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cs.LG Yaroslav Gusev, Eugene Golikov, Dmitry Yarotsky · Oct 14, 2026

The paper studies how classification accuracy evolves when neural networks are trained from very small initialization. It identifies the "accuracy well": a striking non-monotone trajectory where accuracy first rises rapidly, then drops significantly, and only recovers much later. The authors argue this reveals learning stages invisible to the training loss, and they support the claim with experiments across architectures and datasets, plus rigorous theory for deep linear networks.

We study classification dynamics under small initialization and identify a pronounced non-monotone behavior of accuracy that we call the accuracy well: accuracy rises rapidly early in training, subsequently drops, and only much later recovers. We observe this phenomenon in deep linear networks, fully connected ReLU networks on MNIST, deep convolutional networks on CIFAR-10, and controlled synthetic tasks, across different losses and optimizers and in both training and test accuracy. We propose a three-stage explanation in terms of target-driven organization, a degeneracy bottleneck, and subsequent recruitment and recovery. We develop a rigorous theory of these dynamics for shallow and deep linear networks, showing in particular that high accuracy can emerge while the predictor and the change in loss remain asymptotically vanishing, before continued optimization causes accuracy to deteriorate. For a simple synthetic classification task, we prove an extreme instance in which accuracy asymptotically rises to 100%, collapses to 0, and later recovers permanently to 100%. Our results show that classification accuracy can reveal aspects of learning dynamics that are not captured by the training loss alone.
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cs.CVcs.LG Bilal Sidiqi, Yipei Wang, Wen Yan et al. · Oct 14, 2026

Prostate MRI segmentation suffers from regional boundary ambiguity, causing standard global-overlap losses to overlook clinically significant surface deviations. This paper proposes Contrastive Uncertainty Learning (CUL), which treats predictive uncertainty as a representation-level supervisory signal rather than a post-hoc filter: low-uncertainty same-class voxels are clustered in embedding space while high-uncertainty or misclassified voxels are actively repelled. Evaluated on 589 lower-pelvic MR scans across eight anatomical structures, CUL preserves mean Dice while significantly improving surface-sensitive metrics and suppressing extreme errors in hard cases, suggesting practical value for radiotherapy planning and contour-acceptance workflows.

Boundary delineation of anatomical structures in prostate MRI is often compromised by regional ambiguity. Automated segmentation methods relying on global overlap loss functions tend to be insensitive to surface deviations, leading to significant errors in ambiguous regions. Most existing uncertainty-aware methods treat uncertainty as a post-hoc quality indicator or prediction filter. We propose Contrastive Uncertainty Learning (CUL), a supervised framework that uses predictive uncertainty to directly guide representation learning. Using Monte Carlo Dropout, CUL identifies voxel-wise uncertainty and structures the embedding geometry accordingly: low-uncertainty, correctly predicted features form stable voxels while high-uncertainty or misclassified features are actively repelled, preventing feature collapse at difficult boundaries. We evaluate CUL on a 589-scan 3D prostate MRI multi-structure segmentation task (8 anatomical structures) using a ViT with UperNet decoder architecture. Average Dice ($83.38\%$) remains comparable to the baseline ($83.35\%$), while surface distance decreases significantly ($p<0.001$) across 6 of 8 anatomical structures. A hard-case analysis reveals a $22{\times}$ asymmetry between significantly improved and degraded cases ($18.8\%$ vs $0.9\%$). Ablation studies show that removing uncertainty-guided sample selection eliminates improvements for the transition zone, while replacing the contrastive objective with a boundary loss additionally removes bladder improvements, demonstrating that both uncertainty-guided sampling and the contrastive objective are essential for the observed gains. These findings demonstrate that the proposed uncertainty-guided representation learning is a useful mechanism for reducing the risk of extreme errors in safety-critical medical segmentation
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cs.LG Yuanhao Zhuo, Zixi Qin, Ling Qin et al. · Oct 14, 2026

Clinical assessments collected across heterogeneous systems create mixed longitudinal records that resist standard total-score linking. This paper proposes Bidirectional Feature Harmonization Decomposition (BFHD), a method that identifies which individual measurements can be reliably translated between two assessment systems in both directions while explicitly separating out non-translatable components. By operating directly in original measurement spaces via a shared invertible backbone and feature-wise output gating, BFHD aims to provide an interpretable decomposition for cross-protocol integration and longitudinal analysis.

