, with a combined portfolio valuation exceeding $600 billion ⁹¹⁰. The accelerator has produced 82 unicorns (companies valued at $1 billion or more), 17 companies that have gone public, and maintains a roughly 69% active company rate ⁹¹⁰. YC now runs four batches per year (Winter, Spring, Summer, Fall), each containing approximately 150-250 companies ⁹¹¹.

Stated Thesis

Y Combinator’s motto is “Make something people want” ¹². The accelerator publicly positions itself as backing founders at the earliest stage, providing seed funding, mentorship, and access to a network of alumni and investors.

Paul Graham articulated YC’s founding philosophy: “investors should be making more, smaller investments, they should be funding hackers instead of suits, they should be willing to fund younger founders” ¹. Graham has described what YC looks for in founders across five traits: determination (“what matters most is determination”), flexibility, imagination, “naughtiness” (a willingness to break conventions), and friendship between co-founders ¹³.

Garry Tan has stated that YC looks for “first principles thinkers — founders who not only believe what no one believes yet, but figure out what’s necessary to build, whether software or distribution, to create something no one else sees” ¹⁴. Tan champions what he calls “ambitious misfits” and values earnestness over polish in founders ¹⁴¹⁵.

YC states it invests in companies “twice a year” (now four times per year) across all sectors and geographies, with no restrictions on industry or business model ¹². The accelerator emphasizes that it does not charge any fees to participating companies and that its investment is not contingent on hitting milestones ¹⁶.

Inferred Thesis

The following analysis is based on YC’s publicly available portfolio data. With 5,668 total companies funded ⁹, constructing a complete portfolio analysis is impractical, but aggregate data from YC’s own directory and third-party analyses provides strong signal.

Sector Allocation

Based on analysis of 5,668 companies in YC’s directory ⁹:

• B2B / Enterprise SaaS: 4,788 companies (84.5%) — YC has shifted overwhelmingly toward B2B over time. Recent batches are over 75% B2B companies ¹⁰.
• Consumer: 862 companies (15.2%) — Consumer companies were more prevalent in early batches (2005-2012) but have declined significantly as a share of each batch.
• Top specialized sectors by count: Healthcare (653 companies, 11.5%), Fintech (606 companies, 10.7%), Industrials (347 companies, 6.1%), Education (241 companies, 4.3%) ⁹.
• AI/ML concentration: In the Summer 2025 batch, 141 of 169 startups (83%) were classified as AI-native companies ¹¹. Overall, AI companies represent approximately 60% of recent 2025-2026 batches, up from 15% just two years prior ¹¹¹⁷.

Stage Distribution

YC invests exclusively at the pre-seed/seed stage through its accelerator program. Every company receives the identical standard deal regardless of stage, traction, or sector ¹⁶. The now-defunct Continuity Fund (2015-2023) made growth-stage investments at Series B and later ⁷⁸.

Geographic Concentration

• US-based companies: 68.9% of total portfolio ⁹.
• San Francisco concentration: Rose from 20.9% of companies in 2021 to 73.0% in 2026, reflecting the return to in-person batches and the SF headquarters move ⁹⁴.
• International presence: YC accepts companies from anywhere and provides assistance with US incorporation. Companies must incorporate in the US, Canada, Cayman Islands, or Singapore ¹⁶.

Check Size and Terms

YC’s standard deal is $500,000 per company, split across two SAFEs ¹⁶: - $125,000 on a post-money SAFE for 7% equity - $375,000 on an uncapped SAFE with a Most Favored Nation (MFN) provision

YC also receives pro rata rights for subsequent funding rounds ¹⁶. This deal has been consistent since approximately 2022 ¹⁸.

Batch Size and Volume

YC invests at extraordinarily high volume compared to traditional venture firms: - Smallest batch: 8-11 companies (Summer 2005) ¹⁹ - Largest single batch: ~399 companies (Winter 2022) ⁹ - Peak annual output: 727 companies (2021) ⁹ - Recent annual output: ~600 companies (2024-2025) ⁹¹¹ - Winter 2026 batch: 196 companies ¹¹

Founder Profile Patterns

• Solo founders have declined from historical norms to approximately 10% of recent batches ¹⁰.
• Median founding team size has trended toward 2-3 co-founders ⁹.
• YC has historically favored technical founders, consistent with Graham’s stated preference for “hackers instead of suits” ¹.
• Recent batches show increasing numbers of repeat YC founders and founders from top CS programs ¹¹.

Success Rates

• Approximately 4.5% of YC companies become unicorns, versus 2.5% for other venture-backed seed-stage startups ¹⁰.
• Around 45% of YC companies secure Series A funding, versus 33% average for seed-stage startups ¹⁰.
• Over 50% of YC companies remain active after 10 years, versus 30% average ¹⁰.
• The top 4 public companies (Airbnb, DoorDash, Coinbase, Instacart) account for 84% of YC’s total public market value ¹⁰.

Notable Gaps Between Stated and Actual Thesis

• Sector-agnostic claim vs. AI dominance: YC claims to invest across all sectors, but recent batches are 60-83% AI companies ¹¹¹⁷. While this may reflect applicant pool composition, it represents a significant de facto concentration.
• Geographic openness vs. US concentration: Despite accepting international companies, 69% of the portfolio is US-based, and SF concentration has increased dramatically under Tan’s leadership ⁹⁴.
• Consumer decline: YC’s early identity was built on consumer hits (Reddit, Airbnb, Dropbox), but the portfolio has shifted overwhelmingly to B2B (84.5%), with consumer companies now representing just 15% of the portfolio ⁹.
• Power law concentration: The vast majority of YC’s financial returns come from a tiny fraction of companies. The top 4 public companies represent 84% of public market value ¹⁰, suggesting that YC’s model depends on extraordinary outliers rather than consistent portfolio performance.

