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eess.SPcs.AI Tianyi Ding, Yang Gao, Zhuang Xiong et al. · Oct 14, 2026

Partial-volume (PV) effects blur tissue boundaries in Magnetic Resonance Fingerprinting (MRF), and conventional pipelines rely on multi-stage dictionary matching or statistical segmentation that propagate errors. DeepPV-MRF proposes an end-to-end deep network that directly maps raw, aliased MRF time-series signals to voxel-wise CSF, GM, and WM fraction maps, bypassing intermediate $T_1$/$T_2$ reconstructions. On simulated data the method reports large accuracy gains over dictionary-matching and pseudoinverse baselines, but its real-world evidence rests on synthetic training labels and a small in vivo cohort without ground truth.

Background: Estimating subvoxel tissue fractions from magnetic resonance fingerprinting (MRF) is challenging. Conventional dictionary matching and segmentation pipelines can propagate errors from intermediate parametric maps into tissue fraction estimates. Purpose: We introduce DeepPV-MRF, a deep learning framework that directly estimates voxel-wise tissue fractions from raw MRF signals. Methods: A cascaded spatial-temporal network was trained on subject-derived Bloch simulations with radial k-space undersampling. The network combines temporal encoding and spatial U-Net refinement to estimate cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM) fractions without intermediate T1/T2 maps. We compared DeepPV-MRF with partial-volume dictionary matching (PV-DM) and pseudoinverse estimation (PV-Pinv) using simulated and in vivo data. Results: DeepPV-MRF outperformed both methods across acquisition settings. In single-shot simulations, CSF/WM/GM mean absolute errors were 0.0418/0.0744/0.0757, versus 0.1281/0.2443/0.2958 for PV-DM and 0.2021/0.2793/0.2630 for PV-Pinv. Corresponding structural similarity values were 0.960/0.916/0.922. In vivo results showed sharper anatomical boundaries and smoother tissue transitions, while cross-shot analysis indicated improved consistency across volunteers. Conclusions: DeepPV-MRF enables accurate and efficient direct tissue fraction estimation from MRF signals, particularly with limited shots. Further validation is needed before clinical deployment.
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cs.LGcs.AI Christos Panourgias, Roberto Stanzione, Adrien Petralia et al. · Oct 14, 2026

Model selection for time-series anomaly detection remains a critical open problem because no single detector dominates across heterogeneous datasets. This paper proposes RAMSAD, a retrieval-based framework that replaces trainable meta-learners with non-parametric similarity search over a knowledge base of past series and their detector-performance profiles. By matching new queries to previously seen instances via time-series foundation model embeddings—optionally augmented with multimodal semantic alignment—the authors argue they can achieve stronger in-distribution accuracy and out-of-distribution robustness at a fraction of the computational cost.

Anomaly detection is a fundamental task for time-series analytics, with important implications for the downstream performance of many applications. Despite the large number of anomaly detection methods proposed in the literature, recent benchmark studies have shown that no single detector performs best across highly heterogeneous time series. Therefore, a practical and scalable solution is to develop a model-selection method that, for a given time series, selects the anomaly detector most likely to perform well. Nevertheless, the model selection approaches proposed in the literature suffer from a significant drop in accuracy when applied in Out-of-Distribution (OOD) settings. In this paper, we tackle the aforementioned limitation and propose RAMSAD, a retrieval-based framework for model selection in time-series anomaly detection. Given a new time series, our method queries a knowledge base of previously observed instances, retrieves the top-k most similar series, and transfers detector recommendations from their performance profiles. The framework can operate with standard similarity measures as well as embedding-based representations. Our results show that RAMSAD outperforms existing baselines in In-Distribution (ID) settings and is the most robust selector in OOD, where, when selecting a small subset of detectors, it matches or exceeds ensembles that run the entire detector pool, at a fraction of their cost. Overall, we demonstrate that similarity-based retrieval constitutes a strong and efficient foundation for model selection in time-series anomaly detection.
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cs.CLcs.AIcs.LG Jia Tong, Senyou Deng, Min Peng et al. · Oct 14, 2026

Agent skills let frozen models adapt through editable external instructions, but optimizing them faces a tension: batching many changes obscures which edit mattered, while judging each edit only by its immediate score risks discarding useful stepping stones. AtomSearch proposes contrastive atomic editing—one primitive rule edit tied to execution evidence—and Skill-State Tree Search (STS), which tests short edit compositions and keeps a composed state only if it beats its primitive child. The hope is to find compact, inspectable skills without greedy myopia.

