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cs.LG Yusuf Afifi, Artur Kiulian, Anton Polishko et al. · Oct 1, 2026

The paper tackles the frozen-context bottleneck in outcome-based reinforcement learning for forecasting: prior work either pastes fixed research snippets into the prompt before training or lets a frozen model search only at test time, so the policy is never rewarded for gathering better evidence. The authors close this gap by building a multi-turn agentic harness from 2,100+ resolved Polymarket questions, filtering every search and page-read to pre-cutoff information, and training Qwen3.5-35B-A3B with single-epoch GRPO under the Brier-score reward $r=1-(p-y)^2$. The core advance is that the model learns when and what to search for as a temporally grounded skill, rather than optimizing a frozen context window. This matters because it moves forecasting from prompt engineering to genuinely learned research discipline, and the trained open model reportedly beats several frontier systems at roughly 5% of the inference cost.

Outcome-based reinforcement learning can train language models to forecast real-world events, but prior forecasting work either freezes research context before training or deploys agentic research only at test time, so the skill of gathering evidence is never shaped by the reward. We introduce an agentic forecasting environment, dataset, and harness built from 2,100+ resolved Polymarket questions; the agent acquires its own context at rollout time (web search, page reading, and financial time series, all restricted by layered leak filtering to information published before each question's cutoff), and we train Qwen3.5-35B-A3B (3B active parameters) on it with single-epoch GRPO under a Brier-score reward. Training changes how the agent interacts with information: calibration improves 30-40%, and search attempts fall from 3.8 to 2.25 per rollout as evidence discipline is learned. Evaluated in an identical harness against four frontier models, the trained policy also finishes ahead of every frontier model tested at evidence-based forecasting, including Claude Opus 4.5 (soft-Brier 0.254 vs. 0.256, n=265), at about 5% of the inference cost, and its margin is widest on the hardest questions, the ones the crowd itself had not decided. We release the environment, dataset, and per-rollout records as a reusable harness for temporal forecasting agents.
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cs.LG Haocun Ye, Xinlong Jiang, Qile Chen et al. · Oct 1, 2026

Multimodal reinforcement learning with verifiable rewards (RLVR) is widely assumed to improve visual reasoning when models are rewarded for correct answers. This paper exposes a critical gap: benchmark gains can be achieved without learning from images at all, and prolonged training can even erode visual grounding. The authors propose "visual resolvability"—designing tasks where visual evidence is strictly necessary for reward—and show that standard GRPO on carefully constructed counterfactual coordinate scenes drives genuine visual discovery, unlike conventional benchmark training.

Reinforcement learning with verifiable rewards (RLVR) improves vision-language benchmark scores even without visual information during training. With images at test, blind-trained models recover roughly half of the real-image gain at 3B and nearly four fifths at 7B. Prolonged real-image training can erode grounding while benchmark gains persist. Both findings expose the same gap: an image in the prompt is not an image in the learning signal. Our design rule, visual resolvability, asks that visual evidence be necessary for a correct answer and that the task remain learnable. We test it on counterfactual coordinate scenes in which the question stays fixed and the target is never named, so a correct answer requires finding the target in the image. With standard GRPO and correctness-and-format rewards, a 7B model raises its accuracy at finding the target (discovery) from 0.425 to 0.875 on held-out scenes denser than any it trained on, and it improves on question types it never trained on. Two controls locate the source of the gain. Replacing test images with gray canvases drops discovery to zero; training on gray canvases instead, at matched step 30 and in each of four seeds, yields essentially none of the gain even when the model is then tested with real images. The learned skill carries over to grounding tasks built independently of the training corpus. A caption that answers the training question, added to the same images, reward and budget, cuts the gain by nearly two thirds. Changing what reward requires changes what RL learns.
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cs.LG Simon Forbat, Rainer Gemulla · Oct 1, 2026

Relational learning with tabular foundation models currently relies on Deep Feature Synthesis (DFS), which flattens multi-table schemas into single tables via column-wise aggregations along meta-paths. This paper identifies two critical limitations of DFS—feature explosion and interaction blindness—and proposes RelICL, a training-free method that instead propagates row embeddings through the schema graph using the foundation model itself. By iteratively pooling and fusing embeddings, RelICL keeps the TFM-agnostic benefits of DFS while scaling to complex schemas and capturing cross-column interactions. The experimental study on 21 RelBench tasks shows RelICL matches state-of-the-art DFS approaches, though it does not dominate them outright.