Portfolio

The following table includes 120 notable Y Combinator companies, organized by batch year. YC has funded 5,668 companies total ⁹; this table represents approximately 2.1% of the full portfolio, focused on the most notable investments including all known unicorns and major exits.

Note: This table represents approximately 2.1% of YC’s 5,668 total investments ⁹, focused on the most notable companies including unicorns, public companies, and significant acquisitions. YC’s standard deal gives it 7% equity in every company at the same terms, making a complete portfolio listing impractical. Batch years use the YC batch designation (e.g., W09 = Winter 2009, S12 = Summer 2012). Some companies (OpenAI, Duolingo, Plaid) have batch information not publicly confirmed and are listed without batch designation.

In Their Own Words

Paul Graham on founding YC:

“Investors should be making more, smaller investments, they should be funding hackers instead of suits, they should be willing to fund younger founders.” ¹

Paul Graham on what YC looks for in founders:

“What matters most is determination. You’re going to hit a lot of obstacles. You can’t be the sort of person who gets demoralized easily.” ¹³

“Most good ideas seem bad initially. If they were obviously good, someone would already be doing them.” ¹³

“Startups do to the relationship between the founders what a dog does to a sock: if it can be pulled apart, it will be.” ¹³

Garry Tan on what YC looks for:

YC partners look for “first principles thinkers — founders who not only believe what no one believes yet, but figure out what’s necessary to build, whether software or distribution, to create something no one else sees.” ¹⁴

Garry Tan on AI’s impact:

“AI transformed software from a ‘nice to have’ into an urgent necessity.” ¹⁵

Sam Altman on execution speed:

“The best founders execute so quickly.” ²³

Michael Seibel on YC’s level playing field:

“What I love about Y Combinator is that it is a level playing field. If you get in, you immediately become a Silicon Valley insider.” ²⁴

What Founders Say

Patrick Collison, Co-Founder of Stripe (S09):

“I doubt that Stripe would have worked without YC. It’s that simple. Acquiring early customers, figuring out who to hire, closing deals with banks, raising money — YC’s partners were closely involved and crucially helpful.” (Source: YC Quotes page) ²²

Brian Chesky, Co-Founder of Airbnb (W09):

“At YC, we were challenged to do things that don’t scale — to start with the perfect experience for one person, then work backwards and scale it to 100 people who love us.” (Source: YC Quotes page) ²²

Eric Migicovsky, Founder of Pebble (W11):

“I arrived in Silicon Valley in 2011 and was instantly enveloped in the YC network. From connections to founders, mentors, investors and employees to invaluable advice from the partners, applying to YC was the single most critical decision we ever made at Pebble.” (Source: YC Quotes page) ²²

Chase Adam, Founder of Watsi (W13):

“I can’t imagine any startup that wouldn’t benefit tremendously from Y Combinator’s support. To this day, joining Y Combinator was the best decision we’ve made at Watsi.” (Source: YC Quotes page) ²²

Jessica Mah, CEO of inDinero (S10):

“YC was the experience of a lifetime. I came in with a prototype and left with a real business. The PR contacts, investor relationships, and entrepreneur camaraderie helped me level up my CEO skills faster than I could have even imagined.” (Source: YC Quotes page) ²²

Tracy Young, Co-Founder of PlanGrid (W12):

“YC motivated PlanGrid to focus on the single thing that mattered — building something people love and finding product market fit.” (Source: YC Quotes page) ²²

Elizabeth Iorns, Founder of Science Exchange (S11):

“Y Combinator was a gamechanger for us. We entered the program with an idea and, 3 months later, left as a launched company with seed funding from the best investors in Silicon Valley.” (Source: YC Quotes page) ²²

Dave Rogenmoser, Founder of Proof (YC):

“Absolutely yes. I would do it over again.” (on whether giving up 7% equity and relocating was worth the Y Combinator experience) (Source: Proof blog, 2019) ²⁵

Sachin Rekhi, Founder of Anywhere.FM (S07):

“Y Combinator is an amazing program for a young first time entrepreneur who is serious about jump starting the entrepreneurial experience.” He noted that “the culminating Investor Day is by far one of the most valuable aspects of the YC program” and that “one of the most remarkable phenomenons is the bond that is created between fellow entrepreneurs who have gone through a shared experience.” (Source: sachinrekhi.com) ²⁶

Anonymous W22 founder (critical perspective):

A founder from the Winter 2022 batch reported that “the program has turned into a conveyor, pushing everyone through the same pipeline with one partner for 20 companies on average,” noting limited personalized support and that office hours sometimes yielded only generic advice. (Source: Substack review, 2022) ²⁷

Marc Andreessen, Co-Founder of Andreessen Horowitz (investor perspective):

“Several of our best investments have come from Y Combinator. Y Combinator is the best program for creating top-end entrepreneurs that has ever existed.” ²⁴

Note: The Collison, Chesky, Migicovsky, Adam, Mah, Young, and Iorns quotes are sourced from YC’s own quotes page, which is a curated and biased source — these represent the accelerator’s selected testimonials. The Rogenmoser and Rekhi quotes are independently sourced from their own blogs. The anonymous W22 criticism is from an independent Substack post. The Andreessen quote is from an investor, not a founder, but is included for context.

Sources