Agent skills adapt frozen models through editable external instructions. Revising several rules at once makes changes difficult to inspect, while judging each local edit only by its immediate score can discard useful intermediate states. We introduce AtomSearch, which keeps revision actions local while using subsequent skill states to guide search. Contrastive atomic editing links each primitive rule edit to failed and successful executions, a behavioral hypothesis, and an intended scope. Skill-State Tree Search (STS) evaluates short edit compositions and selectively retains them as executable states that can be revisited and extended. Outcome memory supplies later proposals with observed repair and regression statistics. We evaluate AtomSearch across four tasks and five target models. With deepseek-v4-flash, it exceeds SkillOpt on three of four tasks, including a 9.68-percentage-point gain on LiveMathematicianBench, and SkillOpt's final skills contain 2.3-19.7 times as many characters. In 67% of completed searches, the best validation state passes through an ancestor that was not highest-scoring at its depth. These results show how local rule edits can support the exploration of useful revision paths and yield compact skills, with additional offline evaluations used to explore alternative states.
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cs.AIcs.CL Dongzhuo Li, Fangzhou Cheng, Weiwei Li et al. · Oct 14, 2026

Standard ReAct agents carry every failed attempt and off-path observation in one linear context, which eventually buries the evidence they need. TreeFlex solves this by saving intermediate states as nodes in a search tree and letting the same language model choose where to resume and what to do next, operating in two roles—Reflection for global navigation and Execution for local work—trained end-to-end with a tree-aware adaptation of GRPO. The paper shows that this design improves accuracy on deep research and software engineering benchmarks, especially on harder tasks, though it comes with higher inference costs and small-scale training.

A ReAct-style agent accumulates observations, intermediate results, and failed attempts in a single context. As this context grows, stale and off-path information consumes its limited capacity and obscures relevant evidence, making focused reasoning increasingly difficult. We introduce TreeFlex, a framework in which the agent's own policy decides where to search. The agent records each intermediate state, with a short summary, as a node in a search tree maintained by the harness. The policy is a single language model that acts in two roles. In the Reflection role, it has a global view of the tree through these summaries and picks a node to resume, together with an instruction. In the Execution role, the harness restores the path that led to that node, and the model carries out the instruction with the usual task tools until it saves a new node or proposes a solution, which Reflection then approves or sends back to another node. Through these choices, the policy decides whether to deepen the current line, branch from or revisit an earlier state, verify a proposal, or stop, without a fixed traversal order or a score for each node. We train navigation, task actions, checkpointing, and proposal review jointly with a tree-aware adaptation of GRPO, using task-level outcome rewards augmented by process rewards. After small-scale RL of a 4B model, with the same active-context limit for all methods, TreeFlex reaches 48.8% accuracy on a challenging deep-research benchmark, versus 41.5% for flat ReAct and 42.8% for FoldAgent, and its Pass@8 is about ten points higher than either. On SWE-bench Verified, with all three systems trained with RL from the same 9B model, TreeFlex resolves 54.9% of tasks, versus 43.3% for FoldAgent and 45.2% for its step-wise variant.
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cs.LGcs.AI Sifan Yang, Hongyi Tao, Dingzhi Yu et al. · Oct 14, 2026

Training large language models is memory-intensive, and subspace projection methods like GaLore can diverge when stochastic noise dominates the selected low-rank gradient space. This paper proposes SMRC and PMRC, which keep optimizer states in a low-dimensional subspace while adding the orthogonal residual gradient back into the parameter update. The authors prove $O(T^{-1/4})$ convergence rates for momentum SGD and for Muon under a mixed stationarity measure, and demonstrate empirical gains on LLM pretraining and fine-tuning up to $1.3$B parameters.

Memory-efficient subspace optimization has emerged as a practical approach to reducing the memory cost of LLM training while preserving optimization performance. Previous algorithms typically rely on the leading singular subspace of stochastic gradients, yet the gradient noise may dominate the subspace in later training stages and can prevent convergence. To overcome this limitation, we adopt a residual correction framework, which maintains the optimizer states in the subspace and adds the orthogonal residual gradient to the parameter update. We first integrate this scheme into momentum SGD to develop SMRC, which attains an $O(T^{-1/4})$ convergence rate for a fixed orthonormal basis, matching that of full-space momentum SGD. Our analysis introduces a subspace virtual iterate to resolve the coupling between the momentum and the residual correction. Furthermore, we extend SMRC to a multi-stage variant which periodically recomputes bases to track the evolving dominant subspace and retains the same rate. Since each basis refresh breaks the consistency of the virtual iterates, we devise a boundary correction approach that aligns them across stages. Beyond momentum SGD, we incorporate our framework into Muon and propose PMRC, which applies the matrix sign to the projected momentum. Through a weighted momentum tracking analysis that accounts for the residual gradient, we establish an $O(T^{-1/4})$ convergence rate for PMRC, which matches the rate of full-space Muon. We also design a multi-stage PMRC with periodically refreshed bases, which maintains a convergence rate of the same order. Extensive experimental results confirm the effectiveness and efficiency of our algorithms.
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cs.CLcs.AI Fiorenzo Parascandolo, Enver Sangineto, Xiaoyi Yu et al. · Oct 14, 2026