Tabular foundation models achieve state-of-the-art performance on single-table tasks without any training. Recent work suggests that they are also well-suited for relational learning via deep feature synthesis (DFS), which flattens a relational schema into a single table by adding aggregates of the other tables' columns as features. This approach is appealing because it directly benefits from improvements to or customization of the underlying tabular foundation model. In this paper, we identify two key problems with DFS: feature explosion and interaction blindness. The first problem arises because the number of DFS features grows quickly as the schema becomes more complex, limiting scalability and performance. The second problem arises because column-wise aggregates do not account for feature interactions, limiting performance. We propose and explore an alternative method termed RelICL, which keeps the benefits of DFS but alleviates these two problems. At its heart, RelICL propagates and fuses information step by step through the schema graph, using the same tabular foundation model that is eventually used for prediction to do so. In our experimental study using RelBench tasks, RelICL was on par with the strongest approach based on deep feature synthesis.
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math.STcs.LGstat.ML Shivam Kumar, Nabarun Deb · Oct 1, 2026

Many applications require sampling from high-dimensional categorical distributions with local dependence, but discrete diffusion models lack end-to-end statistical guarantees. This paper introduces a pinning decomposition of the discrete score under uniform noising, showing that time dependence separates multiplicatively from target dependence for Markov random fields of order $d$. Building on this, the authors design a weight-sharing neural score learner and prove a sample-complexity rate of $\widetilde O_{\mathbb P}(S^d/n)$, replacing the ambient dimension $D$ with the interaction order $d$.

Many applications in statistics, economics, and physics require sampling from high-dimensional categorical distributions with local dependence structures. Examples include finite memory language models, Ising and Potts systems in statistical physics and protein folding, etc. In modern machine learning, discrete diffusions have emerged as a flexible approach for sampling such data, with strong empirical performance. Motivated by this, we develop learning methods with end-to-end sample complexity bounds for discrete diffusion with uniform noising under local dependence, which we model through low order Markov random fields (MRFs). Our main technical insight is a new \emph{pinning decomposition} of the discrete score. It shows that unlike in continuous diffusions, the score decomposes into components where the dependence on time separates multiplicatively from the dependence on the target. Building on this decomposition, we propose a \emph{weight-sharing neural score learner} and combine it with $\tau$-leaping to obtain an end-to-end sampling procedure. Rather than treating score-learning error as a black-box input, as is common in existing sampling analyses, we study the score learning error from finite data and derive optimal sampling guarantees with explicit dependence on the vocabulary size, the interaction order of the MRF, and the sample size. Moreover, our strategy trains a single score network across uniform noise levels while leaving the sampling discretization to be chosen at inference-time. This allows the same trained model to trade accuracy for computational cost as inference-time budgets vary. Numerical experiments on Potts, Ising, and tree-structured models show that weight-sharing score networks outperform fully connected ones for sampling long sequences.
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cs.LG Caleb Stam, Aagrim Hoysal, Sanjukta Krishnagopal · Oct 1, 2026

Graph positional encodings (PSEs) are computed from pairwise edges and inherently miss higher-order interactions such as triangles and cliques. The paper proposes to enrich standard graph models by computing positional encodings on lifted higher-order domains (e.g., clique complexes) and projecting them back to nodes, without altering the backbone. Its core theoretical insight is that lift-induced symmetric node operators can mix the eigenmodes of the original graph Laplacian $L$, placing them outside the class of scalar spectral filters $g(L)$. This yields a principled design rule---the commutator $[L,M] \neq 0$---and an experimental pipeline using Hodge-Laplacian encodings.

Many real-world systems exhibit higher-order interactions among groups of entities that cannot be captured by pairwise relationships alone. Graph Transformers and Graph Neural Networks increasingly rely on positional encodings to enrich graph representations, yet existing positional encodings are computed solely from the original graph and therefore cannot directly capture observed higher-order interactions. Topological Deep Learning addresses this limitation by lifting graphs to simplicial complexes, but typically requires performing message passing or attention on higher-order neural network representations. We introduce a representation learning paradigm that enriches graph representations with higher-order topology through positional encodings, enabling standard graph learning models to exploit lifted incidence structure without modifying the backbone. We derive a theoretical characterization of the expressivity of higher-order positional encodings, proving that node-level operators induced by higher-order lifts can mix graph Laplacian frequencies in ways that scalar graph spectral filters cannot. Guided by this theory, we instantiate higher-order positional encodings using Hodge Laplacians derived from clique complexes. Experiments with Graph Transformers on ZINC and controlled synthetic benchmarks demonstrate improvements in predictive performance, while a fixed-1-skeleton experiment shows that the pipeline can transmit higher-order information when cells are supplied independently of the graph. Together, our results establish higher-order positional encodings as a principled bridge between graph positional encodings and topological deep learning.
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cs.LG Francesco Vitale, Hangli Ge, Francesco Flammini · Oct 1, 2026

