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Fastest growing S21 companies

The 100 YC S21 companies whose team grew the most in the last 6 months (active companies with 10+ people).

Updated weekly, last on November 9, 2026. Roster from Y Combinator's public directory.

Showing 100 of 100 companies on this list
#CompanyTeam6 mo12 moOpen rolesTotal raisedLast round
1
AI engineering capacity. Made simple. ⚡️
10+100% YCPre-seedAug 2021
2
The AI-Native Turnkey Alternative Investment Platform (TAIP)
29+93%+142%YC$18.9MSeries A$15M, Sep 2026
3
AI-enabled financial automation and intelligence for CPG Brands
121+89%+163%22$75MSeries B$55M, Sep 2026
4
Accelerate software development with WarpBuild's 10x faster CI infra.
12+71%+71%1$1.5MPre-seed$1.5M, Aug 2021
5
AI native ATS + CRM for executive search firms
10+67%+100%YC$2.1MSeed$2.1M, Jan 2025
6
AI Business Analysts to gather requirements and optimize processes
19+58%+73%YC$4.4MNon-equity support$4.3M, Mar 2026
7
The global financial platform for affluent consumers in the Americas.
277+49%+147%24
8
Web search rebuilt for LLMs
243+46%+117%28$357MSeries C$250M, May 2026
9
Plaid for Brazil: we allow developers to access users' financial data
48+33%+71%0$5.2MSeries A$3.5M, Aug 2026
10
Salary on-demand platform for Latin America
20+33%+67%0$125KYC investment$125K, Aug 2021
11
Banking, corporate cards, stablecoin payments, available globally.
98+31%+63%3$160MSeries C$100M, Apr 2026
12
We're building fully automated labs for protein engineering
40+29%+43%YC$50.9MSeries A$40M, Aug 2026
13
Speech and accent coaching app for non-native English speakers
27+29%+69%2$27.1MSeries A$21M, Dec 2025
14
AI-Powered ERP, MES, and Test Software for Complex Operations
42+27%+45%YC$18.8MSeries A$15M, Jun 2022
15
Orbital logistics: Unleashing space industry, from Earth to asteroids
34+26%+3%YC$9.5MUndisclosed round$2.5M, Sep 2025
16
AI-native on-call and incident response carefully crafted to help…
93+22%+27%1$15.2MSeries A$12M, Aug 2023
17
Easiest way for companies to process data requests from governments
99+22%+62%5$41.2MSeries A$21.2M, Sep 2025
18
Software that helps employees pick their employee benefits.
34+21%+36%0$11.1MSeries A$7.8M, Jul 2022
19
Unlocking the next generation of mRNA medicines
35+21%+35%0$70.9MSeries A$20M, Oct 2026
20
Turning space into a transportation layer for Earth
131+20%+30%3$54.3MSeries A$44M, Nov 2024
21
TURN STATIC DOCS INTO INSTANT ANSWERS
18+20%+13%0$3MSeed$2M, Feb 2022
22
Developer friendly drop in payouts infrastructure
18+20%+50%YC$14.8MSeries A$8.9M, Feb 2026
23
Autonomous medical care
40+18%+60%15$7.6MSeed$5.6M, Jan 2026
24
One source of truth for financial data.
107+18%+45%1$46.1MSeries B$29.2M, Sep 2025
25
One stop investment solution for retail investors in Latam
63+17%+17%1$7.9MUndisclosed round$3M, Jun 2025
26
Autonomous Stratospheric UAVs
21+17%+17%YC$450KSeed$450K, Jan 2023
27
Native user-facing SaaS integrations for your customers
22+16%+5%0$5.6MSeed$4M, Oct 2024
28
Flexible Business Apps for Modern Teams
22+16%+22%YC$5.4MSeed$4M, Aug 2024
29
Patent-pending enzymes to break down common dietary triggers
15+15%+36%0$1.6MSeed$1.5M, Oct 2021
30
Help ML teams label the right data
38+15%+15%YC$3.1MSeed$3M, May 2022
31
We make injections as easy as pushing a button!
31+15%+29%YC
32
Robots that build solar farms
31+15%+24%15$17MUndisclosed round$17M, Aug 2024
33
Empowering local businesses to sell online.
47+15%+24%0$4.2MSeed$4.1M, Feb 2022
34
AI Copilot for insights & strategy
24+14%+33%YC
35
Virtual Co-working Community
17+13%+13%0$5.1MSeed$5M, Jul 2022
36
Learning app for school students in Southeast Asia
157+13%+15%0$1.7MSeed$1.6M, Jan 2022
37
Payments and scheduling for services professionals in LATAM
186+13%+28%0$1.6MSeed$1.5M, Nov 2021
38
AirBnB for Small Warehouses
71+13%+42%0$2.8MUndisclosed round$2M, Sep 2025
39
One API to get clean data from any website for your AI agents at scale
160+13%+27%0$2MSeed$2M, Dec 2021
40
Online Training for Healthcare Jobs
449+12%+33%36$111MSeries C$55M, Jun 2026
41
Flexible On-Demand Storage Space for Household, SMEs & Travellers.
85+12%+20%0$630KSeed$505K, Dec 2021
42
We visually monitor space objects for governments and defense
125+12%+21%0$38.4MSeries B$26.4M, Sep 2026
43
AI CAD Software for Civil Engineering
40+11%+21%8$16.8MSeed$14.4M, Jul 2024
44
Make all team work visible, people and AI agents
10+11% 0Pre-seedAug 2021
45
The UAE’s leading small business payments platform
62+11%+24%0$3.4MSeed$3.4M, Nov 2021
46
Amazon Level Logistics for eCommerce Companies in MENA.
126+11%+8%0$2.6MPre-seed$2.4M, Oct 2021
47
The everything app for LATAM
1,132+10%+27%1$71MSeries A$47M, Jun 2022
48
Account Receivables Platform for Latin American Enterprises
367+10%+27%14$66.5MSeries A$48M, Apr 2025
49
Saving OPS from SLOPS. Jestor builds internal systems that last.