Clinical assessments are often collected using heterogeneous assessment systems across centers and time, leading to records that mix different but related sets of measurements. This motivates harmonization beyond total-score linking. We formulate clinical harmonization at the measurement level as a bidirectional recoverability problem: given paired observations from two assessment systems, the goal is to identify which measurements can be reliably translated in both directions within an application-defined tolerance, while separating non-translatable components. We propose Bidirectional Feature Harmonization Decomposition (BFHD), a feasibility-driven framework that enforces bidirectionally coupled translation and uses feature-wise output gating to produce an explicit decomposition in the original measurement space. Experiments on synthetic data and real clinical assessment pairs show that BFHD achieves broader feasible harmonization coverage and improved subset stability compared to baselines.
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cs.IRcs.LG Yuanfeng Qiu · Oct 14, 2026

Graph collaborative filtering models collapse in strict cold-start settings because zero-degree items sever the message-passing chain. DualGCN tackles this with an asymmetric two-branch distillation framework: a teacher network anchors item representations with frozen semantic priors smoothed over the graph topology, and a lightweight student learns to project unseen semantic features into that collaborative space via cosine distillation and residual mapping. If the claims hold up, it offers a much leaner alternative to heavy multi-modal fusion modules for industrial retrieval.

Graph Collaborative Filtering models have achieved remarkable success in recommendation systems. However, they inherently suffer from a catastrophic representation collapse in strict cold-start scenarios due to the topological isolation of unobserved items. While integrating multi-modal semantic features offers a potential remedy, directly mapping isolated semantic attributes into a globally topology-driven collaborative space frequently precipitates representation degradation and optimization conflicts. To bridge this fundamental structural divide, we propose DualGCN, an innovative Dual-Branch Graph Knowledge Distillation Framework. Operating under a decoupled two-stage training paradigm, DualGCN first constructs a robust collaborative teacher network where item representations are anchored by a topology-smoothed semantic prior, effectively reshaping the latent manifold. Subsequently, a semantic student branch employs a residual mapping mechanism and a magnitude-agnostic cosine distillation objective to achieve high-fidelity cross-modal alignment without disrupting established collaborative signals. Furthermore, we introduce a dynamic norm reconstruction mechanism to rigorously calibrate the physical scales of novel and warm items during global retrieval. Extensive experiments across three real-world benchmark datasets demonstrate that DualGCN significantly outperforms state-of-the-art baselines in strict cold-start scenarios while comprehensively preserving recommendation accuracy for highly active items.
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cs.LGcs.CV Yuwei Sun, Siyu Zhu · Oct 14, 2026

Latent world models based on Joint-Embedding Predictive Architectures (JEPA) offer a scalable route to embodied planning, but existing methods suffer from representational collapse, heavy compute, and weak long-horizon reasoning. This paper proposes MemWM, a lightweight JEPA world model augmented with a content-addressable associative memory bank that supplies high-level subgoals via Adaptive Layer Normalization. By operating at multiple temporal scales within a shared latent space and enforcing slot diversity through complementary losses, the authors aim to boost long-horizon performance without relying on pretrained encoders or doubling model size. Across four control tasks, MemWM achieves an average success rate of 89.9% with only 19M parameters, outperforming heavier baselines such as DINO-WM in aggregate.

World models trained via latent dynamics offer a scalable path for embodied planning, yet existing methods suffer from representational collapse, computational overhead, and limited long-horizon capability. We introduce a memory-enhanced latent world model that augments JEPA-style prediction with a content-addressable memory bank. Our approach learns high-level representations directly from observations, operating at multiple temporal scales within a shared latent space, and conditions predictions via adaptive layer normalization. To prevent collapse and ensure effective memory usage, we design two complementary losses that encourage slot diversity and balanced temporal utilization. Experiments on PushT, Tworoom, Reacher, and OGBCube demonstrate that our method achieves state-of-the-art performance with a lightweight architecture, outperforming conventional latent world models on long-horizon planning tasks.
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cs.LGmath.OC Yanyi Li, Wendao Wu, Haihan Zhang et al. · Oct 14, 2026

This paper resolves the open problem of optimal dimension dependence for dynamic regret in exp-concave online learning. The authors propose SparseGauss, a proper full-information learner that achieves a $\widetilde{O}(d^{1/3}T^{1/3}P_T^{2/3})$ rate via sparse Gaussian histories and square-root KL movement control. A matching lower bound on a Euclidean ball establishes minimax optimality, up to logarithms, when $T \gtrsim d^2$.