Monitoring contact wire geometry is essential to prevent catastrophic failures like pantograph destruction and contact wire breakage in railway systems. Existing vision-based methods track wire height and stagger, but they process these measurements without knowing where along the route they occur. This paper proposes spatially aligning pantograph-catenary telemetry to a GPS master grid, partitioning the route into geographic segments, and training a localized bidirectional LSTM-autoencoder per segment to detect collective anomalies. It targets the blind spot of geographic agnosticism in current industrial monitoring, arguing that location-aware models reduce false positives caused by natural topological variation.

Monitoring the Pantograph-Catenary System (PCS) provides insight into the health conditions of the pantograph and the railway infrastructure. Recent industrial solutions trace the pantograph's contact wire height and stagger (PCS height/stagger) using video monitoring through convolutional neural networks. However, these solutions do not account for the train route's geographic location. Therefore, in this paper we propose a novel framework for 1) localization of the PCS height/stagger by alignment with the nominal GPS coordinates of the reference route, and 2) collective anomaly detection to evaluate the health conditions of the PCS. We apply and assess the localization and detection performance of the methodology to a case-study based on a real-world industrial dataset provided by a railway transportation company, which includes the PCS height/stagger of several train journeys across Italian railway routes.
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cs.LG Zailong Tian, Yanzhe Chen, Zhuoheng Han et al. · Oct 1, 2026

LoRA adapters often suffer from adaptation imbalance, where a handful of singular directions hoard the update energy and hurt both target-task specialization and off-task capability retention. This paper proposes LoRA-Norm, a data-free post-training edit that preserves the learned singular directions but rebalances their gains with a fixed hybrid Newton-Schulz transform and per-module nuclear-norm restoration. The authors argue that learning where to adapt does not ensure that adaptation gains are well balanced, and they evaluate the method on 18 adapters spanning two 8B backbones and three tasks.

While Low-Rank Adaptation (LoRA) enables efficient task specialization, its learned updates can compromise capabilities beyond the target task. We identify \textbf{adaptation imbalance}: a few singular directions dominate the trained update, leaving its performance sensitive to how gains are allocated. We argue that \textbf{learning where to adapt does not ensure that adaptation gains are well balanced}. This motivates \textbf{LoRA-Norm}, a post-training normalization method that retains learned directions while rebalancing their gains. LoRA-Norm combines spectral rebalancing, a fixed nonlinear transformation of singular values, with nuclear-norm restoration, which preserves the original total spectral mass. It requires no calibration data or additional training and introduces no inference overhead. Across two backbones and three adaptation tasks, LoRA-Norm improves average specialization and capability retention, outperforming the evaluated post-hoc spectral pruning and gradient-guided editing configurations on both measures. Stronger functional equalization brings no consistent additional gains, revealing that balancing adapter gains and equalizing their responses are distinct objectives.
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cs.LG Nafiseh Ghoroghchian, Haipeng Zhang, Shuyi Han et al. · Oct 1, 2026

Time series foundation models post strong scores on large benchmarks, yet their grasp of basic temporal logic remains unclear. This paper introduces SimpleTimeBench, a diagnostic suite of univariate and multivariate unit tests for primitives such as linear trends, periodic signals, and deterministic leading-indicator covariates. The authors show that prominent zero-shot TSFMs—including Chronos-2, Moirai, and Toto—fail on several trivial tasks, and that targeted fine-tuning on the full suite yields only marginal gains, suggesting that pre-training scale alone has not bought robust fundamental reasoning.

