ESS-Flow: Training-free guidance as Bayesian inference in source space
Adhithyan Kalaivanan, Zheng Zhao, Jens Sjölund, Fredrik Lindsten
AI 速览：ESS-Flow 利用流模型源分布的高斯先验，在源空间用椭圆切片采样做无梯度贝叶斯推断，实现预训练流模型的条件生成。
Guiding pretrained flow-based generative models for conditional generation or to produce samples with desired target properties enables solving diverse tasks without retraining on paired data. We present ESS-Flow, a gradient-free method that leverages the Gaussian prior of the source distribution in flow-based models to perform Bayesian inference directly in the source space using elliptical slice sampling. ESS-Flow only requires forward passes through the generative model and observation process, making it applicable even when gradients are unavailable, such as with non-differentiable simulation-based observations or quantization in the generation process. We demonstrate its effectiveness on scientific applications including generating materials with target properties, protein backbone structures with improved designability, and synthesizable, drug-like molecules.
Retrieval-Augmented Generation (RAG) has become the backbone of knowledge-intensive multi-hop question answering, yet routing every sub-query through a frontier model turns every hop into a cost multiplier and makes real-world deployment prohibitively expensive. Existing remedies either fix the retrieval schedule, route once at the query level, or lack a principled stopping rule, leaving a critical gap: no framework adapts, hop by hop, to how a trajectory actually unfolds. We introduce RAG-on-a-Diet, a lightweight reinforcement-learning agent that treats each reasoning hop as an independent decision and selects the smallest model (Qwen3-4B, Qwen3-30B, or DS-R1-671B) sufficient for it, guided by entity- and confidence-aware features. Trained via behavior cloning followed by PPO under a five-component cost-aware reward (final, cumulative, step-wise, cost, balance) and coupled with an explicit two-tier termination policy (5-hop cap plus a tau=0.3 confidence gate), the agent carves a Pareto-optimal efficiency frontier. On HotpotQA it cuts Monetary Inference Cost by 60.07% against IRCoT with only a 3.7% F1 drop; it matches Adaptive-RAG’s F1 at 37.30% lower cost; and it attains up to 2.33x higher Quality-per-Monetary-Cost. Consistent gains on MuSiQue, 2WikiMultiHopQA, CRAG, and Bamboogle confirm strong out-of-distribution robustness, setting a new paradigm for fine-grained resource control in multi-hop RAG.
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cs.CL
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers) · 2026 · 正式发表