Tracking changing comparators is a central problem in online learning. For exp-concave losses, previous work established the $T^{1/3}P_T^{2/3}$ dependence on the horizon $T$ and Euclidean path length $P_T$ for fixed dimension, while the optimal cost of dimension remained unresolved. We resolve this question by establishing a sharp $d^{1/3}$ curved dimension factor, improving the $d^{2/3}$ factor of recent switching and interval reductions [1, 2]. To achieve this improvement, we develop a proper, full-information learner on compact convex subsets of $\mathbb{R}^d$ that adapts to the unknown path length and, under fixed dimension-independent diameter, gradient, and curvature parameters, guarantees $$\operatorname{Reg}_T(u_{1:T}) \le \widetilde{O}\left(d+\min\left\{d^{1/3}T^{1/3}P_T^{2/3},\sqrt{TP_T},T\right\}\right).$$ A matching lower bound on a diameter-one Euclidean ball establishes the minimax frontier up to logarithmic factors when $T\gtrsim d^2$, including the transition from the curved rate to larger path budgets. The lower bound already holds for losses that depend on only one coordinate per round, isolating an unavoidable cost of learning across directions. Our upper bound follows from square-root Gaussian KL control of comparator movement and a cancellation argument that pays for history restarts. The curved learner maintains $O(\log^2 T)$ Gaussian states, uses one gradient per round, and runs in time near-linear in $T$ under a Mahalanobis-projection oracle.
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cs.LGmath.PRstat.ML Ianis Hammani (ENS Paris Saclay, LMO), Claire Boyer (LMO et al. · Oct 14, 2026

Score-based generative models with heavy-tailed $\alpha$-stable Lévy noise have shown empirical promise for extreme-event modeling, yet theoretical guarantees remain scarce. This paper develops a non-asymptotic $W_p$ convergence framework for scale-preserving $\alpha$-stable dynamics and proves that global Wasserstein convergence alone does not separate stable from Brownian models on heavy-tailed targets. A sharp distinction emerges instead in the tails: stable dynamics inherit power-law tails with index $\alpha$, while Brownian outputs stay light-tailed, and asymptotically correct extreme-quantile scaling requires matching the target tail index $\nu$ to the noise index $\alpha$. These results establish tail-index matching as a principled design mechanism for capturing heavy-tailed phenomena.

Score-based generative models driven by $\alpha$-stable L{\'e}vy processes have been proposed as an alternative to Brownian diffusion models, with empirical evidence suggesting improved sampling and better modeling of heavy-tailed data. Yet theoretical guarantees for these models remain limited. We develop a non-asymptotic convergence analysis for scale-preserving $\alpha$-stable generative dynamics, covering both compactly supported and power-law targets. In p-Wasserstein distance, we quantify the effects of early stopping, initialization, score approximation, and time discretization, and show exponential decay of the initialization error. A comparison with Brownian dynamics reveals that global Wasserstein convergence alone does not fundamentally distinguish the two models: both initialization errors decay exponentially with the forward horizon on the common class of heavy-tailed targets. A sharp separation emerges instead in the tails. At any positive generation time, stable dynamics produces power-law tails with index $\alpha$, whereas Brownian dynamics remains light-tailed. For a target with tail index $\nu$, asymptotically correct extreme-quantile scaling is possible precisely when $\alpha$=$\nu$. These results identify tail-index matching as a principled mechanism behind the ability of stable generative models to capture extreme events.
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cs.LG Zinan Ling, Yang Xiao, Ruimeng Ye et al. · Oct 14, 2026

LLM unlearning is usually tested by whether a model refuses harmful queries and retains clean-task accuracy. The authors highlight a gap: models can pass those checks while failing when benign prompts sit just outside the forgotten domain, a failure they term forget-adjacent utility loss. They propose RA2, which redirects forget-token hidden states toward nearby retain-supported anchors instead of simply pushing them away. Experiments on WMDP and MUSE show this directional choice meaningfully reduces neighborhood-level collateral damage.

