Han Fang is a Research Lead in Core LLM at Meta’s AI Frontier org. In 2023-2024, He launched Llama 2 & 3 on Meta AI into Meta’s family of apps, growing it to 1B monthly active users. In 2025, he focuses on teaching models to think and reason (becoming agents) and more broadly post training. ​

Han holds a PhD in Applied Mathematics and has published in top-tier venues with 7500+ citations. He is a recipient of the President’s Award to Distinguished Doctoral Students, the Woo-Jong Kim Dissertation Award, and the Excellence in Research Award.

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Selected Recent Projects

• Learning Auxiliary Tasks Improves Reference-Free Hallucination Detection in Open-Domain Long-Form Generation
  Chengwei Qin, Wenxuan Zhou, Karthik Abinav Sankararaman, Nanshu Wang, Tengyu Xu, Alexander Radovic, Eryk Helenowski, Arya Talebzadeh, Aditya Tayade, Sinong Wang, Shafiq Joty, Han Fang, Hao Ma · ACL 2025

• Think Smarter not Harder: Adaptive Reasoning with Inference Aware Optimization
  Zishun Yu, Tengyu Xu, Di Jin, Karthik Abinav Sankararaman, Yun He, Wenxuan Zhou, Zhouhao Zeng, Eryk Helenowski, Chen Zhu, Sinong Wang, Hao Ma, Han Fang · ICML 2025

• Multi-IF: Benchmarking LLMs on Multi-Turn and Multilingual Instructions Following
  Yun He, Di Jin, Chaoqi Wang, Chloe Bi, Karishma Mandyam, Hejia Zhang, Chen Zhu, Ning Li, Tengyu Xu, Hongjiang Lv, Shruti Bhosale, Chenguang Zhu, Karthik Abinav Sankararaman, Eryk Helenowski, Melanie Kambadur, Aditya Tayade, Hao Ma, Han Fang, Sinong Wang · arXiv 2024

• The perfect blend: Redefining RLHF with mixture of judges
  Tengyu Xu, Eryk Helenowski, Karthik Abinav Sankararaman, Di Jin, Kaiyan Peng, Eric Han, Shaoliang Nie, Chen Zhu, Hejia Zhang, Wenxuan Zhou, Zhouhao Zeng, Yun He, Karishma Mandyam, Arya Talabzadeh, Madian Khabsa, Gabriel Cohen, Yuandong Tian, Hao Ma, Sinong Wang, Han Fang · arXiv 2024

• Launched Llama 3 on Meta AI and subsequently Llama 3.1.
  Meta AI Blog Post

• Launched Llama 2 on Meta AI.
  My talk at Meta’s Connect Conference in 2023