Justin Lidard

I am a Research Scientist at Google DeepMind, where I build generally capable robots that act safely in the real world. I currently focus on training robot policies from video data.

I recently completed my PhD at Princeton, where I worked with Anirudha Majumdar and Naomi Leonard on robotics. During my PhD, I worked on RL for diffusion policies, safety filters, and dynamic games. Along the way, I spent time at the Toyota Research Institute working on human-interactive driving, and at Google DeepMind with Vikas Sindhwani.

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For an up-to-date list, see my Google Scholar.

Reasoning About Uncertainty: Do Reasoning Models Know When They Don't Know?

Zhiting Mei, Christina Zhang, Tenny Yin, Justin Lidard, Ola Shorinwa, Anirudha Majumdar
Findings of the Association for Computational Linguistics (EACL) 2026
TL;DR: We introduce a benchmark testing whether reasoning models know what they don't know, and find that longer chains of reasoning tend to make them more overconfident.
Webpage • PDF

Safety with Agency: Human-Centered Safety Filter with Application to AI-Assisted Motorsports

Donggeon David Oh, Justin Lidard, Haimin Hu, Himani Sinhmar, Elle Lazarski, Deepak Gopinath, Emily Sumner, Jonathan DeCastro, Guy Rosman, Naomi Leonard, Jaime Fernández Fisac
Robotics: Science and Systems (RSS) 2025
TL;DR: We introduce a neural safety filter that overrides a human driver as little as possible while still keeping them safe, validated in AI-assisted racing.
Webpage • PDF

Diffusion Policy Policy Optimization

Allen Z. Ren, Justin Lidard, Lars L. Ankile, Anthony Simeonov, Pulkit Agrawal, Anirudha Majumdar, Benjamin Burchfiel, Hongkai Dai, Max Simchowitz
International Conference on Learning Representations (ICLR) 2025
TL;DR: We introduce DPPO, which fine-tunes diffusion policies with policy gradients to reach state-of-the-art performance on robot manipulation.
Webpage • PDF • Code

Guiding Data Collection via Factored Scaling Curves

Lihan Zha, Apurva Badithela, Michael Zhang, Justin Lidard, Jeremy Bao, Emily Zhou, David Snyder, Allen Z. Ren, Dhruv Shah, Anirudha Majumdar
arXiv preprint, 2025
TL;DR: We introduce factored scaling curves that predict how much each environment factor limits a policy, showing where to spend a data-collection budget.
Webpage • PDF • Code • Video

A Survey on Uncertainty Quantification of Large Language Models: Taxonomy, Open Research Challenges, and Future Directions

Ola Shorinwa, Zhiting Mei, Justin Lidard, Allen Z. Ren, Anirudha Majumdar
ACM Computing Surveys, 2025
TL;DR: We survey the landscape of uncertainty quantification for large language models and organize it into a single taxonomy.
PDF

Blending Data-Driven Priors in Dynamic Games

Justin Lidard, Haimin Hu, Asher Hancock, Zixu Zhang, Albert Gimó Contreras, Vikash Modi, Jonathan DeCastro, Deepak Gopinath, Guy Rosman, Naomi Leonard, María Santos, Jaime Fernández Fisac
Robotics: Science and Systems (RSS) 2024
TL;DR: We introduce KLGame, a dynamic game that pulls a learned reference policy toward game-theoretic equilibria to capture how people actually drive.
Webpage • PDF • Code

Risk-Calibrated Human-Robot Interaction via Set-Valued Intent Prediction

Justin Lidard, Hang Pham, Ariel Bachman, Bryan Boateng, Anirudha Majumdar
Robotics: Science and Systems (RSS) 2024
TL;DR: We introduce RCIP, which predicts a calibrated set of plausible human intents so a robot knows when to act and when to ask for help.
Webpage • PDF • Code

Provably Efficient Multi-Agent Reinforcement Learning with Fully Decentralized Communication

Justin Lidard, Udari Madhushani, Naomi Ehrich Leonard
American Control Conference (ACC) 2022
TL;DR: We introduce a decentralized multi-agent RL algorithm where agents share information only with neighbors, and prove it converges faster as the group grows.
PDF • IEEE

2026

Joined Google DeepMind as a Research Scientist!

Defended my PhD thesis.

Gave talks at Google and TRI.

2025

Started as a Student Researcher at Google DeepMind, working on whole-body control.

2022

Awarded the NSF Graduate Research Fellowship.

2020

Fortunate to be awarded the National Defense Science & Engineering Graduate Fellowship (NDSEG) and the NASA Space Technology Research Fellowship (NSTRF).