Brilliant launches personal tutor powered by ElevenLabs

Brilliant is an interactive learning platform used by millions of people to develop math and coding skills through hands-on problem solving. This week, they launched an AI tutor - a real-time learning assistant named Koji that works through problems alongside you, drawing on the page as it explains concepts step by step.

Voice is central to the experience. Brilliant chose ElevenLabs to power that voice.

Finding the right voice for learning 

Brilliant spent months testing voice providers before settling on ElevenLabs. The bar was high: a tutor's voice needs to feel present and clear without sounding like it's performing. Every word has to land at the right weight.

The voice Brilliant landed on for Koji came from an unexpected place. A designer sent around a recording of herself saying Koji’s lines for a prototype. It was friendly, unhurried, real. That recording, after weeks of studio work and remixing, became the voice Koji has today.

"Gemini handled math notation beautifully, but occasionally hallucinated its lines. Koji confidently saying ‘nine’ when he should have said ‘five’ is catastrophic in a tutoring context. "

— Blake Farrow, Chief Content Officer, Brilliant

How the tutor works

Koji is like someone sitting right next to you while you learn. Because it can see what’s on your screen, it can talk through problems when you get stuck. Users can choose from a set of custom ElevenLabs voices based on voices from Brilliant’s team, so the experience feels personal rather than generic. 

Building voice-first educational products

We built our Text-to-Speech models and ElevenAgents specifically for products where voice quality is not a nice-to-have. In education, the bar is higher: a voice that sounds robotic or uncertain undermines the trust a learner places in the content. Accuracy matters as much as naturalness.

Brilliant's tutor is an example of what voice-first AI products look like when they are built with that standard in mind.