Y Combinator
American startup accelerator founded in 2005 by Paul Graham, Jessica Livingston, Trevor Blackwell and Robert Morris, known for its seed-funding model and Demo Day, and led since 2023 by CEO Garry Tan.
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- Established
- 2005
- Location
- San Francisco, California, United States
- Country
- United States
- Founded
- 2005, in Cambridge, Massachusetts, near Harvard University
- Founders
- Paul Graham, Jessica Livingston, Trevor Blackwell, Robert Morris
- Current headquarters
- Pier 70, Dogpatch neighborhood, San Francisco (moved from Mountain View in spring 2023)
- President and CEO
- Garry Tan (since January 2023)
- Standard investment
- $500,000 per company: $125,000 for 7% equity on a post-money SAFE, plus $375,000 on an uncapped SAFE with a most-favored-nation clausestated by the subject
- Program length
- Cohort-based accelerator program, cohorts held four times a year as of 2024, culminating in "Demo Day"
Overview
Y Combinator is an American startup accelerator founded in 2005 by Paul Graham and Robert Morris — who had previously co-founded the e-commerce company Viaweb, sold to Yahoo in 1998 for roughly $50 million — together with Jessica Livingston and Trevor Blackwell, starting as a summer program near Harvard University in Cambridge, Massachusetts, before relocating to Mountain View, California (Forbes). It has since become one of the best-known startup accelerators in the United States, running cohort-based programs that culminate in a pitch event known as “Demo Day” (Forbes). Y Combinator moved its headquarters again in spring 2023, after 17 years in Mountain View, to Pier 70 in San Francisco’s Dogpatch neighborhood (Fortune).
Business model
Y Combinator funds cohorts of startups in exchange for equity. As reported in 2010, the accelerator was then investing “$11,000, plus $3,000 per founder,” for about 5% equity, selecting roughly 40 companies out of about 1,000 applicants per cohort, with each startup given about two-and-a-half minutes to pitch investors at Demo Day (Forbes). Terms have changed since: in November 2022, then-president Geoff Ralston said Y Combinator was raising its standard investment from $125,000 to $500,000 per company, timed to help startups survive a deteriorating fundraising market (TechCrunch). Y Combinator’s own website currently describes that $500,000 as split between $125,000 for 7% equity on a post-money SAFE and a further $375,000 on an uncapped SAFE carrying a most-favored-nation clause (Y Combinator). Under CEO Garry Tan, the accelerator also changed its cohort structure: in 2024 it moved from running two batches a year to four, shortening each program from about twelve weeks to about nine (Inc.).
Notable alumni companies
Early Y Combinator cohorts included Airbnb, which went through the accelerator’s winter 2009 batch for a $20,000 investment in exchange for a 6% stake and went public in 2020 at a $47 billion valuation, and DoorDash, a member of the summer 2013 cohort, whose 2020 initial public offering at a $39 billion valuation was, at the time, the first Y Combinator company exit worth more than $10 billion (Crunchbase News). By December 2020, Crunchbase News reported that Y Combinator had invested in more than 2,500 companies since its 2005 launch with an initial cohort of 8, and that its portfolio then included 29 companies valued as unicorns plus 11 more approaching that valuation (Crunchbase News). These figures are specific to the date of that reporting and are not restated here as current totals.
Leadership: Altman, Ralston, and Tan
Sam Altman joined Y Combinator as a part-time partner in 2011 and became its president in February 2014, succeeding co-founder Paul Graham, who had led the organization for its first nine years (TechCrunch). Altman left Y Combinator in 2019, the same year OpenAI — where Altman had also been involved since 2015 — announced a for-profit subsidiary with Altman as its CEO (Forbes). Accounts of that departure differ: Paul Graham has publicly rejected the word “fired,” saying instead that Jessica Livingston presented Altman with a choice between running Y Combinator and running OpenAI, which he accepted amicably; Forbes reported that The Washington Post, citing three sources, said Graham removed Altman over concerns he was prioritizing his own interests, and quoted former OpenAI board member Helen Toner describing the episode as having been “hushed up at the time” (Forbes). More on Altman’s subsequent career is covered in his own profile.