Despite the success of Time Series Foundation Models (TSFMs) on broad benchmarks, their ability to internalize basic temporal logic, especially in settings supported by exogenous covariates, remains under-examined. We introduce SimpleTimeBench, a diagnostic univariate and multivariate "unit test" suite for primitives such as monotonic trends, periodic signals and leading indicator covariates, scenarios where near-perfect forecasts should be trivial. Surprisingly, prominent multivariate TSFMs (Chronos-2, Moirai and Toto) frequently produce suboptimal zero-shot forecasts for these inputs. While fine-tuning Chronos-2 improves its behaviour on specific tasks, we show that this adaptation degrades performance on other fundamental patterns rather than enhancing its generalizable foundational capabilities. This reveals a gap between pre-training scale and basic temporal reasoning, suggesting that current TSFMs could potentially lack the inductive biases needed to capture simple predictable functions. We further demonstrate that these failures are not merely synthetic curiosities: they persist in real-world sensor forecasting, where TSFMs consistently underutilize leading indicators available in observed covariates. This inability to capture simple relationships limits the practical utility and reliability of current multivariate models.
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cs.LGstat.ML Nam Nguyen, Tuan Quang Dam · Oct 1, 2026

This paper studies fixed-confidence best-arm identification for Bernoulli bandits using the top-two $\beta$-EB-TCI rule, where the challenger is selected by a penalized Bernoulli GLR index. Its core contribution is a sharp non-asymptotic analysis: once the true best arm becomes the permanent leader and its sampling fraction stays near $\beta$, the stopping time is $T_\beta^\star(\mu)\log(1/\delta)$ up to lower-order terms. The paper also identifies exactly where the analysis stalls for the unguarded rule when suboptimal means are tied, and closes the gap with a mild $O(\sqrt{Kt})$ exploration guard.

Top-two algorithms are simple and effective for fixed-confidence best-arm identification, but their sharp non-asymptotic behavior is still not well understood. We study this problem for Bernoulli bandits through $\beta$-EB-TCI, the empirical-best top-two rule of Jourdan et al., whose challenger is chosen using a Bernoulli transportation cost with a logarithmic count penalty. We prove that, after the empirical leader has become the true best arm and its sampling fraction stays close to $\beta$, the stopping time is $T_{\beta}^{\star}(\mu)\log(1/\delta)$ up to lower-order concentration terms. We also show that, in this regime, every challenger is sampled linearly often. Thus, for the original algorithm without forced exploration, the main remaining difficulty is to control when the empirical leader becomes permanently correct. These results imply a non-asymptotic high-probability bound for all Bernoulli instances with a unique best arm. If the algorithm satisfies a finite-mean sufficient-exploration condition, the bound further yields the sharp expected sample complexity. In particular, this gives the sharp expectation result for the unguarded Bernoulli rule when all arm means are pairwise distinct, using the sufficient-exploration result of Jourdan et al. Finally, if we add a mild forced-exploration rule that contributes only $O(\sqrt{Kt})$ pulls up to time $t$, we obtain a self-contained expected sample-complexity theorem for any number of arms under the unique-best-arm assumption. We also identify a limitation of proof strategies that try to handle equal suboptimal means through a single index-comparison argument.
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cs.CRcs.AIcs.LG Emmanuela Andam, Yasir Abbas Zaidi, Abdelali Hadir et al. · Oct 1, 2026

This paper targets few-shot ransomware detection by pairing an Autoencoder Feature Extractor (AFE) with a Model-Agnostic Meta-Learning (MAML) classifier. The idea is to compress 72 tabular behavioral features into a 64-dimensional latent space via the autoencoder, then let MAML adapt a binary classifier from just a handful of labeled malware-versus-benign samples. The authors pitch this as a rapid-deployment defense for healthcare and critical infrastructure settings where new ransomware variants appear with little warning.

Ransomware has emerged as a major cybersecurity threat, with incidents increasing in frequency and impact across critical sectors. These attacks are typically launched through phishing emails, malicious downloads, or exploitation of software vulnerabilities to gain system access. Once inside, the malware encrypts files and demands a ransom, often in cryptocurrency, for the decryption key. Conventional detection methods often struggle with novel or scarce samples, leaving systems vulnerable. To address these challenges, this paper proposes a hybrid deep learning framework that combines an Autoencoder Feature Extractor (AFE) with a Model Agnostic Meta Learning (MAML) classifier for few shot malware detection. The AFE generates compact latent features that reduce noise and dimensionality, while the MAML classifier rapidly adapts to new threats using limited labeled data. Experiments conducted on the Ransomware Dataset 2024 demonstrate the effectiveness of the framework in binary classification tasks. Across one to fifty shot settings, the proposed model consistently achieves high accuracy, F1 score, and Matthews Correlation Coefficient values, maintaining reliable classification even under extreme scarcity. These results highlight the model's robustness and effectiveness in adapting to limited data scenarios, demonstrating the potential of combining feature extraction with meta learning to enhance resilience against malware, particularly in sectors such as healthcare, manufacturing, and public infrastructure, where cyberattacks can cause significant operational and financial disruption.
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math.OCcs.LG Linxuan Pan, Junchi Yang · Oct 1, 2026