Length-Conditioned Majority Voting (LCMV) improves LLM reasoning by exploiting the empirical bias that longer chain-of-thought traces are less likely to be correct. Instead of filtering out long responses, it learns a logistic prior over correctness conditioned on CoT length and adapts it at test time using only unlabeled data and pseudo-labels from standard majority voting. The method is model-agnostic, adds negligible computational overhead, and is evaluated across 11 models and 8 benchmarks, making it a pragmatic drop-in replacement for standard MV.

Majority Voting (MV) is a simple and widely used strategy which improves the reasoning accuracy of Large Language Models (LLMs) by allocating additional inference-time computation. Specifically, in MV multiple Chain-of-Thoughts (CoTs) are independently sampled and the most frequent final answer is selected. In this work, we propose Length-Conditioned Majority Voting (LCMV), a Test-Time Training approach which improves MV leveraging an empirical observation that has recently been established in several studies: longer CoTs tend to be associated with a lower probability of correctness. We formulate this inductive bias as a length-conditioned prior probability, which is modeled by a simple logistic function. Moreover, we adapt this prior at test time using only unlabeled testing data and without fine-tuning the LLM. Finally, the adapted prior is used to weight the vote of each sampled answer. Extensive experiments across multiple LLMs and reasoning benchmarks show that LCMV consistently improves over both standard MV and existing length-based and confidence-based aggregation strategies, while retaining the simplicity and model-agnostic nature of MV. Our code is available at: https://github.com/aimagelab/LCMV.
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cs.AI Yuanfan Li, Junyi Chen, Qi Zhou et al. · Oct 14, 2026

The paper studies Protection Mode: a tendency of frontier language models to prioritize protecting a low-risk living subject over an object facing greater immediate physical damage. The authors introduce ProtectionBench, a controlled benchmark of 285 prompts spanning 34 physical scenarios, and find that models frequently choose the subject first even when correctly assessing the object as higher-risk. This matters for understanding how safety alignment and reasoning interact in high-stakes agent decisions.

Frontier language models excel at complex tasks yet may prioritize protection over larger physical consequences in simple, urgent decisions. GPT-5.6 Sol, for example, moves a girl playing in shallow water before retrieving a submerged camera. We call this Protection Mode and study it with ProtectionBench: 285 prompts, 34 physical families, and nine models. At lowest effort, at least one of four responses prioritizes the subject on 34.74% of Sol prompts and over 83% of MiniMax M3 and Qwen3.5-27B prompts; none of four independent human raters does so. Controls show that choices usually track physical risk. We elicit both risks before requesting an action. Some models assess risk incorrectly; others state the correct ordering but still choose the subject. Qwen3.5-27B with thinking shows 100% correct risk ordering but 57.81% subject choice among eligible conversations on eight selected scenes. Attention audits find no stable reduction in attention to relevant facts; removing the stated risk direction reduces object-first choice in dots3-note-prev but not detectably in Qwen3.5-27B. Adding a general "people or animals before property" rule increases subject choice by 19-38 percentage points, whereas factual reminders favor the object by 0.7-5.2 points. Removing naturally generated versions of that rule lowers subject choice by 10-15 points. We also examine whether post-training introduces this pattern. Base models already show Protection Mode; post-training changes justifications more than choices.
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cs.ROcs.AI Ziyan Liu, Jiting Liu, Weihong Zhong et al. · Oct 14, 2026

Existing robot policies use a single fixed parameter configuration across all interaction contexts, which forces shared weights to reconcile competing adaptation signals from diverse manipulation operations. MorphAct addresses this by introducing two coupled generators that synthesize context-dependent low-rank updates for the vision-language and action modules, where the action-side generator is conditioned on the adapted visual-language representations. This allows the effective policy weights to morph at each replanning step without test-time optimization or operation labels. Evaluations across three VLA backbones ($\pi_0$, $\pi_{0.5}$, and X-VLA), two simulation benchmarks, and four real-world tasks report closed-loop success gains of up to 16.30%, accompanied by ablations isolating the value of contextual generation and cross-module coupling.

