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cs.ROcs.AIcs.HC Amr Mousa, Rifny Rachman, Neil Karavis et al. · Oct 1, 2026

Quadrupedal locomotion requires balancing command tracking, stability, and energy efficiency, yet conventional RL bakes these trade-offs into a static scalar reward that cannot change after training. PROMO proposes a preference-conditioned multi-objective framework that takes the relative priority vector $w_t \in \Delta^{K-1}$ with $K=3$ as a runtime input to a single policy, while keeping embodiment-specific locomotion priors fixed. On a Unitree Go2, the same policy transferred zero-shot modulates behavior through preference changes alone, cutting specific energy by up to $30.4\%$, position error by $38.7\%$, and peak body-attitude deviation by $59.0\%$.

Quadrupedal locomotion requires balancing conflicting objectives such as command tracking, stability, and energy efficiency, yet conventional reinforcement learning (RL) hardcodes these priorities into a fixed scalar reward at training time. We present PROMO (Preference-Conditioned Multi-Objective Reinforcement Learning), a semantic multi-objective approach that makes this trade-off an explicit runtime input to a single locomotion policy. PROMO conditions the policy on deployment facing preferences while keeping embodiment-specific locomotion priors fixed, thereby separating operator intent from reward shaping terms required for viable gait generation. Compared with fixed-objective controllers, multi-objective baselines, and independently trained specialists, PROMO achieves objective specialization and robustness from a single deployable policy. Across 100 sampled preferences in simulation, 67 behaviors are non-dominated under exact Pareto dominance, with a mean preference-objective correlation of 0.843, demonstrating broad Pareto coverage and predictable preference response. The same policy transfers zero-shot to a Unitree Go2, where preference changes alone reduce specific energy by up to 30.4%, position error by 38.7%, and peak body-attitude deviation by 59.0% relative to the balanced preference. These results establish preference-conditioned multi-objective RL as a practical runtime interface for adaptive legged locomotion, extending its role beyond offline Pareto-set construction. Open-source code and videos are available at https://amrmousa.com/promo/.
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cs.NEcs.LG Aviral Gandhi, Jinglue Xu, Jialong Li et al. · Oct 1, 2026

LESS introduces a lightweight neural architecture search pipeline that marries a brief fair supernet warm-up with candidate-conditioned hard-path updates inside a CMA-ES loop. The core claim is that just six balanced SGD steps per proposal are enough to sharply reduce selection regret, enabling NAS-Bench-201 searches in roughly seven minutes on a single RTX 4090 without retuning across datasets. If this speed–accuracy trade-off holds more broadly, it could lower the barrier to reproducible NAS experiments.

Low-cost NAS must both explore high-performing architectures and identify them reliably, yet reducing evaluation cost often weakens the fidelity of candidate comparisons. Training-free methods reduce evaluation cost by replacing learned task feedback with proxy signals measured at initialization. We introduce LESS (Lightweight Evolutionary Supernet Search), a data-driven method that combines a brief fair hard-path warm-up with discrete search under a single CMA-ES distribution. Each proposal is evaluated as its decoded hard genotype after six candidate-conditioned supernet updates. On NAS-Bench-201, LESS achieves \(93.189\pm0.467\%\) CIFAR-10 test accuracy in 409.1 seconds, coming within 0.04 percentage points of FairNAS using approximately \(1/24\) of its source-reported search time. Matched controls show that calibration improves selected validation accuracy by \(0.577\) percentage points while changing best-visited accuracy by only \(0.054\) points, indicating that its primary effect is to reduce selection regret. The frozen configuration transfers without tuning to CIFAR-100 and ImageNet16-120 with \(69.615\pm1.139\%\) and \(43.720\pm1.697\%\) accuracy. Applied without tuning to the larger DARTS space, LESS achieves \(96.95\pm0.14\%\) on CIFAR-10 and \(82.43\pm0.80\%\) on CIFAR-100, with each search completing in approximately 43.5 minutes on a single GPU. Together, these results show that short, balanced, data-dependent updates enable competitive neural architecture search across datasets and search spaces within minutes.
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cs.LGquant-ph Bisma Majid, Shabir Ahmed Sofi, Mir Mohammad Yousuf · Oct 1, 2026

This paper studies how to make Quantum Reinforcement Learning (QRL) for combinatorial optimization more robust on near-term quantum devices. Its core idea is APGEM, a LinUCB contextual-bandit controller that dynamically selects among error-mitigation techniques—Zero-Noise Extrapolation, Probabilistic Error Cancellation, Clifford Data Regression, and Readout Error Mitigation—based on a cost-aware utility that balances fidelity gain against shot cost and estimator variance. The work matters because static error mitigation cannot adapt to changing noise regimes or training phases, and adaptive orchestration could improve the reliability of hybrid quantum-classical loops.

