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14,448 startups · 29 programs

TrainLoop

Active · Reasoning Fine-Tuning

WebsiteYC profile

Why it ranks

How the rank works
10signal of 100 · rising 6
  • team of 6Team size · YC's directory+4.4
  • went through YCProgram · this site+4
  • hiringHiring · Titles (titles.fru.dev), YC+2

A sum of public facts, not a judgement and not investment advice.

Competitors

AIUnsloth AIShared: fine tuning, reinforcement learningYC S24San FranciscoStartup →AITagflow AIShared: fine tuning, llmAntler 2024IndonesiaStartup →AIOsmosisShared: reinforcement learning, fine, performanceYC W25San FranciscoStartup →AICartpoleShared: reinforcement learningYC X25San FranciscoStartup →AIZorbeShared: fine tuning, reinforcement learningspeedrun SR007San FranciscoStartup →OtherTogether AIShared: fine tuningStartup →OtherPrime IntellectShared: reinforcement learningStartup →
Companies closest to TrainLoop
Company
Unsloth AIShared: fine tuning, reinforcement learningYC S24ActiveAI, Devtools
Tagflow AIShared: fine tuning, llmAntler 2024Not statedAI
OsmosisShared: reinforcement learning, fine, performanceYC W25ActiveAI, Devtools
CartpoleShared: reinforcement learningYC X25ActiveAI, Data
ZorbeShared: fine tuning, reinforcement learningspeedrun SR007Not statedAI, Data
Together AInot in a program hereShared: fine tuningElsewhereOther
Prime Intellectnot in a program hereShared: reinforcement learningElsewhereOther

Adjacent

Developer toolsVmaxShared: reinforcement learningSPC 2025San FranciscoStartup →AIZibra LabsShared: fine tuning, reinforcement learning, performanceYC X26San FranciscoStartup →AIDatacurveShared: fine tuningYC W24San FranciscoStartup →AIInactiveAirtrain AIShared: fine tuning, llmYC S22San FranciscoStartup →Developer toolsPreference ModelShared: reinforcement learningSPC 2025San FranciscoStartup →
Companies next to TrainLoop
Company
VmaxShared: reinforcement learningSPC 2025Not statedDevtools
Zibra LabsShared: fine tuning, reinforcement learning, performanceYC X26ActiveAI, Devtools
DatacurveShared: fine tuningYC W24ActiveAI
Airtrain AIShared: fine tuning, llmYC S22InactiveAI, Devtools
Preference ModelShared: reinforcement learningSPC 2025Not statedDevtools

Also from W25 in AI

All of W25
AIa0.devWe make mobile apps using AI.YC W25San FranciscoStartup →AIAgentin AIFoundational model researchYC W25San FranciscoStartup →AIArtilLet your agents message teammates and other agentsYC W25LondonStartup →AIassistant-uiOpen Source React.js Library for AI ChatYC W25San FranciscoStartup →AICodevisorThe fastest native app for agentic engineering.YC W25San FranciscoStartup →AIConfident AIProduction Monitoring & Evals for AI AgentsYC W25San FranciscoStartup →
Company
a0.devWe make mobile apps using AI.team of 3hiringActiveAI, Devtools
Agentin AIFoundational model researchteam of 2ActiveAI
ArtilLet your agents message teammates and other agentsteam of 2ActiveAI, Devtools
assistant-uiOpen Source React.js Library for AI Chatteam of 3ActiveAI, Devtools
CodevisorThe fastest native app for agentic engineering.team of 2ActiveAI, Devtools
Confident AIProduction Monitoring & Evals for AI Agentsteam of 7hiringActiveAI, Devtools

Founders

  • Jackson StokesFounder/CEO
  • Mason PierceFounder/CTO

About TrainLoop

TrainLoop makes it effortless for developers to supercharge LLM performance through reinforcement learning.

YC batch
W25 · Winter 2025
Status, per YC
Active
Category
AI, Developer tools
Team size
6
Location
San Francisco, CA, USA
Founded
2025
Checked
6h ago

YC tags: Developer Tools, Generative AI, Reinforcement Learning

Changes seen

HiringOct 15, 2026

Started hiring.

Source ↗

TrainLoop in W25: 166 companies, 84% AI

GitHub LinkedIn

TrainLoop: questions

Which YC batch was TrainLoop in?

TrainLoop was in Y Combinator's Winter 2025 batch (W25).

Is TrainLoop still active?

Y Combinator lists TrainLoop as active.

Who founded TrainLoop?

TrainLoop's founders, as listed on its YC page: Jackson Stokes (Founder/CEO), Mason Pierce (Founder/CTO).

Where is TrainLoop based?

TrainLoop lists San Francisco, CA, USA as its location on YC's directory.