Y Combinator is the most influential startup accelerator in the world, founded in 2005 by Paul Graham, Jessica Livingston, Robert Tappan Morris, and Trevor Blackwell. Originally split between Cambridge, Massachusetts and Mountain View, California, YC consolidated in Silicon Valley and is now headquartered in San Francisco. YC runs a three-month program four times a year (winter, spring, summer, fall), each batch typically funding 250-300 early-stage startups. Its standard deal invests $500,000 in every company: $125,000 for 7% of the company on a post-money SAFE, plus $375,000 on an uncapped SAFE with a Most Favored Nation (MFN) provision. YC has funded more than 5,000 companies with a combined valuation exceeding $600 billion, including Airbnb, Stripe, Coinbase, DoorDash, Instacart, Dropbox, Reddit, Twitch, GitLab, and Ginkgo Bioworks. The firm is led by president and CEO Garry Tan, a General Partner and himself a YC alum. YC is sector-agnostic but heavily developer-tools, AI, fintech, B2B/SaaS, infrastructure, healthcare, and hard-tech oriented, and its alumni network of 6,000+ founders, plus Demo Day, Startup School, Work at a Startup, and Hacker News, form the connective tissue of the modern startup ecosystem.
Firms are ranked by cumulative portfolio strength — how many highly-rated API companies they've backed, weighted by tier across composite quality and agent-readiness. The averages below are a secondary read on the typical company in the book.
Y Combinator has 839 portfolio companies tracked on the APIs.io network, of which 293 (35%) publish APIs indexed here. The remaining 545 are tracked as profiles without a published API on the network.
Its highest-rated API providers on the network are Algolia, Stripe, Gitlab, Optimizely, Doordash.
Portfolio on the Network
Portfolio companies that publish APIs indexed on APIs.io, grouped by their
API Evangelist rating. Exemplar and Strong are expanded by default.
Exemplar15Complete, well-documented, and agent-ready
The 731 portfolio companies with APIs in the catalog, backed by
Y Combinator, scored on the Kin Score. Every figure below is computed from
the catalog — nothing here is written.
A facet is averaged over the members that carry it, not over the whole cohort — the
“Scored” column is that count. Averaging an absent facet as zero would score our own
coverage gaps as the providers’ posture.
What this cohort publishes
Artifact
This cohort
Catalog
Difference
MCP server (any)
24%
15%
+9
MCP server (first-party)
23%
12%
+11
Agent Skills
0%
0%
0
OAuth scopes
11%
11%
0
Security
99%
98%
+1
Arazzo workflows
4%
2%
+2
Governance rules
6%
13%
-7
mcp_pct counts any mcp/ artifact including ones API Evangelist derived from the provider OpenAPI; mcp_first_party_pct counts only servers the provider publishes. Prefer the latter.
This roster declares 838 members; 821
resolve to a provider in the catalog and 731 carry a score
(89%). The figures above describe the scored members only. Coverage caveat. 683 of 731 scored members had under half their catalog-attributable points satisfied at all (catalog_earned / catalog_max < 0.5). They are INCLUDED in the mean above. A large share here means the cohort mean is partly a measurement of how far our enrichment reached, not only of how these providers publish.Generated from the catalog build of
3 October 2026, across 28834
providers, using the same computation served by the
APIs.io cohort API. Briefs are published for rosters of
5 or more scored providers; below that a distribution is not meaningful.
aid: y-combinator
name: Y Combinator
description: >-
Y Combinator is the most influential startup accelerator in the world, founded
in 2005 by Paul Graham, Jessica Livingston, Robert Tappan Morris, and Trevor
Blackwell. Originally split between Cambridge, Massachusetts and Mountain View,
California, YC consolidated in Silicon Valley and is now headquartered in San
Francisco. YC runs a three-month program four times a year (winter, spring,
summer, fall), each batch typically funding 250-300 early-stage startups. Its
standard deal invests $500,000 in every company: $125,000 for 7% of the company
on a post-money SAFE, plus $375,000 on an uncapped SAFE with a Most Favored
Nation (MFN) provision. YC has funded more than 5,000 companies with a combined
valuation exceeding $600 billion, including Airbnb, Stripe, Coinbase, DoorDash,
Instacart, Dropbox, Reddit, Twitch, GitLab, and Ginkgo Bioworks. The firm is
led by president and CEO Garry Tan, a General Partner and himself a YC alum. YC
is sector-agnostic but heavily developer-tools, AI, fintech, B2B/SaaS,
infrastructure, healthcare, and hard-tech oriented, and its alumni network of
6,000+ founders, plus Demo Day, Startup School, Work at a Startup, and Hacker
News, form the connective tissue of the modern startup ecosystem.
x-type: venture-capital
x-category: Accelerator
deliveryModel:
model: unknown
open_source: false
commercial: false
callable_host: false
label: Delivery model not determined — needs a product licence on record
confidence: low
source:
- none
generated: '2026-08-28'
method: derived
accessModel:
pricing: unknown
onboarding: unknown
trial: false
try_now: false
public: false
label: Unknown
confidence: low
source: []
generated: '2026-07-22'
method: derived
image: https://www.ycombinator.com/apple-touch-icon.png
created: '2026-07-17'
modified: '2026-07-17'
specificationVersion: '0.23'
tags:
- Venture Capital
- Accelerator
- Seed
- Developer Tools
- Artificial Intelligence
- Fintech
- Infrastructure
- B2B SaaS
- North America
- San Francisco
apis: []
common:
- type: Website
url: https://www.ycombinator.com
- type: Portfolio
url: https://www.ycombinator.com/companies
- type: Portfolio
url: portfolio/y-combinator-portfolio.yml
- type: Team
url: https://www.ycombinator.com/people
- type: Team
url: team/y-combinator-team.yml
- type: InvestmentThesis
url: https://www.ycombinator.com/about
- type: Blog
url: https://www.ycombinator.com/blog
- type: Pitch
url: https://www.ycombinator.com/apply
- type: Jobs
url: https://www.workatastartup.com
- type: Crunchbase
url: https://www.crunchbase.com/organization/y-combinator
- type: LinkedIn
url: https://www.linkedin.com/school/y-combinator/
- type: Twitter
url: https://twitter.com/ycombinator
- type: GitHubOrganization
url: https://github.com/ycombinator
- type: Contact
url: https://www.ycombinator.com/contact
- type: Features
data:
- 'Model: Accelerator (3-month program, 4 batches per year)'
- 'Stage: Pre-seed, Seed'
- 'Typical check: $500,000 standard deal ($125K for 7% post-money SAFE + $375K uncapped SAFE with MFN)'
- 'Batch size: 250-300 startups per batch'
- 'Sectors: developer tools, AI, fintech, B2B SaaS, infrastructure, healthcare, hard tech (sector-agnostic)'
- 'Geography: primarily North America; global applicants'
- 'Companies funded: 5,000+ (combined valuation $600B+)'
- 'Founded: 2005'
- 'HQ: San Francisco, CA'
sources:
- https://www.ycombinator.com/about
- https://www.ycombinator.com/deal
- https://en.wikipedia.org/wiki/Y_Combinator
updated: '2026-07-17'
maintainers:
- FN: Kin Lane
email: kin@apievangelist.com
url: https://apievangelist.com
- FN: APIs.json
url: http://apisjson.org
- FN: Y Combinator
url: https://www.ycombinator.com
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