Progress toward general intelligence in the physical world requires scaling robot learning across diverse environments and interactions. However, existing robot policies use shared parameters that remain fixed across interaction contexts. When different operations favor competing parameter adjustments, fitting their mixture can leave individual operations insufficiently adapted. Our atomic-task diagnostics reveal competing update directions in both vision-language and action parameters, with source-improving updates increasing loss on other tasks. This motivates MorphAct, a contextual parameterization framework that dynamically adjusts robot policy parameters as interaction contexts change. Two coupled generators produce context-dependent low-rank updates for the vision-language and action modules. Their coupling follows the policy's computational dependency: vision-language updates shape the representations that condition action-side parameter generation. Both generators are trained jointly through the native action objective, without operation labels or expert-adapter targets. MorphAct improves performance across three VLA backbones on LIBERO and Meta-World, with gains of up to 16.30%. In real-world evaluation, it achieves gains of up to 14% over $\pi_{0.5}$. Ablations support the benefits of contextual parameter generation and representation coupling.
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cs.AIcs.MA Yuran Wu, Mengkang Hu, Qionglin Qiu et al. · Oct 14, 2026

Long-horizon tasks like real-world software engineering expose the brittleness of monolithic agent loops, where a single model must simultaneously decompose, execute, and verify within one trajectory. LAGO addresses this by treating specialized language agents as temporally extended options—encapsulating role specifications, intra-option policies, termination conditions, and verifiers—that a meta-agent can retrieve from a persistent library or spawn on demand. The core proposition is that this hierarchical scaffold turns task decomposition into a reusable, growing component that requires no weight updates, and the authors report 58.6% on the full 500-task SWE-bench Verified with a frozen Qwen3.5-35B-A3B.

Long-horizon tasks expose a weakness of monolithic tool-use loops: one agent must decompose, execute, and verify a task within a single trajectory. We introduce LAGO, which treats specialized language agents as reusable temporally extended options. A meta-agent retrieves options from a persistent library or spawns new ones, dispatches sub-tasks, verifies results, and admits successful novel options. The library grows across tasks without updating model weights. On 500 SWE-bench Verified tasks, frozen Qwen3.5-35B-A3B in both roles resolves 58.6% under single-attempt evaluation with the official Docker evaluator. On a fixed 150-task subset, we re-run mini-SWE-agent, Terminus 2, and LAGO with the same policy, temperature, task IDs, and evaluator; their resolve rates are 49.3%, 57.3%, and 60.3%, respectively. Cross-model experiments provide evidence consistent with a role for decomposition quality. A 50-task component ablation finds four fewer resolved tasks without decomposition, two fewer with shuffled reused content, and six fewer without the library. These results support reusable agent-options as a practical abstraction for task streams, while leaving component-level causality task- and model-dependent.
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cs.LGcs.AIstat.ML Amartya Banerjee, Harlin Lee, Caroline Moosm\"uller · Oct 14, 2026

Population dynamics are often observed only as unpaired snapshots, leaving the evolution between measurements fundamentally underdetermined. This paper introduces Neural Wasserstein Splines (NWSP), a method that learns a continuous curve of distributions by penalizing the intrinsic Wasserstein acceleration rather than the acceleration of individual particles, which is representation-dependent. It couples a neural spline generator with a finite-dictionary projection of velocity and its time derivative, achieving competitive results on synthetic and single-cell benchmarks.

Population dynamics are often observed only as unpaired snapshots, which leave the evolution between measurements underdetermined. Second-order regularization can constrain it, but a penalty on the accelerations of sampled particles is a prior on joint particle paths, and different particle representations of the same marginal curve can have different acceleration costs. We therefore introduce Neural Wasserstein Splines (NWSP), a sample-based method that learns a continuous population curve under a Wasserstein smoothness prior. A neural network maps latent variables to the control points of a cubic spline in time, so samples at any time come from the spline basis without numerical integration. We project the generator's velocity onto gradients of a finite dictionary of scalar potentials and differentiate this measure-dependent projection in time, obtaining a finite-dimensional surrogate for the intrinsic Wasserstein acceleration, trained jointly with distributional fit losses. For a fixed dictionary and ridge parameter, we prove that the population penalty depends only on the marginal curve and bound its sensitivity to moment-estimation errors. Learned potentials (NWSP-N) sharpen acceleration estimates. On various synthetic and single-cell benchmarks, NWSP is highly competitive with transport and flow-based methods, ranking in the top two in 11 of 16 settings. The penalty improves on an unregularized spline in 13 of 16 settings and, while competitive with a particle-acceleration penalty, adds provable representation invariance.
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cs.AI Simon Baur, Sumire Honda, Wojciech Samek et al. · Oct 14, 2026