Large Language Model (LLM) unlearning is often evaluated primarily by target suppression and clean retain utility. These metrics can miss a local failure mode: a model may perform well on standard retain prompts, yet degrade on benign reasoning when prompts lie near the forgotten domain. This phenomenon is termed forget-adjacent utility loss. A fundamental question is: where should forget representations go after they leave the removed behavior? Successful unlearning depends not only on whether forget-conditioned representations depart from the harmful computation, but also on the direction in which they are redirected afterward. We propose RA$^2$ (Retain-Anchored Attraction), a latent-space unlearning method that redirects forget-token states toward nearby retain-supported representations while preserving higher-layer behavior on retain data. On WMDP and MUSE, RA$^2$ yields higher forget-adjacent utility than strong unlearning baselines at similar broad-utility levels. These results show that the migration direction of forget representations materially affects benign behavior near the forget boundary. Our code is available at https://github.com/ZacLing/retain_anchored_attraction.
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cs.ROcs.AIcs.LG Huixuan Cheng, Bike Zhang, Shankar Sastry et al. · Oct 14, 2026

This paper investigates whether high-performing humanoid control networks can be synthesized directly in weight space rather than trained conventionally. The authors adopt a latent diffusion framework---pairing a cluster-wise linear autoencoder with a Diffusion Transformer---to generate weights for 3-layer MLP policies on a Unitree G1 robot, achieving zero-shot sim-to-real transfer for walking, dancing, and spin kick. Alongside generation, they analyze the learned weights and identify a kinematic prior in first-layer parameters that emerges under both reinforcement and imitation learning, suggesting embodiment-specific structure in policy weights.

Recent advances in robot learning have driven rapid progress in humanoid control, enabling increasingly agile behaviors in the real world. However, humanoid control networks are typically obtained through conventional training procedures, while comparatively little attention has been given to directly modeling the distribution of their learned weights and generating functional networks in weight space. In this work, we investigate whether high-performing humanoid control networks can be generatively modeled directly through their weights. We adopt a latent diffusion framework that couples a linear autoencoder with a Diffusion Transformer. The autoencoder compresses actor network parameters into a compact latent space, and the Diffusion Transformer models the distribution of these latents. Trained on networks collected from reinforcement learning for the Unitree G1 robot, our approach generates deployable networks that perform various motions in the real world, including walking, dancing, and spin kick. Beyond generation, we further study the learned weight space to better understand the structure captured by these humanoid control networks. We identify a structural principle in the first-layer weights that consistently reflects the robot's kinematic prior. Notably, this kinematic prior emerges under both Reinforcement Learning (RL) and Imitation Learning (IL) training, suggesting that it is not specific to a particular optimization process but may instead reflect common knowledge associated with humanoid embodiment. Together, these results demonstrate the feasibility of generative modeling in humanoid network weight space, while providing initial insights into the information encoded by their learned weights. Additional results are available on our project website: https://humanoid-weight-diffusion.github.io/
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cs.ITcs.LGmath.IT Zhijie Su, Shiquan Zhang, Qiaolin He · Oct 14, 2026

This paper tackles digital-domain self-interference cancellation in in-band full-duplex radios, where conventional adaptive filters degrade when the desired signal is much stronger than the residual interference.
The authors reformulate cancellation as an operator-learning problem: a Transformer neural operator learns the temporal evolution of the self-interference channel from historical observations and reconstructs the current interference from the known transmit signal.
Trained in a desired-signal-free setting and applied during contaminated reception, the method reduces reliance on corrupted instantaneous updates and reports strong high-SIR stability.

Digital-domain self-interference cancellation is essential in in-band full-duplex radios after passive suppression and analog cancellation. It is particularly challenging when the desired signal is strong relative to the residual self-interference. In this regime, conventional iterative digital cancellers update their coefficients from desired-signal-contaminated received samples and may suffer substantial performance degradation. This paper reformulates digital-domain self-interference cancellation as an operator-learning problem. The proposed framework learns the temporal evolution of the residual self-interference channel from historical observations and uses the learned operator together with the known local transmit signal to reconstruct the current residual self-interference. A Transformer neural operator is used to realize this framework. The resulting method is trained in a desired-signal-free setting and then applied in the presence of a desired signal. A continuity-based analysis characterizes the sensitivity of the learned operator to the resulting input perturbation. Numerical experiments in static and time-varying channels, including time-varying SIR conditions, demonstrate stable cancellation performance over a wide range of interference levels. At 30 dB SIR, the proposed method improves the cancellation performance by 5--15 dB over the considered conventional methods.
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cs.LG Giorgio Morales, Anik\'o Ek\'art · Oct 14, 2026

Neural symbolic regression models are bottlenecked by training datasets riddled with structural redundancy and simplicity bias. This paper proposes ExCaUS, a deterministic grammar-based framework that exhaustively enumerates canonical univariate skeletons under explicit unary-count and depth bounds, eliminating duplicate functional forms. The authors pair this with a derivative-driven sampling strategy and a 150-problem benchmark, demonstrating that curated structural diversity exposes severe weaknesses in state-of-the-art SR methods.

