Publications

My work spans language-model training and evaluation, multi-agent learning, and human and machine cognition.

* indicates equal contribution. See also Google Scholar.

LLM Post-Training, Reward Modeling, and Evaluation

Test-Time Self Improvement by Scaling Unsupervised World Internalization

Violet Xiang, M. Khalifa, I. Wu, Y. Shen, J. Leskovec, N. Haber, A. Kumar.

Under review at ICLR 2027

U-WIN enables agents to explore new environments and train on self-written notes and self-generated trajectories without access to downstream tasks, rewards, or correctness feedback. Across legal, codebase, and math environments, downstream performance improved near log-linearly as training scaled from 10M to 100M tokens.

One Bias After Another: Mechanistic Reward Shaping and Persistent Biases in Language Reward Models

D. Fein*, M. Lamparth*, Violet Xiang, M. J. Kochenderfer, N. Haber.

ICML 2026

Identified persistent length, uncertainty, position, sycophancy, and model-style biases in language reward models. Null-space probe projections reduced three of these biases without retraining or loss on RewardBench-2.

LitBench: A Benchmark and Dataset for Reliable Evaluation of Creative Writing

D. Fein*, S. Russo*, Violet Xiang*, K. Jolly, R. Rafailov, N. Haber.

EACL 2026 · Long Paper

A creative-writing evaluation benchmark with 43k training pairs and a 2.5k-pair debiased, human-labeled test set. Trained reward models improved human-preference agreement by 5 points over the strongest zero-shot judge.

Just Enough Thinking: Efficient Reasoning with Adaptive Length Penalties Reinforcement Learning

Violet Xiang, C. Blagden, R. Rafailov, N. Lile, S. Truong, C. Finn, N. Haber.

NeurIPS 2025 Efficient Reasoning Workshop · Spotlight

A GRPO-compatible adaptive length penalty reduced DeepScaleR-1.5B generation length by more than 50% at matched accuracy across MATH-500, AIME, and OlympiadBench, while allocating 5.35× more tokens to hard prompts than easy ones.

ResearchCodeBench: Benchmarking LLMs on Implementing Novel Machine Learning Research Code

T. Hua, H. Hua, Violet Xiang, B. Klieger, S. Truong, W. Liang, F.-Y. Sun, N. Haber.

NeurIPS 2025 Datasets & Benchmarks Track · Spotlight

An execution harness for 212 research-code challenges from 20 recent ML papers. Across 32 evaluated models, the strongest reached 33.0% on the HARD split, and 43 tasks remained unsolved by every model.

Towards System 2 Reasoning in LLMs: Learning How to Think With Meta Chain-of-Thought

Violet Xiang, C. Snell, K. Gandhi, A. Albalak, A. Singh, C. Blagden, D. Phung, R. Rafailov, N. Lile, D. Mahan, L. Castricato, J.-P. Fränken, N. Haber, C. Finn.

Preprint, 2025

A training roadmap combining linearized search traces, process supervision, synthetic data, and reinforcement learning, supported by evidence of in-context search behavior in frontier reasoning models.

Multi-Agent Learning

Human and Machine Learning

The BabyView Dataset: High-Resolution Egocentric Videos of Infants’ and Young Children’s Everyday Experiences

B. Long*, R. Sparks*, Violet Xiang*, S. Stojanov*, et al.

Computational Cognitive Neuroscience 2025 Proceedings

An 868-hour longitudinal egocentric-video dataset spanning ages 5 months to 3 years, with annotations and evaluation pipelines for speech transcription, diarization, pose estimation, and out-of-distribution transfer.

Privacy and Security

Earlier Work