Hongyuan Mei

I train computers to reason about the world.

Currently, I am a Member of Technical Staff in the Reasoning Team of xAI, leading the AI Experts Team. My team and I have made core contributions to Grok reasoning models, including Grok 4, Grok 4 Heavy, and Grok 4.1 Fast. We have improved Grok’s capabilities to

• reason with expert knowledge, achieving state-of-the-art performance on Humanity’s Last Exam.
• handle files (e.g., PDF, Excel) in grok.com and Grok for Business.
• call tools and follow instructions, reaching top of τ² Bench.

Before joining xAI, I was a Senior Research Scientist at Google DeepMind. Before DeepMind, I was a Research Assistant Professor at Toyota Technological Institute at Chicago (TTIC), a research institute affiliated with University of Chicago. At TTIC, I led the River Lab, conducting research on AI reasoning and planning.

I received PhD in Computer Science from Johns Hopkins University, advised by Jason Eisner. We developed the neural Hawkes process, a model widely used in event sequence modeling and prediction.