Pan and Yang study stochastic nonconvex–strongly-convex bilevel optimization when only unbiased stochastic gradient estimates are available. They propose MRT-FD, a single-loop algorithm that simultaneously tracks the upper-level variable, lower-level solution, and an auxiliary response variable, using order-$p$ finite differences to reconstruct hypergradient actions from first-order queries. For lower-level objectives with order-$p$ smoothness, the method achieves $\mathcal{O}(\varepsilon^{-4-2/p})$ oracle complexity, and the authors prove a matching $\Omega(\varepsilon^{-4-2/p})$ lower bound, settling the optimal $\varepsilon$-dependence for any fixed finite $p$.

We study nonconvex--strongly-convex bilevel optimization under a stochastic first-order oracle. We introduce MRT-FD, a single-loop first-order method that simultaneously tracks the upper-level variable, the lower-level solution, and the auxiliary response arising from implicit differentiation of the hyperobjective. MRT-FD performs one update of each variable per iteration and approximates the second-order derivative actions using order-$p$ finite differences. For any fixed finite smoothness order $p\ge1$ in the lower-level variable, MRT-FD finds an $\varepsilon$-stationary point using $\mathcal{O}(\varepsilon^{-4-2/p})$ stochastic gradient queries. We also prove a matching $\Omega(\varepsilon^{-4-2/p})$ oracle lower bound. The lower-bound construction starts from a hard nonconvex minimization chain with a stronger stochastic oracle, and lifts it to a bilevel problem through a sinusoidal coupling with a scalar lower-level variable. Consequently, the dependence on $\varepsilon$ is optimal for every fixed finite $p$, closing the upper--lower complexity gap in this stochastic first-order oracle setting.
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physics.ao-phcs.LG Alberto Pennino, Francesco Zanetta, Michele Cattaneo et al. · Oct 1, 2026

Varda-single-1.0 is a deterministic, data-driven weather forecasting system built for the Alpine domain, delivering hourly forecasts at 1 km resolution via a stretched-grid Graph Transformer architecture. It combines a 6-hourly autoregressive forecaster with a temporal downscaler to balance forecast horizon and temporal fidelity. The work demonstrates that machine learning models can match or exceed operational numerical weather prediction baselines in complex topography, and it openly releases model weights and software to enable operational adoption and downstream research.

We present Varda-single-1.0, a medium-range data-driven weather prediction system built for the Alpine domain. It provides hourly deterministic regional forecasts on a mesh of 1 km resolution and global forecasts on a 31 km mesh. The system comprises two independently trained stretched-grid Graph Transformer models with encoder-processor-decoder architecture, developed in the Anemoi framework: a 6-hourly autoregressive forecaster and a temporal downscaler reconstructing hourly forecasts between the forecaster's steps. Its training curriculum includes pre-training on ERA5 reanalysis data, followed by training on a 20-year kilometre-scale regional reanalysis, and finally fine-tuning on operational kilometre-scale analyses. Verified over one year against operational analyses and surface station observations, Varda-single is competitive with or improves on MeteoSwiss' operational numerical weather prediction baselines for most headline scores and variables. It broadly matches the skill of the high-resolution 1 km ICON-CH1-EPS control at lead times up to +33 h and generally outperforms the 2 km ICON-CH2-EPS control at lead times up to +120 h. Despite competitive aggregate scores, Varda-single underestimates some local wind maxima and produces overly smooth convective precipitation fields, consistent with the smoothing associated with squared-error training. To gain insight into the model's behaviour, we investigate three case studies beyond the aggregated headline scores, and find particular weaknesses in Varda-single's representation of local winds over complex terrain. Varda-single represents an important step in the development of high-resolution ML forecasting over complex terrain, in complementing the operational regional numerical weather prediction models of MeteoSwiss with data-driven models and in providing a pretrained model for researchers and user-specific applications.
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cs.LG Sibylle Marcotte, Joan Bruna · Oct 1, 2026

This paper asks whether deep self-attention networks can exactly interpolate arbitrary finite datasets using only depth, without adapting parameters to the task. The authors prove that universal interpolation is possible with as few as two frozen Gaussian-initialized single-head residual attention blocks, composed with data-dependent signs, durations, and ordering. They also characterize when causal masking prevents interpolation. The results matter because they provide a theoretical foundation for looped and recurrent-depth transformers that share parameters across layers.