Neural symbolic regression (SR) models require diverse datasets of mathematical expressions for robust training. However, existing datasets rely predominantly on stochastic sampling methods, which suffer from high structural redundancy and incomplete functional coverage. To address this, we introduce an exhaustive dataset of univariate canonical skeletons generated via a deterministic constrained context-free grammar. A canonical skeleton acts as a generic structural representation that subsumes more specific functional forms, eliminating redundant expressions and avoiding repeated computational efforts. Although our dataset consists of univariate skeletons, it is designed to support the decomposable SR paradigm to solve multivariate SR problems without assuming linear separability. Furthermore, we pair this dataset with a sampling strategy that generates clean numerical data without triggering numerical instabilities or relying on artificial protected operators. Canonicalizing two existing neural SR datasets reveals that our dataset is substantially more compact, eliminates structural repetitions, and achieves a uniform operator distribution free of simplicity bias. Finally, we establish a benchmark of 150 SR problems across three tiers, on which state-of-the-art SR methods are shown to struggle significantly.
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cs.LG Maria V. Salvador, Ana F. Sequeira, Jaime S. Cardoso · Oct 14, 2026

The paper investigates when jointly optimizing imputation with a downstream classifier improves robustness under train–test mismatches in missingness rates or mechanisms. Instead of treating imputation as fixed preprocessing, the authors cast missing values as learnable variables regularized around a reference imputation, giving both amortized and latent instantiations. Through 98 tabular classification datasets—and targeted shift experiments on 36 datasets—they show that reconstruction quality is a poor proxy for predictive utility and that task-aware corrections matter most in hard regimes such as MNAR and severe distribution shift.

Missing data is a pervasive challenge in machine learning, often degrading predictive performance and complicating model deployment. Most existing approaches treat imputation as a preprocessing step independent of the downstream task, a separation that becomes problematic under train-test mismatches in missingness mechanisms or rates. We introduce a unified framework that treats missing entries as variables in a task-conditioned optimization problem. We instantiate this framework in two settings: an amortized approach for scenarios with missing data at both training and test time, and a latent optimization approach for settings where only training data is incomplete. The evaluation is conducted on 98 tabular datasets, and robustness under train-test mismatches is assessed on 36 datasets. Results reveal that reconstruction error constitutes a poor proxy for predictive utility (Spearman rho approximately 0.16 to 0.32), and that task-aware imputation becomes critical in scenarios where classical methods fail to recover complete-data performance, achieving win rates of up to 80% in challenging train-test mismatch scenarios.
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cs.CGcs.CCcs.LG Ditbul Ban, Younghun Roh, Julian Shun et al. · Oct 14, 2026

Most standard diversity measures violate at least one of the Mironov–Prokhorenkova axioms (monotonicity, uniqueness, continuity), and the only known measures that satisfy all three are NP-hard to compute. This paper introduces Geometric Kernel Diversity (GKD), which defines diversity as the volume of the union of radial-kernel under-graph solids for a point set in Euclidean space. For a canonical Student-$t_2$ kernel, the authors prove that GKD satisfies all three axioms on Euclidean-realizable inputs, give exact polynomial-time algorithms for dimensions $d \leq 3$, and provide a randomized $(1\pm\varepsilon)$-approximation for arbitrary dimensions. The contribution is a theoretically clean first positive answer in the restricted Euclidean setting, though the axiomatic question on general distance matrices and exact computation in $d \geq 4$ remain open.

Quantifying the diversity of a set of objects is a fundamental problem in machine learning and statistics. Mironov and Prokhorenkova (2025) recently showed that three axioms-monotonicity, uniqueness, and continuity-are crucial for a reliable diversity measure and that none of the standard metrics in the literature satisfy all three. They also constructed two measures that do satisfy the axioms, but both are NP-hard to compute, leaving open the question of whether efficient axiomatic diversity measures can exist. We study a Euclidean-restricted version of this question. We introduce Geometric Kernel Diversity (GKD), which associates a radial kernel solid with each point and measures the volume of their union. We show that canonical GKD satisfies all three Mironov-Prokhorenkova axioms on Euclidean-realizable inputs. For canonical GKD, we give exact polynomial-time algorithms in dimensions $d \le 3$. In arbitrary dimensions, we give a randomized algorithm that returns a $(1 \pm \varepsilon)$-approximation with probability at least $1-\delta$ in time $O \left(\frac{nd}{\varepsilon^2}\log\frac{2}{\delta}\right)$ for $n$ points. The axiomatic guarantee applies to exact canonical GKD; the randomized algorithm approximates this deterministic quantity. We further show that the two diversity measures of Mironov and Prokhorenkova (2025) remain NP-hard on Euclidean-realizable inputs and, unless $\mathrm{NP} = \mathrm{RP}$, admit no FPRAS even on this restricted domain.
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cs.LGstat.ML Dai Shi, Andi Han, Xiaoyu Li et al. · Oct 14, 2026

