TrainLoop YC Application

Profile updated September 9, 2026Winter 2025Active

San Francisco, CA, USA

TrainLoop went through Y Combinator in the Winter 2025 batch as a B2B company. Below: what the company does, who founded it, and its application to YC, reconstructed question by question in the real YC form.

YC batch: Winter 2025
Industry: B2BEngineering, Product and Design
Location: San Francisco, CA, USA
Team size: 6
Status: Active
Launched: 2025

Founders

Jackson StokesFounder
Mason PierceCofounder / CTO

What TrainLoop does

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

TrainLoop's YC application, reconstructed

Y Combinator application

TrainLoop, Winter 2025 batch. The real form questions, answered from public data.

Founders2
Company7
Progress7
Idea4
Equity3
Curious2
Batch Preference1

Company

Company name

TrainLoop

Describe what your company does in 50 characters or less.

Reasoning Fine-Tuning

What is your company going to make? Please describe your product and what it does or will do.

We build a platform that makes it effortless for developers to improve large language models' performance using reinforcement learning. Our tools let teams fine-tune LLMs not just on static datasets but on reasoning tasks, shaping outputs through feedback loops to get better results for their products.

Where do you live now, and where would the company be based after YC?

We live in San Francisco, and the company will remain based here after YC.

Explain your decision regarding location.

San Francisco is where our team is based, with access to a strong AI and developer ecosystem that supports our product development and hiring needs.

21 more answers in the full application

Founders, Progress, Idea, Equity, Curious, Batch Preference are in the full version. Create a free account to open it in YC Insights, next to every other YC batch.

See full application

Frequently Asked Questions

Is this the real TrainLoop YC application?

No. This is a reconstruction: the real YC form questions, answered from TrainLoop's public data (launch notes, founder backgrounds, product description). It shows how a company like TrainLoop would present itself to YC, not the text they submitted. Y Combinator does not publish most applications.