Universal approximation is a necessary qualitative property of learning architectures to benefit from scaling laws. While it is generically verified on a variety of neural architectures and random feature models, it typically involves infinite width limits. In this work, we focus on deep self-attention models and consider instead the `dual' regime, where approximation power is enabled entirely by depth, and featuring strong parameter sharing across layers, motivated by recent models such as the Looped Transformers. More specifically, we ask whether one can find a predefined finite set of parameters, each defining an attention block, such that the resulting finite set of transformations can map any collection of $N$ sequences of $n$ tokens to any other collection of $N$ sequences of $n$ tokens. Crucially, these transformations are \emph{fixed independently of the input and output} collections: only the order in which the blocks are applied, their signs, and their durations depend on the particular interpolation task. Our main result establishes it for residual softmax attention using only two frozen single-head blocks with Gaussian-initialized projection matrices. The result holds at both continuous and finite depth. We also characterize the restrictions imposed by causal masking and establish corresponding universal interpolation guarantees.
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math.OCcs.LG Wei Jiang, Yibo Wang, Wenhao Yang et al. · Oct 1, 2026

STORM is a single-sample stochastic recursive momentum method that avoids periodic full-gradient checkpoints. Prior analyses required a stronger average smoothness assumption and produced suboptimal or logarithmically degraded rates. This paper shows that the original STORM recursion alone achieves the optimal $O(T^{-1/4})$ nonconvex rate, $O(\sigma R/\sqrt{T})$ convex rate, and $O(\sigma^2/(\lambda T))$ strongly convex rate under standard smoothness, by introducing auxiliary sequences and shifted iterates to cancel the estimator bias.

Stochastic recursive momentum (STORM) achieves fast convergence for nonconvex optimization via the variance reduction effect, but existing analyses rely on the strong average smoothness assumption. In this paper, we study the convergence of STORM for different objectives without average smoothness. We first revisit the results under average smoothness, obtaining the $O(T^{-1/3})$ bound for nonconvex objectives and the $O(\sigma^2/(\mu T))$ bound for last-iterate output under the $\mu$-Polyak--\L{}ojasiewicz~(PL) condition. Without average smoothness, we design an auxiliary sequence and compare the STORM update with it in the analysis. With the help of this sequence, we prove that STORM still attains an $O(T^{-1/4})$ rate for nonconvex objectives, which is optimal under standard smoothness. For convex and $\lambda$-strongly convex objectives, we further prove averaged and last-iterate bounds with optimal rates of $O(\sigma R/\sqrt T)$ and $O(\sigma^2/(\lambda T))$, respectively. All the obtained results use the same STORM recursion with different hyperparameter choices.
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cs.AIcs.LG Yaodong Yang, Hongyao Tang, Yi Ma et al. · Oct 1, 2026

Judgment models that return option probabilities without reasoning text are attractive as fast agent policies, but their competence boundary is unclear. This paper argues that such models excel at evaluation (judging given options against described criteria) yet fail at simulation (predicting missing consequences like opponent moves or physical dynamics). By cleanly separating the two, the authors show that supplying simulated outcomes via code restores strong performance across matrix games, text adventures, and robot control. The result is a sharp diagnostic of where fast judgment models can be trusted and a principled architecture for combining them with external simulators.

Judgment models such as \jev{} return, in a single call and without reasoning text, a probability for each described option. This makes them attractive as an agent's action-selection layer, but it is unclear which decisions they can be trusted with. We test \jev{} on reflection tests, one-shot matrix games, the text game ALFWorld and robot control, and find a sharp boundary. \jev{} succeeds when the right option can be judged from what the input describes, which we call \emph{evaluation}. Specifically, it solves 99\% of the counterintuitive Cognitive Reflection Test questions. However, it fails when the right option depends on \emph{simulation} (i.e., predicting something not in the input), such as the opponent's action or the subgoal that must come first. In games, \jev{} plays suboptimally as if its rational opponent acted at random, because the opponent's action is not given. In ALFWorld, \jev{} favors commands that mention an object or place named in the task description. For example, given the task ``put a clean knife in the drawer'', \jev{} carries an unwashed knife straight to the drawer instead of first washing it at the sink. Surprisingly, many of these failures are not due to a lack of knowledge. Asked separately what the opponent will do, \jev{} usually answers correctly, and it responds well given the opponent's action. It fails when one call must both perform the simulation and evaluate based on it. This suggests letting code make the prediction or simulation. When code supplies it, such as a lookahead in ALFWorld and physics simulation in robot control, \jev{} becomes an expert controller through its general evaluation ability.
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cs.LGcs.AI Qijia He, Ruinan Jin, Jun Luo et al. · Oct 1, 2026