Conflicting studies on whether neural networks converge to a shared representation have used different alignment metrics and reached opposite conclusions. This paper proposes the Lattice Representation Hypothesis (LRH), which formalizes alignment criteria into a lattice ordered by strength, and argues that disagreements arise because prior work evaluates criteria at different points on this lattice. It also proves in idealized models that the training procedure and objective determine which criteria are met reliably across independent runs, supported by experiments on dozens of pretrained vision and language models.

The Platonic Representation Hypothesis (PRH) holds that increasingly capable models converge toward a common representation. However, recent studies have shown different views on aligning representations via their neighborhoods, spanning trees, and distances. We show that these views can differ because the alignment criteria behind them sit at different points of one lattice, and we formalize this explanation as the Lattice Representation Hypothesis (LRH). Under the LRH, the convergence claimed by the PRH is agreement at the top of the lattice, whereas its evidence comes from neighbor overlap, a criterion near the bottom. The Aristotelian Representation Hypothesis (ARH) restricts convergence to local neighborhoods because calibration keeps the growth of neighbor overlap with model size but largely removes that of centered kernel alignment. We show that this removal can come from calibrating a maximum over layers, so global convergence remains open. Back into Plato's Cave (BPC) infers coarse shared structure from the collapse of neighbor overlap on larger evaluation sets, whereas we trace it at least partly to a fixed number of neighbors covering shorter distances. We show that the spanning-tree overlap used by Structure over Geometry (SOG) mostly repeats one-nearest-neighbor overlap. The LRH also extends to independently trained models, whose training procedure and objective decide the criteria met reliably across runs. We prove this claim for the training procedure in a linear autoencoder and for the objective in a finite contrastive Gibbs model. Experiments on dozens of pretrained vision and language models and thousands of runs of both theoretical models support these conclusions. We hope this work paves the way toward a general theory of representation hypotheses, with a framework to analyze them and compare their evidence. Project page: https://eethanshi.github.io/LRH
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cs.LGcs.CL Minchan Kim, Sungho Bae, Youngjin Kim et al. · Oct 14, 2026

GRPO for long-horizon agents suffers from sparse terminal rewards that yield all-fail rollout groups and zero advantage signals early in training. This paper studies guide-assisted curricula that replay successful reference prefixes before the learner continues, systematically varying the initial position, handoff granularity, and movement rule. Across Qwen3 models from 1.7B to 8B on BFCL and AppWorld, the authors find that starting near task completion and using outcome-informed call-level selection improves independent execution while reducing training cost. The work usefully frames curriculum design as a practical lever for GRPO-based agent post-training.

Group Relative Policy Optimization (GRPO) provides no reward-relative learning signal when all rollouts receive identical rewards. In long-horizon tasks that require multiple interactions, rewards are given only upon successful task completion, making all-fail groups common early in training and limiting opportunities to practice later steps. Guide Assisted GRPO replays a successful reference prefix before the learner continues. We study how initial positions, handoff units, and movement rules affect unassisted task completion. Across three model sizes on BFCL, starting near completion is more effective under a fixed turn-level threshold rule. Finer handoffs alone do not consistently help, but outcome-informed tool-call selection outperforms GRPO on trained and untrained task categories. Guided starts also improve AppWorld success on both evaluation splits. These findings highlight where learning starts and how starting positions move as key curriculum choices.
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stat.MLcs.LG Haowei Wang, Yilin Zheng · Oct 14, 2026

This paper studies noiseless efficient global optimization via Gaussian Process Thompson Sampling (GP-TS) in the frequentist RKHS setting. It proves that standard GP-TS suffers an intrinsic $\sqrt{\log N}$ simple-regret penalty for Mat\'ern kernels, yielding $O(N^{-\nu/d}\sqrt{\log N})$, and proposes Capped Thompson Sampling (GP-CTS), which achieves the minimax-optimal $\Theta(N^{-\nu/d})$ rate using a known RKHS norm bound. The analysis covers both discrete and continuous domains and is notable for matching upper and lower bounds in a non-bandit setting.