Reliable uncertainty quantification for reasoning LLMs is expensive when it requires sampling multiple long chain-of-thought traces, and token-level signals collapse or mis-calibrate on deep reasoning. This paper introduces Argument Graph Uncertainty (AGU), a post-hoc framework for multiple-choice QA that segments a single reasoning trace into propositional nodes, scores pairwise and node-to-option relations with a small NLI model, and aggregates the resulting evidence into a Dirichlet posterior over answer options. The concentration of that posterior, expressed as normalized entropy $U_{\mathrm{AGU}}(R) = H_{\mathrm{norm}}$, yields an uncertainty estimate that is cheap to compute and structurally grounded.

Reliable uncertainty estimation is essential for deploying large language models in high-stakes reasoning tasks, yet most existing approaches rely on expensive sampling strategies or shallow token-level signals that ignore the internal logical structure of model outputs. We introduce Argument Graph Uncertainty, a post-hoc framework for multiple choice question tasks, that estimates model confidence directly from the logical structure of a single chain-of-thought reasoning trace. Our method uses either a lightweight instruction-tuned model or a simple deterministic rule to segment the reasoning chain into propositional units, then applies a NLI model to infer relational edges and construct two complementary argument graphs over these segments. The resulting edge scores are aggregated into a Dirichlet posterior over answer options, whose concentration yields calibrated uncertainty estimates reflecting both local step-to-step coherence and global logical consistency across the reasoning trace. Evaluated on GPQA, MMLU-Pro and TruthfulQA, our method consistently surpasses token-based and consistency-based uncertainty baselines across multiple reasoning models. We further demonstrate through extensive combination analyses that argument graph uncertainty captures an orthogonal signal to existing approaches, making it a complementary component in uncertainty ensembles. Crucially, our framework requires no additional calls to the evaluated model and relies entirely on small, efficient auxiliary models, producing fully interpretable, per-node uncertainty attributions at low computational cost.
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cs.LGcs.AI Wei Chen, Yubing Wu, Zhou Xu et al. · Oct 14, 2026

Hindsight-Privileged RLVR tackles the inefficiency of group-based RLVR methods like GRPO, which require multiple rollouts per prompt and lose their learning signal when all sampled outcomes are identical. The core idea is to replace group comparisons with a single rollout per prompt, using the trajectory's own realized future as training-only privilege: a frozen snapshot of the generating policy scores each token under both causal and hindsight views, and normalized Jensen--Shannon divergence between these full-vocabulary distributions weights a historically centered reward. This yields bounded token-level credit without a learned critic or reference solution, training $1.2$--$2.3\times$ faster than GRPO on Qwen3-8B but with task-dependent accuracy tradeoffs.

Reinforcement learning with verifiable rewards (RLVR) trains language models from checked task outcomes, but assigning a terminal reward to individual reasoning tokens or actions remains difficult. Group-relative methods such as Group Relative Policy Optimization (GRPO) sample several attempts per prompt, but lose their reward-based learning signal when all attempts receive the same outcome. We propose Hindsight-Privileged RLVR (HP-RLVR), a single-rollout method that turns a completed trajectory's own future into token-level update weights. The generating policy snapshot scores each eligible token under its causal history and under a hindsight context containing the realized future and verifier feedback. A normalized Jensen--Shannon divergence between the two views weights the reward relative to a historical baseline, yielding bounded token credit for both successful and failed attempts, with no reference solution or learned critic. In paired Qwen3-8B runs over a shared $100$-step schedule, HP-RLVR trains $1.21\times$, $1.46\times$, and $2.30\times$ faster than GRPO on mathematics, code generation, and ALFWorld, using one eighth the rollouts per prompt. Accuracy is comparable overall, with HP-RLVR ahead on mathematics at all three sizes and GRPO ahead on code and ALFWorld. In ALFWorld, $43.2\%$ (4B) and $49.0\%$ (8B) of GRPO's gradient-norm records are zero, versus none for HP-RLVR.
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cs.CVcs.AI Siqi Yang, Yimu Wang, Ziqi Cai et al. · Oct 14, 2026

PAWA tackles multi-agent world modeling in shared environments like Minecraft, where one player's actions change what every other player sees—not just in their local field of view, but in directions they are not currently looking. The core idea is to jointly forecast each player's point-of-view (POV) video alongside a world-stabilized panoramic video, conditioned on all players' actions. The model uses a dual-tower architecture with ray-aligned cross-attention that links tokens viewing the same world direction regardless of whether they appear in rectilinear POV or equirectangular panorama coordinates, plus a quadratic-phase player encoding that scales identities as $m^2$ instead of $m+1$. The work also introduces a scalable dataset pipeline that records gameplay without graphics clients and renders replays offline, supporting more than 64 simultaneous players.