23+10%+44%0$345KYC investment$345K, Aug 2021
50
Online University for Tech Professionals
23+10%+10%0SeedAug 2021
51
We help Accountants automate work and serve their customers online
83+9%+9%1$2.7MSeed$2.2M, Mar 2022
52
Demo operations for the AI era
36+9%+50%YC$2.1MSeed$2.1M, Apr 2023
53
Reinventing respiration monitoring
12+9%+9%0$164KEquity crowdfunding$39K, Mar 2023
54
Onebrief makes military headquarters run seamlessly
391+9%+55%7$311MGrant$114K, Jul 2026
55
Organic and gourmet high-protein meals, designed for longevity.
91+8%+7%0$16.1MSeed$14M, May 2022
56
Private workspace for founders, investors, and advisors to collaborate
26+8%+4%0$125KYC investment$125K, Aug 2021
57
We make cancer care at home possible.
67+8%+24%0$60.6MSeries A$21M, Jan 2026
58
CRISPR powered Diagnostics with results in minutes.
27+8%+8%0$65MSeries A$25M, Sep 2025
59
Automated communication between hospitals and patients in Latam
41+8% 0$125KYC investment$125K, Aug 2021
60
Automated e2e screenshot testing without writing or maintaining tests
28+8%+87%YC$19.1MSeries A$15M, Jul 2026
61
Truss is a banking and payments network for blue-collar trades.
14+8%−12%1$8MUndisclosed round$3M, Apr 2026
62
One-hour antibiotic sensitivity testing
14+8%+17%0$3.6MSeed$750K, Aug 2026
63
Podium for local businesses in Latam
14+8%+8%0$125KUndisclosed round$125K, Jan 2023
64
At-home spa, beauty & grooming services marketplace for LatAm
45+7%+10%8$2.9MUndisclosed round$2.8M, Jun 2023
65
Malga is an API to accept payments with multiple payment providers
77+7%+15%0$8.4MSeries A$5.6M, Feb 2025
66
The #1 Market Network for Government Contractors.
47+7%+15%0$13.1MSeries A$9.5M, Nov 2023
67
We make instant offers to buy homes in India
142+7%+37%0$7.2MSeed$5.8M, Jun 2022
68
Whaly is building a self-service analytics platform
16+7%+33%0$2MSeed$1.9M, Jun 2022
69
Noom for Southeast Asia
68+6%+6%0$2.7MNon-equity support$2.6M, Feb 2024
70
Modernizing hedge fund back office software and services.
18+6%+6%0$3.7MSeed$3.6M, Jun 2022
71
Create, launch, and optimize Facebook ads and ads on 10+ platforms
18+6%−5%0$2.1MSeed$2M, Nov 2024
72
IP operating software for brands and content companies
289+6%+19%0$89MSeries B$48M, Sep 2025
73
Pioneering Breast Cancer Diagnostics for a Healthier Tomorrow
19+6%+6%0$261KSeed$136K, Jun 2026
74
Low-cost, high-scale EV charging platform for apartments (and more).
19+6%+6%1$7.8MGrant$3M, Feb 2026
75
A mobile app. It allows employees to get paid their salary on-demand.
84+5%−1%1$64MUndisclosed round$21.7M, Jun 2025
76
Automate finance operations with AI
22+5%+47%0$3MSeed$2.3M, Jan 2022
77
Cloud and Container Security Platform
22+5%+22%0Seed (before YC)May 2021
78
Decarbonizing the fashion industry
45+5%+10%3$17.1MSeries A$15M, Apr 2024
79
Offers insurance to customers in a convenient & transparent way
136+5%+15%0$6.7MSeed$3.3M, Nov 2024
80
Fair, simple and accessible financial services
480+4%+15%2$86.8MCorporate round$53M, May 2026
81
Remote labor for restaurants
24+4% 0$16MConvertible note$11.3M, Aug 2022
82
B2B e-commerce and fintech platform for traditional proximity stores
73+4%+3%0$21MSeries A$12M, Oct 2025
83
Simplified digital health insurance for Filipino SMBs
98+4%+11%12$6.5MSeed$6.5M, Jul 2024
84
Datlo helps companies increase sales and expand through data
50+4%−24%0$838KSeed$713K, May 2025
85
P2P Cross border payments
25+4%+14%0$14.5MSeries A$14.5M, May 2025
86
Leading wealth management and investing platform in Vietnam
51+4%+11%0$8MCorporate round$6M, Mar 2024
87
Building the human layer of AI
104+4%+33%8$64.2MSeries B$40M, Nov 2025
88
The most magical personal Voice-Led AI English Learning Buddy for Kids
82+4%+9%0$125KYC investment$125K, Mar 2022
89
Loan management software for private lenders
30+3%+76%1$13.6MSeries A$13.5M, Feb 2026
90
Operating system for insurance agencies
32+3%+10%YC
91
The fastest way to ship airtight AI
33+3%+43%0$19.3MSeries A$14.5M, May 2025
92
Track & Boost Your Brand’s Visibility in AI Search
141+3%+22%1$2.6MSeed$2.5M, Sep 2021
93
Autonomous team of AI agents that runs the entire hospital operations
71+3%−9%YC$30MUndisclosed round$21.8M, Oct 2025
94
Latin America's Deposits Marketplace for Banks
73+3%−5%0$2MSeed$1M, Apr 2025
95
Transforming Mental Health for Corporate Asia
170+2%+33%YC$2.9MSeed$2M, Feb 2022
96
AppX helps social media creators launch their own mobile apps.
129+2%+30%2$1.4MSeed$1.3M, Jan 2022
97
fluke is a full-digital mobile operator in Brazil
46+2%+18%0$1.1MNon-equity support$125K, Feb 2022
98
The platform for buying, selling and managing residential construction
50+2%+2%YC$8.6MSeed$8.4M, Oct 2021
99
Lattice for Latam with personalized learning and development
107+2%+1%0$300KSeed$300K, Oct 2024
100
Open Source Infrastructure for the Financial Internet
54+2%+10%3$30.8MSeries A$21M, Jan 2025