Efficient global optimization aims to identify a global optimum of an expensive black-box function within a limited evaluation budget $N$. We investigate the convergence rates of Gaussian process Thompson sampling (GP-TS) under noiseless observations, assuming a fixed objective function in a reproducing kernel Hilbert space (RKHS). For Mat\'ern kernels with smoothness parameter $\nu$ in dimension $d$, we establish a worst-case expected simple-regret upper bound of $O(N^{-\nu/d}\sqrt{\log N})$ for both discrete GP-TS on sufficiently fine grids and its continuous counterpart. For the continuous implementation, we develop a nested-grid argument to control posterior sample paths over the entire domain. We further establish matching lower bounds of $\Omega(N^{-5/2}\sqrt{\log N})$ for both implementations under a fixed one-dimensional Mat\'ern-$5/2$ kernel, demonstrating that the logarithmic penalty is intrinsic to standard GP-TS in this setting. Motivated by this limitation, we propose Gaussian Process Capped Thompson Sampling (GP-CTS), which caps posterior sample paths using a valid RKHS norm upper bound while preserving optimism. This modification successfully eliminates the logarithmic penalty and achieves the minimax-optimal rate $\Theta(N^{-\nu/d})$ for both discrete and continuous implementations.
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cs.LGcs.CL Qinglin Su, Licheng Pan, Zhen Fang et al. · Oct 14, 2026

RM-OPD targets a real bottleneck in generalist reward modeling: training on mixed-domain data with standard RL produces cross-domain interference and sparse outcome rewards, so capabilities like math verification, code review, and safety guardrails cannot coexist without degrading each other. The core idea is a two-stage framework—first cultivate domain-specialist reward teachers via single-domain GRPO, then distill them into one student through routed on-policy distillation, domain contribution reweighting, and criteria context distillation. This matters because it swaps coarse verdict-level supervision for dense token-level guidance, raising the multi-domain performance ceiling for generative judges.

Reinforcement Learning on Mixed-domain preference data (Mix-RL) has become the mainstream approach for training general-purpose Generative Reward Models (GRMs). However, Mix-RL suffers from two critical bottlenecks: the reward sparsity induced by outcome rewards, and the cross-domain interference arising from jointly optimizing heterogeneous capabilities, which together give rise to imbalanced capability acquisition and pervasive reward hacking. Inspired by the success of On-Policy Distillation (OPD) in multi-domain capability integration, we introduce RM-OPD (Reward Modeling via On-Policy Distillation), a two-stage framework that separates specialist acquisition from capability integration. First, we cultivate domain-specialized teacher models via single-domain GRPO fine-tuning, allowing each expert to reach its performance ceiling in isolation; then we consolidate these teachers into one student model through (i) routed on-policy distillation, which provides dense signed token-level supervision on student-generated critiques; (ii) domain contribution reweighting, which reweights token guidance toward target domain shares, preventing specific domains from dominating optimization; and (iii) optional criteria context distillation, which conditions teachers on domain-specific evaluation criteria to sharpen token-level supervision. Across multiple RM benchmarks and two base models, RM-OPD consistently outperforms vanilla Mix-RL and other strong baselines, achieving overall superior performance and exhibiting an emergent &#34;teacher-surpassing&#34; effect. These results establish RM-OPD as a promising paradigm for building generalist GRMs.
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cs.LG Fernando Acero · Oct 14, 2026

Autoregressive transformers trained on limit order book streams are usually evaluated only by output realism, leaving their internal mechanics opaque. This paper inverts the problem by training GPT-style models on synthetic order-flow simulators with known latent parameters, enabling exact verification against Bayes-optimal predictors and oracle entropy floors. It finds that next-token pretraining implements amortized Bayesian inference and online filtering, that latent states are linearly decodable from frozen activations, and that regime diversity—not model scale or token count—drives generalization.

