Case study · Aug 11, 2026
Democratizing mentorship via AI Digital Twins
Y Combinator chose LemonSlice to power its interactive avatar experience called the Office Hours Simulator.
“The LemonSlice avatars are so realistic that you forget you're not talking to a human.”
Jared Friedman · General Partner at YCCompany: Y Combinator
Region: North America, Global
Use Case: Digital Twins
9 min
median conversation
(out of a 10min limit)
Many
forgot they were
talking to AI
81%
had a valuable
conversation
The Problem
For 20 years, Y Combinator (YC) has helped startups ranging from Airbnb, Stripe, Instacart, and Reddit get off the ground. YC's mission is to create more startups in the world. The problem is that there are more great founders than YC has the resources to help.
One of the most impactful things YC does, for example, is give personalized mentorship through 1-on-1 conversations called Office Hours, which is difficult to scale. But advances in AI have made it possible to democratize many new experiences and YC pushed themselves to explore the question: “Can AI help democratize the Office Hours experience while still maintaining quality?”
It turned out the resulting product was more successful — and the results more surprising — than YC could have predicted.
“The LemonSlice experience is magical.”
The Solution
YC built digital twins of the YC Partners using LemonSlice. These digital twins are AI avatars of their real human counterparts that can have personalized, 1-on-1 conversations with founders. The avatars are featured in both web and physical product experiences.
The brains for each avatar is controlled by an LLM with custom prompting and a custom knowledge base that is distilled from data of how the real person asks questions and approaches problems. The avatars also have full access to YC's 20-year accumulated library of startup advice and knowledge. The physical appearance — the face, body, and setting — of the avatars is powered by LemonSlice's Character World Model (CWM). LemonSlice works off a single image in any style. Therefore AI image tools were used to design each YC Partner's appearance to show off a part of their personality.
Additional tools include Deepgram for the STT, ElevenLabs for the voice, LiveKit for the agent orchestration, and Ploy for the animation creation.
The Office Hours Simulator
Here is a video of the physical booths in action at YC Startup School:
The web version of the Office Hours Simulator allows users to choose from a variety of “modes” ranging from Office Hours to Practice YC Interviews.
Why Add a Face?
YC could have built this just as a chat or voice UI, but their early testing indicated that people behaved differently with a face.
“The face adds an empathy part. There's something about seeing a face talking to you that causes people to open up and trust more. They treat [the product] less like a tool and more like a real person.”
Jared Friedman · General Partner, Y CombinatorThe Results
YC's Digital Twins were a huge hit across both the web and physical experiences. The most surprising thing to YC was how deep and meaningful the conversations were; they went beyond tactical advice and into emotional questions and struggles like rocky co-founder relationships and feeling burned out.
01
People forgot it was AI
People repeatedly reported that they forgot they were talking to AI. 24% of founders said "thank you." At the physical booths, people were leaning in, taking notes, and gesticulating while talking. Users said the face-to-face experience made them feel "more comfortable" and "engaged."
“It was very lifelike. You actually forget that you're talking to AI.”
Rasmus HauschildFounder and CTO, AIRY02
The conversations were actually helpful
People were seen scribbling notes on pen and paper or whipping out their Granola notetakers on their phones. Many were caught off guard by how helpful the conversations were. 81% of YC founders had a valuable conversation. And even founders who've raised $100M+ reported having real GTM unlocks via their avatar conversation.
“I went in half joking but literally 2 turns of conversation in I was fully having an office hour. It was so good!”
Siamak FreydoonnejadYC Founder W2203
People wanted more of it
The #1 complaint at YC Startup School is that the conversations were too short (since there was an enforced 10-minute time limit). There was a continual line of people for the entire 2-day conference. People stood in line multiple times to have more conversations. Web users had 30-40 minute-long conversations and then came back for another 30-minutes the next day. They asked for features to give the avatars even more context so responses could be even more personalized.
Very lifelike
“It was very lifelike. [The face-to-face] helps get the connection. You actually forget that you're talking to AI.”
Rasmus Hauschild
Founder and CTO, AIRY
Credible and engaging
“It felt a lot more credible to see a person's face. All the live feedback of them reacting and listening to you in real-time made it more engaging.”
Nitya
Berkeley student
More approachable
“Seeing the human face in front of you makes it more real and more approachable. We're humans and we like to see the human face.”
Mickael Naouri
Stanford student
The Office Hours Simulators are living on. Corgi, a YC company running 24/7 founder cafés across the US and UK, is installing the Office Hours Simulators in its locations — putting always-on AI office hours in cities around the world. Another Simulator will live in the YC Headquarters in San Francisco. And the web version is expanding beyond just access to YC founders. YC is excited about the potential to scale themselves and help more founders.
Why LemonSlice?
“Building with LemonSlice was the easiest part of the whole stack. It just works.”
Jared Friedman · General Partner, Y Combinator01
It's highly lifelike
LemonSlice is not just a talking head model. It's a full Character World Model, and so the entire scene, not just the avatar, moves naturally. This creates a really immersive experience.
02
It's easy to build with
YC shipped a V1 prototype with LemonSlice in one day. And then had that same system scale to hundreds of daily conversations across web and physical installations without any problems.
03
It can be paired with an advanced AI brain
LemonSlice's API-first design works seamlessly with any LLM, knowledge base and tool calls. This was critical to YC because they wanted full control over the brains.
“If you want your users to have a real connection to your AI, adding a face is a no-brainer — and LemonSlice is the easiest way to do it.”
Jared Friedman · General Partner, Y Combinator