A multiplayer world model must predict how the independent actions of several players change a shared environment, including changes outside a player's current field of view. A point-of-view (POV) video captures such changes only after they enter its field of view, whereas panoramic video records the surroundings in every viewing direction and has served as an intermediate representation of the world state in recent world models. Learning this task therefore requires synchronized POV and panoramic videos of interacting players together with their actions, yet no existing dataset provides this combination in Minecraft, an established testbed in which players act independently in a shared, modifiable 3D world. We present PAWA, a dataset and framework for action-conditioned panoramic multiplayer world modeling. The dataset pairs each player's POV video with world-stabilized panoramic video and aligned actions. Its distributed pipeline decouples CPU gameplay capture from GPU rendering, scales beyond 64 simultaneous players, and re-renders each recorded session under new observation configurations without replaying the gameplay. On this dataset, we develop a dual-tower model that jointly predicts POV and panoramic video and couples the two streams through cross-attention that aligns tokens observing the same direction in a shared world frame. We further introduce a quadratic-phase player encoding that provides many more player codes than existing rotary codes at the same embedding dimension. Experiments show that PAWA outperforms state-of-the-art multiplayer world models in POV prediction quality while also producing high-fidelity panoramic predictions. The dataset and collection pipeline are open source to support further research on multiplayer world models.
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cs.LGcs.AImath.OC Kaifei Wang, Zikang Shan, Liwei Wang et al. · Oct 14, 2026

Momentum is a pillar of modern optimization, yet its benefits in reinforcement learning with verifiable rewards (RLVR) remain unclear. This paper studies a KL-regularized bandit formulation of RLVR and proves that, with exact policy gradients, larger EMA coefficients strictly accelerate convergence within a safe overshoot-free range. Its central insight is that stochastic sampling obscures this gain unless the coefficient scales with the learning rate so that $\eta/(1-\beta)$ stays constant, a principle validated in bandits and in LLM post-training on Qwen models.

Momentum is a classical tool for accelerating convex optimization and a standard component of modern large language model training. Yet recent empirical work has questioned the usefulness of first-moment momentum in reinforcement learning with verifiable rewards (RLVR). We study this question through a bandit formulation of RLVR with bias-corrected exponential moving average (EMA) momentum, where the EMA coefficient $\beta$ controls how quickly the weights on past gradients decay. When policy gradients are evaluated exactly, we prove that increasing $\beta$ within a range that prevents overshoot strictly accelerates optimization. When gradients are estimated from sampled responses, a positive expected gain can be obscured by sampling fluctuations. We show that as the learning rate $\eta$ decreases, the expected gain with fixed $\beta$ vanishes faster than these fluctuations, whereas increasing $\beta$ to keep $\eta/(1-\beta)$ within the safe regime preserves a nonvanishing gain that eventually dominates them. Bandit simulations quantitatively validate these predictions. RLVR experiments on Qwen3-4B-Base using SGD with EMA and AdamW support our principle of choosing larger coefficients in practical LLM post-training. On Qwen2.5-32B with AdamW, simply increasing $\beta_1$ improves mean validation accuracy by nearly $2$ percentage points over the conventional choice, demonstrating the principle's effectiveness at a larger model scale.
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cs.AI Foteini Oikonomou, Maria Pantazi-Kypraiou, George Goudroumanis et al. · Oct 14, 2026

Post-legalization placement refinement seeks to reduce wirelength after global placement without breaking site constraints. This paper audits whether a GNN-PPO agent can handle that task by systematically exploring 18 training configurations on three ISPD2015 benchmarks, varying rewards, action spaces, GNN architectures, and graph-partitioning strategies. The study finds that RL lags behind classical tools, and it dissects why—pinning blame on credit-assignment bottlenecks, GNN over-smoothing, and netlist regularity—while proposing a lightweight netlist classifier to guide training decisions.