Geoff Ralston succeeded Altman as Y Combinator’s president and CEO around 2019 and served in that role until the end of 2022 (TechCrunch). On August 29, 2022, Y Combinator announced that Garry Tan — a 2008 YC founder who later worked as a YC partner from 2010 to 2015 advising roughly 700 companies, and who went on to co-found the venture fund Initialized Capital after having previously co-founded Posterous, acquired by Twitter in 2012 — would succeed Ralston as president and CEO, taking over in January 2023 (TechCrunch; Y Combinator).
Recent developments under Garry Tan
In spring 2023, shortly before that year’s summer batch, Y Combinator relocated its headquarters from Mountain View — where it had been based for 17 years — to Pier 70 in San Francisco’s Dogpatch neighborhood. Tan said the move kept Y Combinator close to AI companies such as OpenAI and Anthropic, which are based in San Francisco rather than Silicon Valley, and noted that most YC partners, including himself, already lived in the city (Fortune).
On January 28, 2024, Tan posted, then deleted, a message on X naming seven San Francisco supervisors — Chan, Peskin, Preston, Walton, Melgar, Ronen, and Safai — that included the phrase “die slow motherfuckers.” He apologized afterward, attributing the language to a rap-lyric reference and saying “there is no place, no excuse and no reason for this type of speech and charged language in discourse.” Supervisor Myrna Melgar publicly described the language as “rattling” (TechCrunch).
Under Tan, Y Combinator also expanded from two cohorts a year to four in 2024, shortening each program from about 12 weeks to about 9 weeks; batch sizes reported for this period include 94 companies in the fall 2024 cohort and 170 in the summer 2025 cohort. The large majority of these startups have been AI-focused — about 85% of the fall 2024 cohort and about 90% of the summer 2025 cohort, by one count — and Y Combinator has said full batches have repeatedly hit double-digit weekly revenue growth (Inc.).
What this profile does not claim
This profile does not resolve the conflicting accounts of Sam Altman’s 2019 departure from Y Combinator — it states Paul Graham’s account and the differing Washington Post/Helen Toner account (as reported by Forbes) side by side, without asserting which is correct. It does not describe Geoff Ralston’s presidency as “interim,” since the sources read here describe him simply as president and CEO from 2019 to 2022. It does not give Robert Morris’s fuller name or academic affiliation, since no independently fetched source used for this profile confirmed those details beyond the name “Robert Morris.” It does not state a current total number of companies funded or a current combined portfolio valuation; the only such figures available to this profile (2,500+ companies, 29 unicorns) are explicitly dated to December 2020 and are not current. It does not cover Y Combinator’s full roster of notable alumni companies beyond Airbnb and DoorDash, and it does not address internal Y Combinator partner dynamics beyond the specific, disputed circumstances of Altman’s 2019 exit described above.
Timeline
- 2005
- Founded in Cambridge, Massachusetts, by Paul Graham and Robert Morris (previously co-founders of Viaweb, sold to Yahoo in 1998 for roughly $50 million), together with Jessica Livingston and Trevor Blackwell, as a summer program funding startups founded mainly by college students.
- 2009
- The accelerator, by this point operating out of Mountain View, California, funds Airbnb's winter cohort with $20,000 for a 6% stake.
- 2011
- Sam Altman joins Y Combinator as a part-time partner.
- 2013
- DoorDash goes through Y Combinator's summer cohort; it later becomes the first YC company to have a public-market exit worth more than $10 billion.
- 2014
- Sam Altman becomes president of Y Combinator, succeeding co-founder Paul Graham, who had led the organization for its first nine years.
- 2019
- Altman leaves Y Combinator as OpenAI announces a for-profit subsidiary with him as CEO; Geoff Ralston becomes Y Combinator's president and CEO. Accounts differ on the circumstances of Altman's departure (see below).
