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Yi-Hang Chen

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Jul 2026

When Should Active RAG Retrieve? A Budget-Aware Evaluation of Utility, Calibration, and Cost

Active RAG systems decide when to retrieve external knowledge during generation, making them a budget-sensitive case of agentic RAG and self-adaptive retrieval. Yet evaluations often leave the operating point underspecified: two systems may both claim a 50% evidence-usage budget while realizing different held-out usage rates, so higher accuracy can reflect a looser budget rather than a better retrieval policy. We study budget-aware evaluation for Active RAG by recasting active retrieval as utility estimation, where retrieval is valuable only through its marginal correctness change over a no-retrieval answer. This view separates three questions that single-point evaluations conflate: whether trigger scores rank useful retrieval decisions, whether thresholds calibrated on past data meet future budgets, and how trigger-side computation changes deployment cost. We operationalize these questions with exact top-k utility frontiers, deployable threshold frontiers, conservative budget frontiers, harm audits, and cost decompositions. Across knowledge-intensive multi-hop QA datasets and open instruction models, retrieval harm is non-negligible, router rankings change across datasets and budgets, nominal thresholds can miss target usage, and simple uncertainty or retrieval-score baselines often rival learned utility routers. Budget-aware Active RAG evaluations should therefore report frontiers, realized usage, threshold-transfer error, harm rates, and cost decompositions alongside accuracy.

Pinyan Qian, Su Wang, Chong Peng et al. · 1 citation
Preprint Aug 2026

BAP-SQL: Budget-Aware Observation Planning for Agentic Text-to-SQL

Tool-using agents do not merely consume observations: their actions determine what arrives next. In agentic text-to-SQL, a broad query can spend context and database work before useful evidence appears, while post-hoc compression cannot recover omitted rows or expended work. We present BAP-SQL, which treats observation formation as a budget-control stage: it estimates query risk, rewrites SQL when useful, and delegates hard limits to an independent runtime shield. Across general 4B, specialized FINER-SQL 4B, and 7B backbones, BAP-SQL improves tight-budget success. On the primary BIRD-derived setting, it gains 3.4/3.6 percentage points over matched SFT while using 4.5/5.0% fewer tokens. Matched retraining and task-level transfer associate the gain with policy-visible planning and budget-sensitive rescue. The benefit attenuates as model capability and budget increase, reverses at the loosest setting, and does not reduce database work.

Chong Peng, Pinyan Qian, Su Wang et al. · 2 citations
#artificial intelligence Preprint Sep 2026

Bilevel Coordinated Reflection: A Game-Theoretic Approach to Multi-Agent LLM Systems

Multi-agent LLM systems commonly use an orchestrator to decompose a task for a team of workers and then improve through textual reflection. Despite strong empirical results, these systems lack a unified account of coordination, memory improvement, and the role of external verification. We model orchestrator-worker interaction as a bilevel coordination game: under bounded coupling, the workers'local-update game is an approximate potential game whose equilibrium slack is controlled by decomposition quality. We then analyse reflection as stochastic movement over semantic memory states. For free-form reflection, we derive a finite-time upper bound, prove worst-case tightness, and give a positive lower bound under a falsifiable persistent-harm condition. We further prove an information-theoretic impossibility result: no gate that observes only the generated transcript can improve uniformly over text-indistinguishable environments, whereas an environment-grounded gate can. Motivated by this separation, we introduce Stochastic Reflective Memory Ascent (SRMA), which accepts a candidate memory only after a grounded evaluation risk strictly decreases. Under calibration and non-degenerate corrective mass, SRMA converges exactly, geometrically or polynomially; matching constructions show that both rate regimes are order-tight. We also provide confidence gating for stochastic evaluation and re-anchoring guarantees for piecewise-stationary environments. Experiments instantiate these objects with environment-grounded metrics and test the predicted coordination and drift laws. On 500 SWE-bench instances, the complete Kimi-based system resolves 72.2% versus a 70.8% public mini-SWE-agent reference. Code: https://github.com/YihangChen9/Bilevel-Coordinated-Reflection

Yihang Chen, Yu-Xiang Chen, Yuxuan Huang et al. · 0 citations
Jul 2026

Phantom Guardrails: When Self-Improving Agent Harnesses Fix Failures That Never Happened

This work introduces the Counterfactual Fabrication Lab, a deterministic micro-lab where the correct action is known: do nothing, and presents the Counterfactual Fabrication Lab for measuring fabricated failures in self-improving agent harnesses.

Su Wang, Pinyan Qian, Yifan Lin et al. · 6 citations · ⚡2
#machine learning Preprint Aug 2026

Large Discovery Models: Empirically-grounded Model-Based Open-Ended Search

This work introduces the Large Discovery Model (LDM), an empirically grounded recurrent architecture that couples a generative model with a Bayesian non-parametric reward surrogate model, yielding an uncertainty-aware value that guides candidate generation, refinement, and selection.

Zhongwei Yu, Yan Song, Xue Yan et al. · 0 citations
Preprint Aug 2026

Explicit State Elicitation Is Not Enough: A Controlled Audit of Memory-Policy Classification

Family-level and seed-stability analyses show that example-level accuracy overstates counterfactual consistency: complete four-way family success is rare, and an exploratory follow-up that elicits decomposed semantic evidence fails to improve routing for the cleanly evaluated endpoint.

Yihang Chen, Pinyan Qian, Su Wang et al. · 0 citations
Preprint Jul 2026

Toward User-Conditioned Evaluation of Personal LLM Agents under Temporal Interventions

A minimal benchmark design and candidate reporting metrics for user-conditioned adaptation are proposed and a concrete design requirement for future personal-agent evaluation, with metrics used as reporting tools for that requirement.

Pinyan Qian, Su Wang, Yihang Chen et al. · 2 citations

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