Graph Neural Networks (GNNs) and Reinforcement Learning (RL) have recently been explored for VLSI placement optimization, but their effectiveness for post-legalization placement refinement remains unclear. This paper presents a systematic design space exploration of a GNN-Proximal Policy Optimization (GNN-PPO) framework across three ISPD2015 benchmarks. We evaluate 18 configurations covering reward functions, GNN architectures, action spaces, candidate-set sizes, and training strategies. We analyse the results we obtain to identify pitfalls and to assess the prospects and opportunities of the RL methods for post-legalization placement. On top of that we propose a design classification approach to guide the design decisions of RL models.
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cs.CVcs.AI Imen Bajar, H\'eber Hwang Arcolezi, Antoine Boutet et al. · Oct 14, 2026

This paper asks whether releasing learned embeddings from pretrained brain MRI encoders—instead of raw scans—actually protects patient privacy. The authors audit five diverse encoders on two longitudinal datasets, measuring patient linkage, re-identification, and sex-attribute inference under an explicit attacker model. They find that several embeddings retain enough subject-specific structure to enable rank-1 re-identification above 90% on both datasets, and that sex can be inferred with balanced accuracy up to 95.5%. The core takeaway is that embedding release alone is insufficient to establish anonymity.

Pretrained representations are increasingly used to share and reuse information from medical images without exposing the original scans, but it is unclear how much patient-specific information these representations retain. We investigate this question for brain magnetic resonance imaging (MRI) by evaluating five frozen pretrained encoders spanning different architectures, pretraining objectives, and training domains on two longitudinal T1-weighted datasets, OASIS-2 and MIRIAD. Under an attacker model with access to released embeddings, the corresponding public encoder, and auxiliary MRI scans, we evaluate patient linkage and sensitive-attribute inference. Across the evaluated representations, we observe substantial subject-specific information: rank-1 patient linkage reaches up to 99\% on MIRIAD and exceeds 90\% on OASIS-2 for the highest-risk representation, despite the absence of an identification objective during encoder training. We further show that the released embeddings retain information about a demographic attribute, with recorded-sex prediction reaching balanced accuracy of 90.9\% on OASIS-2 and 95.5\% on MIRIAD. Overall, our results demonstrate that replacing raw brain MRI with learned embeddings does not, by itself, eliminate patient-linkage or attribute-inference risk, and is therefore insufficient on its own to establish anonymity.
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cs.CRcs.AI Behrad Tajalli, Henk Berendsen, Xiaoyun Xu et al. · Oct 14, 2026

This paper reframes backdoor stealthiness in deep neural networks as a multi-space measurement problem rather than a single latent property. The authors benchmark ten attacks across four datasets and three architectures, measuring observable footprints in input, feature, and parameter space to show that stealthiness is fragmented: an attack can be quiet in one space and conspicuous in another. They also introduce two diagnostic metrics—CDBI and TUP—to address blind spots in global feature clustering and channel-level concentration. The central message is that future stealthiness claims should be backed by evidence from all three spaces, not by a single metric or defense.

Backdoor attacks on deep neural networks are commonly evaluated by attack success rate and benign accuracy, yet their stealthiness remains inconsistently defined and measured. Existing work often studies only one observable aspect of stealthiness, such as trigger imperceptibility, feature-space separability, parameter-space concentration, or evasion of particular defenses. This creates a fragmented picture: an attack may appear stealthy under one metric while leaving conspicuous footprints elsewhere. This paper presents a tri-space measurement study of backdoor stealthiness in image classification. We distinguish latent stealthiness---the ideal but unobservable difficulty of distinguishing a backdoored system from a benign one---from measurable footprints in three spaces: input, feature, and parameter space. Under this framework, we evaluate representative backdoor attacks across four datasets and three model architectures using a broad suite of footprint metrics. Our results show that stealthiness is not monolithic: attacks that are quiet in one space are often loud in another, and existing attacks rarely achieve consistently small footprints across all three spaces. We further analyze agreement and disagreement among stealthiness metrics and study how footprint measurements interact with attack success rate. Based on observed blind spots in existing measurements, we introduce two diagnostic metrics: Class-Specific Davies--Bouldin Index (CDBI), which captures class-conditional feature overlap, and TAC--UCLC Product (TUP), which identifies channels that are both trigger-responsive and downstream influential. These metrics are intended to augment, not replace, the broader measurement suite. Finally, we provide practical guidance for future stealthiness evaluations.
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cs.LGcs.AI Haruki Settai, Tadashi Kozuno, Shinji Ito · Oct 14, 2026

Semi-gradient TD with nonlinear function approximation is notoriously unstable because the bootstrap target moves as the parameters evolve. This paper studies the problem in the mean-field regime for two-layer neural networks and identifies a stability regime where entropy-driven relaxation dominates the sensitivity of the moving target. Under the resulting condition, the authors prove exponential last-iterate convergence and quantify the regularization bias, then extend the same mechanism to soft Q-learning.