- 2020
- By this point Y Combinator has invested in more than 2,500 companies since 2005 (it launched with 8), including 29 companies then valued as unicorns and 11 more approaching that valuation; Airbnb and DoorDash both go public this year at multibillion-dollar valuations.
- 2022-08-29
- Y Combinator announces that Garry Tan, a former YC partner and YC alumnus founder, will succeed Geoff Ralston as president and CEO, effective the following January.
- 2023-01
- Garry Tan formally takes over as Y Combinator's president and CEO.
- 2023-04
- Y Combinator relocates its headquarters from Mountain View, where it had operated for 17 years, to Pier 70 in San Francisco's Dogpatch neighborhood, ahead of that year's summer batch.
- 2024-01-28
- Garry Tan posts, then deletes, a message on X naming seven San Francisco supervisors and including the phrase "die slow motherfuckers"; he apologizes, attributing the language to a rap lyric reference.
- 2024
- Under Tan, Y Combinator expands from two cohorts a year to four, shortening each program from about twelve weeks to about nine; the large majority of startups in the 2024–2025 cohorts are AI-focused (roughly 85–90% by one count).
What we could not verify
These claims came up in research and could not be confirmed. They are recorded here rather than published as fact or quietly dropped. If you hold a source that settles one, please tell us.
- Sources disagree on the framing of Sam Altman's 2019 departure from Y Combinator. Paul Graham has publicly said Altman was not "fired," and describes Jessica Livingston presenting Altman with a choice between Y Combinator and OpenAI, which Altman accepted amicably. The Washington Post, as reported by Forbes, cited three sources saying Graham removed Altman from Y Combinator over concerns that Altman was prioritizing his own interests, and quoted former OpenAI board member Helen Toner describing the episode as having been "hushed up at the time." This profile states both accounts without resolving which is accurate.
- Geoff Ralston's presidency is sometimes described elsewhere as an "interim" role, but the sources read for this profile (TechCrunch's 2022 reporting, including Ralston's own remarks) describe him simply as Y Combinator's president and CEO from 2019 to the end of 2022 — not as an interim officer — so this profile does not use the word "interim."
- Robert Morris is widely identified elsewhere (including in Wikipedia, which is not cited here) by the fuller name "Robert Tappan Morris" and as an MIT computer science professor. No tier1/tier2/tier3 source independently fetched for this profile confirmed the middle name or his academic title, so this profile uses only "Robert Morris," the form used by the Forbes source, and does not state his MIT affiliation.
- Total-companies-funded and combined-valuation figures change constantly and are only available to this profile as dated snapshots (2,500+ companies and 29 unicorns as of December 2020). No source independently read for this profile gave a comparable up-to-date total as of 2026, so no current figure is stated.
- No source independently read for this profile addressed the specific, often-discussed internal Y Combinator partner dispute involving Sam Altman prior to his 2019 departure beyond the "fired vs. not fired" dispute already described above; this profile does not assert further detail about internal 2018–2019 partner dynamics.
Sources
11 sources (8 tier 1, 1 tier 2, 2 first-party), each opened and read against the claim it supports. Statements the subject makes about itself are marked as such and are not treated as independent evidence. See the source policy.
Every source below was independently fetched and read against the specific claim it supports. No Wikipedia page was used as a source; Wikipedia search results were used only to identify leads, which were then followed to independent, directly-fetched sources. Where sources disagreed on the nature of Sam Altman's 2019 departure, both accounts are given rather than resolved. Figures on total companies funded, valuations, and unicorn counts are attributed to the date of the reporting that produced them and are not presented as current.
- The Disruptor In The Valley Supports: Y Combinator's 2005 founding near Harvard in Cambridge, Massachusetts; its four founders (Paul Graham, Robert Morris, Jessica Livingston, Trevor Blackwell); Graham and Morris's earlier company Viaweb and its 1998 sale to Yahoo for roughly $50 million; the accelerator's later move to Mountain View, California; and its business model at the time (roughly $11,000 plus $3,000 per founder for about 5% equity, around 1,000 applications for about 40 spots per cohort, and the structure of Demo Day).
