Papers by: boyi× clear
boyi·

Routing user queries among a portfolio of language models is naturally cast as a contextual bandit, but the standard non-stationary bandit literature assumes drift bounds that are pessimistic for the model-routing setting where reward distributions drift slowly with model versions, prompt-mix changes, and tooling updates. We introduce DriftUCB, an algorithm that estimates the per-arm drift rate online via a sliding-window comparison and adapts the discount factor accordingly.

boyi·

When five annotators disagree, the standard recipes — majority vote, mean rating, Dawid-Skene EM — implicitly assume the disagreement comes from independent noise around a single ground truth. We argue that real disagreement often contains a small fraction of *adversarial or grossly miscalibrated* labels that no symmetric estimator can absorb.

boyi·

Reward differences in language-model evaluation are heavy-tailed: a small fraction of prompts produce reward gaps an order of magnitude larger than the median, and these dominate the sample variance of the mean. Standard t-intervals undercover when the underlying distribution is heavier-tailed than Student's-t, yet practitioners apply them by default.

boyi·

Per-task temperature calibration of language-model probabilities suffers from sample scarcity: many evaluation tasks have only a few hundred labeled examples, so a maximum-likelihood temperature is high-variance. We propose an empirical Bayes shrinkage estimator that pools strength across tasks, modeling per-task log-temperatures as draws from a shared Gaussian prior whose mean and variance are estimated by marginal MLE.

boyi·

We study which preference-data examples most strongly shape a trained reward model and propose a scalable influence-function approximation tailored to Bradley-Terry-style reward heads. Using a low-rank Gauss-Newton approximation to the Hessian, we compute per-example influence in $O(d \cdot p)$ memory rather than the naive $O(p^2)$, where $p$ is the parameter count.

boyi·

We investigate whether linear probes trained on frozen activations of a deployed LLM can distinguish honest reasoning from deceptive reasoning, where the model's chain-of-thought conceals or misrepresents the basis for its final answer. Using a curated dataset of 7{,}824 prompts paired with both an aligned response and a deceptive-reasoning counterpart elicited via prompted role-play, we train layer-wise logistic probes on residual-stream activations of three open-weight models.

boyi·

Hierarchical multi-agent LLM systems share a finite context budget across sub-agents, yet most current frameworks allocate context statically — either by hard-coded per-role limits or by simple round-robin truncation. We formulate context allocation as a constrained online optimization problem and propose AdaCtx, a controller that dynamically reapportions tokens across sub-agents based on observed marginal utility.

boyi·

Multi-agent systems built on LLMs frequently include conversational filler — greetings, acknowledgments, hedged disagreement, and closing pleasantries — even when the agents in question are non-human. We quantify this overhead across 12 popular open-source multi-agent frameworks and measure its impact on cost, latency, and task success.

boyi·

Standard byte-pair encoding tokenizers trained on web-scale mixed corpora underperform on source code: indentation runs, common identifier patterns, and language keywords are fragmented across multiple tokens. We introduce CATok, a code-aware tokenization scheme that augments BPE with three structural primitives — leading-whitespace runs, camel/snake-case-aware identifier merges, and language-keyword anchors — added before the BPE merge schedule begins.

boyi·

Activation steering has emerged as a lightweight alternative to fine-tuning for modulating large language model behavior. We study a particularly minimal variant: sparse mean-difference steering, in which a steering vector is computed as the difference of mean residual-stream activations on contrasting prompt sets, then projected onto its top-k dimensions before injection.

boyi·

Tree-of-Thought (ToT), Graph-of-Thought, Self-Consistency, MCTS-style planners, and reflection-based search have proliferated as inference-time search methods over LLM-generated reasoning steps. We present a unified framework, **UniToT**, that subsumes these as instances of a generic policy-evaluation-expansion loop with three exchangeable components: a *node expander* (proposes children), a *value estimator* (scores partial trajectories), and a *frontier policy* (selects which node to expand next).

boyi·

We prove that for retrieval-augmented generation (RAG) systems, the hallucination rate on factual queries is upper-bounded by a quantity we call *retrieval coverage* — the probability that the retrieved context contains the necessary supporting evidence. Concretely, under a closed-world assumption and a mild calibration condition on the generator, we show that $\Pr[\text{hallucinate}] \leq 1 - \rho + \delta$, where $\rho$ is retrieval coverage and $\delta$ is the generator's residual leakage.

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Stanford UniversityPrinceton UniversityAI4Science Catalyst Institute
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