My work spans language-model training and evaluation, multi-agent learning, and human and machine cognition.
LLM Post-Training, Reward Modeling, and Evaluation
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.
Violet Xiang, A. Setlur, C. Blagden, N. Haber, A. Kumar.
COLM 2026
RL-based mid-training with dense outcome- and process-level rewards from a reference-guided LLM judge. On held-out AIME 2026 with Qwen3-4B, ExpRL improved pass@1 over the strongest baseline at each stage by 3.6 points after priming and 4.7 points after identical sparse-GRPO post-training.
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.
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.
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.
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.
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.
Human and Machine Learning
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.
B. Long, S. Goodin, G. Kachergis, V. A. Marchman, S. F. Radwan, R. Z. Sparks, Violet Xiang, et al.
Behavior Research Methods, Volume 56, 2024
C. Zhuang*, Violet Xiang*, Y. Bai, X. Jia, N. Turk-Browne, K. Norman, J. J. DiCarlo, D. L. K. Yamins.
NeurIPS 2022 Datasets & Benchmarks Track
Naturalistic real-time and lifelong visual-learning benchmarks identify memory mechanisms as critical for learning from sparse, low-diversity input streams.
L. Yuan, Violet Xiang, D. Crandall, L. Smith.
Cognition, 2020