Semi-gradient temporal-difference learning is a core algorithmic component of reinforcement learning, but bootstrapping with function approximation generally induces a non-conservative vector field and can lead to instability. We analyze this effect for two-layer neural networks in the mean-field regime and identify a simple stability mechanism in which entropy-induced relaxation dominates the sensitivity of the moving bootstrap target. Under this condition, we prove exponential convergence to a unique fixed point and quantify its bias relative to the unregularized Bellman solution. We also show that the same mechanism extends to entropy-regularized off-policy control through soft Q-learning.
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cs.LGcs.AI Tinglan Wang, Haixu Liu, Shaobo Chen et al. · Oct 14, 2026

MeanFlow normally couples the prediction horizon $h_k$ to the update step $\delta_k$. This paper decouples them, showing on CIFAR-10 that longer horizons hurt FID near the source $(t=0)$ but help at the midpoint $(t=0.5)$, and that this midpoint gain depends on earlier guidance choices. A frozen four-query rule improves mean FID by 2.0 without retraining or extra calls, yet ImageNet calibration finds no benefit beyond shifting query starts. The work establishes prediction horizon as a distinct but configuration-sensitive inference control.

MeanFlow predicts interval-average velocities, but conventional few-step sampling ties the interval queried from the model to the duration of the state update. We separate these two quantities at inference, fixing the model, update grid, and number of queries while varying the prediction horizon. Our central finding is that the horizon response depends on both query position and the states entering that query. Across seven independently trained CIFAR-10 checkpoints at classifier-free guidance (CFG) scale 2, a longer horizon worsens FID at early steps but improves it at the midpoint. To probe whether query time alone determines this response, we fix the midpoint query and current/subsequent guidance while changing only earlier CFG. In held-out factorial outcomes on five previously studied checkpoints, the mean midpoint horizon benefit increases from 0.109 to 1.308 FID, indicating sensitivity to the incoming-state distribution. A frozen four-query rule reduces mean CIFAR-10 FID by 2.023 without retraining or extra queries, including gains on five checkpoints trained after rule selection. A milder rule also improves mean FID by 1.041 on a stronger frozen grid, with fixed-rule FID gains on the evaluated public ImageNet-256 and AFHQ checkpoints. However, matched-budget calibration favors query-start shifting in historical CIFAR tests, and the tested Horizon allocation adds no FID benefit beyond Grid+Start on two public ImageNet models. Thus, prediction horizon is a distinct, position- and state-sensitive inference control, but not a universally preferred one.
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cs.SDcs.AIcs.CL Puneet Mathur, Dinesh Manocha · Oct 14, 2026

Multi-party floor control is the next bottleneck for full-duplex voice agents: systems must decide not just when speech ends, but whether overlapping listeners are backchanneling or genuinely taking the floor. MultiPartyTurnBench introduces 240 synthetically generated, channel-separated conversations spanning two to five speakers and six interaction types, evaluating End-of-Turn (EOT) and Interruption (INT) detection with exact causal annotations. The results reveal a stark capability asymmetry: turn completion is largely tractable, while selective interruption handling remains near chance even for state-of-the-art commercial agents.

Full-duplex speech systems must decide when to enter, hold, or relinquish the conversational floor, even as multiple speakers overlap or backchannel without taking it. Existing evaluations study dyadic turn-taking or end-to-end agent behavior, but lack a unified, controlled evaluation of genuine floor transitions against confusable non-events in multi-party settings. We introduce MultiPartyTurnBench (MPTB), a benchmark of 240 synthetically generated, channel-separated conversations spanning two to five speakers and six interaction types. MPTB evaluates two complementary tasks: End-of-Turn (EOT) detection distinguishes genuine turn completion from temporary holds, while Interruption (INT) detection distinguishes successful floor takeovers from non-floor-taking speech. Exact event-conditioned annotations enable causal evaluation using false-positive-constrained recall and signed latency. Across acoustic, semantic, and turn-projection baselines, we find a stark asymmetry: learned systems achieve 82.5-92.6% EOT recall at 4.3-11.8% false-positive rates, while INT detection suffers from missed takeovers or excessive false activations. This asymmetry extends to five full-duplex agents which achieve 86.1-95.8% balanced accuracy on turn entry, yet perform near chance (46.9-54.7%) on selective interruption handling. Gemini-3.8-Live yields to 97.7% of backchannels, whereas MiniCPM-o-4.5 yields to only 1.4% of genuine interruptions. These findings establish selective floor control as a distinct, unresolved challenge for reliable multi-party voice interaction.