Asynchronous LLM post-training mixes stale rollouts from earlier policies, making GRPO-style optimization unstable. This paper derives a convergence bound that exposes a second-moment versus bias tradeoff, then proposes Group-Mass Capping GRPO (GMC-GRPO), which rescales groups when their average importance ratio exceeds a cap. The result is tighter delay dependence than per-trajectory clipping and stronger empirical robustness under large rollout delays on Qwen3 models.

Asynchronous reinforcement learning (RL) improves the efficiency of large language model post-training but introduces stale rollouts generated by earlier policies. Theoretical understanding of how this staleness affects convergence and how to mitigate its impact remains limited. We derive a convergence bound for GRPO-style algorithms that explicitly characterizes the tradeoff between the gradient estimator's second moment and bias. For trajectory-level importance-weighted estimators, our analysis shows that once the second moment is uniformly controlled, delay enters the bound through the bias introduced by clipping or rescaling. Guided by this insight, we propose a novel group mass capping GRPO (GMC-GRPO) method, which minimizes a ratio-based bias bound within a class of weighted estimators sharing a common second-moment guarantee. We establish convergence guarantees for asynchronous GMC-GRPO and show that, compared with TIC-GRPO, it improves the threshold dependence of the fourth-order delay term from $O(\epsilon^{-4})$ to $O(\epsilon^{-2})$ as $\epsilon\to0$, where $1+\epsilon$ is the ratio threshold. Under local policy overlap, the delay-dependent term decreases as $G^{-2/5}$ after tuning the step size, where $G$ is the group size. For fixed behavior and current policies, the bias introduced by group rescaling also vanishes as $G\to\infty$, whereas the bias from trajectory-wise clipping can persist. Experiments across Qwen3 models and reasoning benchmarks demonstrate improved robustness to stale rollouts, with GMC-GRPO achieving the best performance among stable baselines under large rollout delays.
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cs.LG Michael Fore, James Mason Inder, Mrishika Nair et al. · Oct 1, 2026

This paper dissects the group attention mechanism in the time series foundation model Chronos-2, which is advertised to serve both multivariate (MV) and in-context learning (ICL) forecasting. The authors decompose attention into its value/output ($V$/$O$) pooling pathway and its query/key ($Q$/$K$) learned weighting pathway by editing the attention matrix $\alpha$ at inference time. Their core finding is that uniform pooling helps nearly all tested configurations, while learned $Q$/$K$ weighting helps MV forecasting but systematically degrades ICL—sometimes leaving forecasts worse than univariate inference. The work matters because it identifies a cheap, retraining-free fix: forcing $\alpha$ uniform in block 0 alone fully recovers ICL performance across every configuration tested.

Group attention, introduced by the time series forecasting model Chronos-2, attends over the variates of a group at a fixed patch index and serves both multivariate (MV) and in-context learning (ICL) forecasting. Rather than evaluating this cross-variate attention design as a whole, we ask which part of the mechanism earns the benefit and probe its applicability to both MV and ICL regimes. By editing the attention matrix $\alpha$ at inference we separate the two pathways a head comprises: V/O, which projects a weighted summary of the group, and Q/K, which decides the weights. Uniform pooling (V/O without any Q/K weighting) is positive on 18 of our 20 sensor-network configurations, while the learned weighting (Q/K) splits by group type: its contribution is positive or negligible for MV, but materially degrades 8 of the 10 sensor-network ICL configurations, leaving 4 of them worse than univariate inference. By isolating the impact of different layers, we find that uniforming $\alpha$ in the first block alone improves every ICL configuration we test.
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cs.LGcs.CL Xinjian Zhao, Yaoyao Xu, Xuemin Chen et al. · Oct 1, 2026

This paper asks how continuous latent reasoning in chemistry can be improved by training thoughts to anticipate future outcomes without verbalizing every intermediate step. The authors introduce Latent-JEPA, which augments a recurrent latent reasoner with joint-embedding prediction of both textual continuations and molecular structures using pretrained encoders. Evaluated on ChemCoTBench, the framework shows the strongest task gains in molecular optimization and yields latent representations that are more chemically structured.