Autoregressive transformers trained on limit order book (LOB) message streams are increasingly proposed as foundation models for market microstructure. Because the generative process of real markets is unknown, these models can be judged only by the realism of their output, leaving open what they actually learn. We make the question answerable by inverting the setup: we train GPT-style models on order flow from simulators whose latent parameters are known, so that the Bayes-optimal predictor, the generating state, and the exact data entropy serve as references. Measured against them, next-token pretraining on order flow implements amortized Bayesian inference over market regimes. The learned predictive matches the exact Bayes optimum to within a millinat per token and approaches the oracle floor even on a nonstationary family whose latent state drifts within an episode, a regime that requires filtering. The latent regime is linearly decodable from frozen activations, well above baselines, so a frozen-model read-out calibrates simulator parameters more accurately than windowed maximum likelihood at a fraction of the cost. In our experiments these capabilities are not produced by scale: capacity and token volume saturate early, and it is the diversity of training regimes, not the token count, that determines generalization to unseen markets. On real NASDAQ data, zero-shot transfer is set by how well the simulator prior covers real flow: an enriched mixture nearly closes the gap to an in-domain baseline, and pretraining beats from-scratch training at every budget across held-out tickers. Known ground truth turns average next-token loss, which is uninformative near the entropy floor, into an exact comparison against the Bayes-optimal and oracle predictors.
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cs.LGcs.CV Miko{\l}aj Pi\'orczy\'nski, Wojciech Masarczyk, Damian S\'ojka et al. · Oct 14, 2026

Multimodal large language models suffer large accuracy drops when their visual inputs are corrupted by noise, blur, or weather artifacts. This paper asks whether test-time feature alignment—matching activation statistics to clean source moments, a technique that works well for CLIP-like classifiers—can recover that lost performance without labels or weight updates. Across three modern MLLMs and 15 standard corruptions, the authors find it cannot: sample-blind, position-shared corrections recover only about one percentage point of an order-of-magnitude larger drop. The core insight is that corruption shifts in MLLM visual token sequences are nearly orthogonal across images and dominate the residual term in a per-token squared-shift decomposition, whereas pooled classification embeddings exhibit a shared, low-rank shift direction. This matters because it establishes that robustness in generative MLLMs is a per-token restoration problem, not a simple domain-statistics-matching problem.

Vision-language models suffer significant accuracy drops under common corruptions. While test-time adaptation (TTA) successfully mitigates these shifts in CLIP-like contrastive models, its application to generative multimodal large language models (MLLMs) remains underexplored and uniquely challenging due to their sequential token generation. In this work, we demonstrate that representation-based TTA fails to recover performance in MLLMs. Our experiments reveal that even when violating standard TTA assumptions by leveraging target data offline, sample-blind feature alignment recovers only marginal accuracy. We attribute this failure to the nature of corruption shifts: unlike CLIP-like architectures, which benefit from a shared domain-shift direction within a single pooled classification embedding, MLLM visual token sequence shifts are nearly orthogonal and span the full embedding space.These findings bound what any sample-blind, position-shared correction at a single encoder site can achieve, establishing that representation-space interventions alone might be insufficient to ensure corruption robustness in MLLMs.
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cs.LG Joshua Cheung, Zhang He · Oct 14, 2026

Latent world models for control are routinely selected and checkpointed by one-step next-embedding prediction loss, on the assumption that lower loss implies better planning. This paper tests that proxy in JEPA architectures by introducing a frozen-decoder protocol that reports one-step error in interpretable physical units, then applies fine-tuning interventions and measures goal-conditioned planning with paired seeds. It finds the relationship saturates after a single epoch within a task and has no stable exchange rate across tasks, implying that latent prediction loss is an unreliable stand-in for planning competence.

Latent world models are routinely selected, checkpointed and ablated on one-step prediction loss, on the assumption that a model which predicts the next latent better is a better model. In model-based RL this assumption is known to be unreliable; we ask whether it also fails for latent world models, where the training target is the model's own embedding and the loss is not expressed in interpretable units. We introduce a frozen-decoder protocol reporting one-step error in physical units, decomposed into the part already present in the encoder's representation and the part the predictor adds. Applying it to a recent end-to-end JEPA world model across three continuous-control environments, we move the metric by fine-tuning and measure goal-conditioned planning on the same checkpoints, with three training seeds and paired planning seeds throughout. Within one environment, a per-epoch ladder shows the relationship saturating after a single epoch: the first epoch improves fidelity by 32% and planning by 4.4 pp, but across the fifteen checkpoints that follow -- a further 15% fidelity improvement, monotone in every training seed -- the correlation between one-step error and planning success is r = -0.010. This is not a task-ceiling artifact: stratifying by a model-independent measure of training-data support, planning in the lowest-support stratum starts at 80%, leaving ample headroom, and is nonetheless flat from epoch 1 onward. Across environments the exchange rate is equally unstable: a 93% fidelity reduction on TwoRoom yields -0.7 pp of planning, while a 40% reduction on PushT yields +4.9 pp [+1.1, +8.9]. All results replicate under a decoder-free measure, latent drift. We also show that a matched continued-training control absorbs the entire fidelity gain we had attributed to an auxiliary objective.