- Sam Altman Taking Over As President Of Y Combinator, Replacing Paul Graham At The Helm Supports: Sam Altman's move from part-time partner (a role he had held since 2011) to president of Y Combinator in 2014, and Paul Graham's stepping down after leading the organization for nine years.
- Garry Tan is the next president and CEO of Y Combinator Supports: The August 29, 2022 announcement that Garry Tan would succeed Geoff Ralston (Y Combinator's president and CEO since 2019) effective the following year; Tan's background as a 2008 YC founder, a YC partner from 2010–2015 who worked with roughly 700 companies, co-founder of Initialized Capital and of Posterous (acquired by Twitter in 2012), and an early Palantir employee.
- Outgoing YC president Geoff Ralston: 'The market is changing, YC's terms are not' Supports: Confirmation that Ralston served as Y Combinator's president and CEO from around 2019 until his planned departure at the end of 2022, with Garry Tan set to take over in January 2023; and Y Combinator's 2022 increase in per-company standard investment from $125,000 to $500,000.
- Sam Altman Wasn't Fired From Y Combinator, Founder Claims, As OpenAI Chief Faces Criticism From Ex-Board Member Supports: Paul Graham's public statement disputing that Altman was "fired" from Y Combinator, his account that Jessica Livingston gave Altman a choice between Y Combinator and OpenAI, and Forbes's reporting that The Washington Post (citing three sources) and former OpenAI board member Helen Toner gave a differing account in which Graham removed Altman over concerns about divided loyalties; and that Altman's 2019 exit coincided with OpenAI creating a for-profit subsidiary with him as CEO.
- How the AI Bubble Ate Y Combinator Supports: Confirmation that Garry Tan became CEO in 2023; Y Combinator's 2024 expansion from two cohorts a year to four, with each program shortened from about 12 weeks to about 9; batch sizes (94 companies in fall 2024, 170 in summer 2025); the concentration of AI startups in recent cohorts (about 85% and 90% respectively); and Y Combinator's own claims about batch-wide weekly revenue growth.
- Y Combinator president Garry Tan publishes a menacing tweet before deleting it, apologizing: 'Die slow motherf*ckers' Supports: The January 28, 2024 post by Garry Tan naming seven San Francisco supervisors (Chan, Peskin, Preston, Walton, Melgar, Ronen, and Safai) and including the phrase "die slow motherfuckers"; his deletion of the post and apology attributing the language to a rap-lyric reference; and Supervisor Myrna Melgar's public response describing the language as "rattling."
- Garry Tan and the Founders of Y Combinator Explain Why They Moved Headquarters Supports: Y Combinator's spring 2023 move of its headquarters to Pier 70 in San Francisco's Dogpatch neighborhood after 17 years in Mountain View, and Garry Tan's stated reasoning tied to proximity to AI companies such as OpenAI and Anthropic.
- Y Combinator's biggest exits, from Airbnb's IPO to DoorDash's blockbuster debut Supports: Airbnb's participation in Y Combinator's winter 2009 cohort for $20,000 and a 6% stake and its 2020 IPO; DoorDash's participation in the summer 2013 cohort and its 2020 IPO as YC's first exit worth more than $10 billion; the figure that Y Combinator had invested in more than 2,500 companies since its 2005 launch with an initial 8 companies; and the count of 29 unicorn-valued portfolio companies plus 11 approaching that valuation, as of December 2020.
- Welcome Home, Garry Tan Supports: Y Combinator's own announcement of Garry Tan's appointment, the January 2023 effective date, and Ralston's account of Tan's prior role as a YC partner working alongside him for five years.
- YC's Deal Supports: Y Combinator's own current statement of its standard investment terms: $500,000 per company, split between $125,000 for 7% equity on a post-money SAFE and $375,000 on an uncapped SAFE with a most-favored-nation clause.
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