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Jon Xu

Verified account Y Combinator

@xuster

General Partner @YCombinator, Co-Founder @FutureAdvisor (YC S10), MIT EECS
San Francisco, CA Joined June 2007
381 Following 4.1K Followers 403 Posts

Latest posts 5

Jon Xu Verified account @xuster
So pumped to work with Vivian and Raphael! Excited for the founders that get to partner with them.
Y Combinator Verified account @ycombinator Oct 1
We’re excited to welcome @vivianmshen and @raphaelschaad as YC’s newest General Partners!

Vivian and Raphael first came to YC as founders.

Vivian co-founded Juni Learning (W18), which teaches kids coding and math, and later founded Acely, an AI tutor for college prep. Raphael founded Cron (W20), the calendar app that became Notion Calendar.

They built products used by millions of people, then returned to YC as Visiting Partners to help other founders. Now they're doing it full-time.

ycombinator.com/blog/welcome-v…
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Jon Xu Verified account @xuster
Fresh off their Series A announcement, @Jerr_Wu and @wgm752 from @HalluminateAI joined me to discuss the future of post-training, simulating entire companies, and why alignment and safety start with the environments models learn in. Really enjoyed their perspective from building at the frontier of model training.
Y Combinator Verified account @ycombinator Oct 1
Halluminate is building reinforcement learning environments and benchmarks to help AI models do knowledge work beyond coding, starting with finance.

With a team of fewer than 10 people, the company works with four of the top five closed-source US AI labs and recently raised a $30M Series A.

In this fireside, co-founders @Jerr_Wu and @wgm752 sit down with YC's @xuster to share how testing browser agents led them to building the environments models now use to practice tasks like financial modeling. They explain why better verification, not just more training tasks, is critical to making models smarter, and how that work could eventually lead to simulated companies where teams of AI agents learn to work together.

00:00 — Halluminate’s Pivot From Evals to Training Environments
03:48 — Teaching AI to Do Financial Work
07:13 — Why Verification Matters More Than Volume
10:13 — From Finance to Simulated Companies
13:30 — AI Safety and Building the Team
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Jon Xu Verified account @xuster
@Jerr_Wu and @wgm752 have built one of the fastest growing companies out of YC Summer 25 batch.@HalluminateAI is defining the core training infrastructure for how frontier models get smarter. Very excited for what's coming next from them. Congrats on the Series A! 🚀
Jerry Wu Verified account @Jerr_Wu Oct 1
Today we're excited to announce @HalluminateAI's $30M Series A led by @oakhcft with participation from @YCombinator, @orangecollectv, @FTPartners, @heavybit, and more.
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Jon Xu Verified account @xuster
Congrats to @TungaBayrak and the @FreyaVoice team on launching the most human-like AI voice model.
Tunga Bayrak Verified account @TungaBayrak Sep 21
Today we’re releasing Adam and Eve, the most human-like AI voices ever built.

Adam ranks #1 among AI models on @DesignArena’s AudioRealismBench.

We believe we’ve crossed the uncanny valley. API access on our Website!

Listen: freyavoice.ai

Leaderboard: designarena.ai/leaderboard/au…

Special thanks to @alpsencerozturk, @ahmeterdempmk, and the entire Freya team for making this possible.

We’re just getting started. Join us!
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