How this works

1. The roster

Every launched company in YC's public directory, with its batch, status, industry and location. New companies show up the week YC lists them.

2. The numbers

Each company is matched to Crustdata by its website. Crustdata adds team size and its change over 6 and 12 months, open roles from job postings, reported funding, and founders' past employers.

3. The lists

Hiring the most counts distinct roles posted in the last 60 days. Growth needs 10+ people today, shrinking 20+ a year ago, so tiny teams do not top the lists. Rebuilt every week.

Built with Crustdata. Get your own API key and build your own.

The numbers on this page come from three Crustdata API calls. Crustdata tags 5,000+ companies with Y Combinator as an investor; swap the filter for any investor, industry or headcount range and track your own list, with founders' work emails one call away.

  • Company search for team size, growth and funding
  • Job search with a count by company, for who is hiring and for what
  • A watch that re-runs the search weekly and sends only what changed
# 1. every company with Y Combinator as an investor
curl https://api.crustdata.com/company/search \
  -H "authorization: Bearer $CRUSTDATA_API_KEY" \
  -H "x-api-version: 2025-11-01" \
  -d '{
    "filters": { "field": "funding.investors",
                 "type": "in", "value": ["Y Combinator"] },
    "fields": ["basic_info.name",
      "headcount.total", "headcount.growth_percent",
      "funding.total_investment_usd"],
    "limit": 100
  }'

# 2. open listings per company, last 60 days (limit 0 = counts only)
curl https://api.crustdata.com/job/search \
  -H "authorization: Bearer $CRUSTDATA_API_KEY" \
  -H "x-api-version: 2025-11-01" \
  -d '{
  "filters": { "op": "and", "conditions": [
    { "field": "company.basic_info.company_id",
      "type": "in", "value": [...] },
    { "field": "metadata.date_added",
      "type": "=>", "value": "2026-08-24" } ]},
  "limit": 0,
  "aggregations": [{ "type": "group_by",
    "field": "company.basic_info.company_id", "agg": "count" }]
}'

# 3. the same company filter as a weekly watch: POST /watch/company/search

Questions about YC S21 companies

How many YC S21 companies are there?

390 companies were in Y Combinator's Summer 2021 batch (S21); 284 are active.

Which YC S21 companies are hiring?

50 companies posted roles in the last 60 days, led by Stepful (36 roles), Exa (28 roles) and ARQ (24 roles). 85 mark themselves as hiring on YC's directory.

Which YC S21 companies are growing fastest?

By team growth over 6 months (10+ people): Hirebolt (+100%), Aqua (+93%) and Confido (+89%).

Which YC S21 companies raised the most?

Largest latest rounds in the last 12 months, after their YC batch: Exa ($250M), Slash ($100M) and Turion Space ($75M).

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