Large language models offer a promising foundation for chemical reasoning, bringing together chemical knowledge and multistep problem solving. Chemical intuition can provide an initial sense of plausible outcomes before the details of a solution are fully worked out. Inspired by how such expectations complement explicit analysis, we study how continuous latent thoughts can be trained to anticipate informative aspects of future solutions without verbalizing every intermediate step. We introduce Latent JEPA, a framework that combines autoregressive learning with joint-embedding prediction of one or more future views. For chemical reasoning, we develop textual and molecular prediction objectives that connect latent thoughts to both subsequent reasoning and molecular outcomes. Experiments on ChemCoTBench show gains in molecular optimization and on several editing and reaction metrics. Representation analyses show that future prediction makes latent thoughts more informative about molecular outcomes and strengthens their correspondence with chemical structure. These findings support abstract future prediction as a learning principle for connecting continuous latent reasoning with scientific outcomes.
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cs.LG Kevin Tirta Wijaya, Alston Lo, Michael Sun et al. · Oct 1, 2026

This paper tackles validation congestion in scientific discovery, where enormous virtual libraries overwhelm scarce experimental capacity. Instead of relying on data-hungry regressors, it proposes PRISMS, a framework that curates candidates using multi-fidelity pairwise rankings aggregated through a regularized Bradley-Terry model, escalating queries to expensive experts via a Fisher-information criterion. The central claim is that comparative judgments from heterogeneous experts can slash the number of slow experimental rounds needed to find top-performing designs.

Modern computational methods can now propose candidate molecules, materials, and other scientific designs at an unprecedented scale, creating a validation congestion where candidates are abundant, but experimental capacity to physically evaluate them remains scarce. Discovering novel scientific designs has therefore become increasingly dependent on curation: selecting a small set of promising designs for slow and costly experiments. Existing curation methods typically rely on data-driven regression models that predict absolute scores, but training these models requires substantial experimental data to begin with. Yet, useful curation signals do not have to take the form of absolute measurements, as scientific design discovery is often comparative in nature. Here, we propose that curation can instead be primarily driven by expert pairwise rankings, which are substantially easier to gather. The expertise can come from computational tools or human input of multiple levels of fidelity, ranging from empirical rules of thumb to agentic workflows and experienced scientists. We introduce PRISMS, a framework that uses pairwise rankings from one or more experts, potentially spanning multiple levels of expertise, to identify the most promising candidates without relying on data-hungry regressors. When experts differ in fidelity and cost, PRISMS escalates pairwise queries from lower- to higher-fidelity rankers based on a Fisher-information criterion. In iterative screening that selects designs from fixed drug discovery libraries, PRISMS achieves 50% top-10 discovery recall in ~42% fewer rounds than regression-only active learning, and in ~15% fewer rounds than the ranking-based method with no selective escalation. In optimization that generates new designs without restriction to a predefined library, PRISMS achieves ~18.8% higher hypervolume than the Bayesian optimization baseline.
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cs.CLcs.LG Alessandro Turrin, Patrik Okanovic, Torsten Hoefler et al. · Oct 1, 2026

Selecting the best large language model for a live stream of prompts is difficult because benchmark scores are only coarse proxies for real-world performance and oracle annotations are costly. This paper proposes Online LLM Picker, the first active model selection framework designed specifically for LLMs in streaming settings: it uses an Exponential Weights posterior and an adaptive query probability based on hypothetical response variance scaled by posterior entropy to decide which prompts are worth annotating. Evaluated across over 130 models and 10 datasets spanning question answering, dialogue, grammar correction, and math, the method claims to cut annotation cost by up to 71.67% and reduce regret by up to 2.51× compared to baselines.

Large Language Models (LLMs) are increasingly applied to process streaming data, with practitioners relying on benchmarks to select the best model even though these signals only approximate real performance. While oracle annotations can provide reliable feedback, they are often costly and difficult to obtain at scale. To address this challenge, we propose ONLINE LLM PICKER, the first framework for active model selection for LLMs in online settings. Given an arbitrary stream of queries and a limited annotation budget, ONLINE LLM PICKER selects the most informative prompts for annotation to identify the best LLM among candidate models. Across multiple tasks including 10 datasets, for over 130 language models, we show that ONLINE LLM PICKER saves annotation cost by up to 71.67% while reliably identifying the best or near-best model for the stream. We also show that using the returned model for sequential generation on unannotated prompts across the stream reduces regret by up to a factor of 2.51x, indicating that ONLINE LLM PICKER can identify the best or near-best model well before processing all streaming prompts.