Quantum Reinforcement Learning (QRL) integrates reinforcement learning with parameterized quantum circuits and is a promising approach to combinatorial optimization. On Noisy Intermediate-Scale Quantum (NISQ) devices, however, decoherence, gate imperfections, and measurement errors reduce policy quality and make learning less reliable. Existing error mitigation techniques are generally applied as fixed corrections that do not adapt to changing noise conditions or to the evolving state of training. This work presents Adaptive Policy-Guided Error Mitigation (APGEM) as a context-aware orchestration layer of the hybrid quantum-classical training loop that dynamically selects the most suitable mitigation strategy during QRL training. APGEM evaluates Zero-Noise Extrapolation (ZNE), Probabilistic Error Cancellation (PEC), Clifford Data Regression (CDR), and Readout Error Mitigation (REM) using policy-level indicators, including quantum-state fidelity, policy entropy, cumulative reward, and approximation ratio, and integrates the selected strategy directly into the reinforcement learning loop. The framework is evaluated on the Capacitated Vehicle Routing Problem (CVRP), a representative NP-hard problem in urban logistics, under a range of NISQ noise models and noise levels. APGEM consistently outperforms conventional static mitigation methods, reaches approximately 94% of the utility of an oracle strategy, maintains higher quantum-state fidelity as noise increases, and produces more stable learning behaviour throughout training. Ablation studies show that the framework learns context-aware mitigation policies that adapt to different noise environments and circuit execution conditions. These findings demonstrate that integrating adaptive error mitigation into the learning process substantially improves the robustness and reliability of QRL on NISQ hardware.
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cs.LG SeongHyeon Kim, Chaeyun Jang, Seungyoo Lee et al. · Oct 1, 2026

Unified language models must handle heterogeneous capabilities such as mathematics, coding, instruction following, and controllable reasoning, yet standard single-trajectory training is notoriously sensitive to ordering and data ratios. Naive weight-space merging of single-objective experts offers a modular alternative but often collapses distinct behaviors or degrades cross-domain performance. This paper proposes Mixture-Trained Merging (MTM), which trains each branch on an objective-biased data mixture rather than a pure objective so that the branches stay in mutually compatible regions of parameter space and can be merged at deployment time.

Unified language models are increasingly expected to combine heterogeneous capabilities, such as mathematics, code, instruction following, and controllable thinking behavior, within a single set of parameters. A common solution is sequential post-training on multiple objectives, but this entangles all objectives along one optimization trajectory and makes the final model highly sensitive to training order, data ratios, schedules, and stopping criteria. Weight-space merging offers a modular alternative, but naive merging of single-objective experts often fails: domain capabilities degrade sharply, or think/non-think modes collapse into one dominant behavior. We attribute both failures to incompatible weight-space geometry: experts trained on single objectives drift to distant regions of parameter space, placing their interpolations outside any shared low-loss basin. We propose Mixture-Trained Merging (MTM), which trains each branch on an objective-biased data mixture rather than a single objective, exposing it to cross-objective interactions and making branches compatible at merge time. MTM uses merged-model evaluations as a low-cost signal for selecting branch mixtures, avoiding expensive data-mixture ablations. The procedure is iterative: each round promotes the base model using globally selected merge coefficients and refines each branch mixture using domain-preferred coefficients under constraints that preserve other objectives. To scale beyond simplex grid search, MTM uses qNEHVI-based multi-objective Bayesian optimization. Across code, mathematics, instruction following, and think/non-think control, MTM outperforms naive merging and preserves behavioral separation where single-objective merging collapses, suggesting that effective unified models require branches trained to be mergeable.
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cs.LGcs.AI Assaf Ben-Kish, Akarsh Kumar, James Glass et al. · Oct 1, 2026

Catastrophic forgetting remains a critical barrier in multi-phase training of large language models. This paper recasts forgetting as a geometric phenomenon at the level of each weight matrix: standard gradient updates act on all inputs, not just those from the new task, corrupting prior mappings. The authors propose Local Support Learning (LSL), which pairs task-specific adapters with per-matrix Gaussian Mixture Model gates that restrict updates to activations near the current training distribution. Empirically, LSL retains pretrained math, coding, and instruction-following capabilities in models up to 7B parameters while learning new domains efficiently.

We explore catastrophic forgetting in the context of large pre-trained models. By considering forgetting as a geometric problem in the input space of each weight matrix, we uncover a natural retention objective under which updates produced by gradient-based optimizers are suboptimal. Following this observation, we propose Local Support Learning (LSL), a general-purpose framework that augments gradient-based training for retention of prior capabilities without access to prior data. During a new learning phase, LSL pairs two components with distinct roles: a standard weight adapter, trained as usual to minimize the loss, and a gating function that enables the adapter only on input activations from its own training distribution, making the update local to that distribution. The key challenge is that this gate must route data from all learning phases while training only on data from the current one. We address this with a gate based on a Gaussian Mixture Model (GMM), whose likelihood decays rapidly away from its training data, giving it a natural tendency to stay closed on data from prior phases. We show that this post-training approach can resolve forgetting in LLMs of up to 7 billion parameters, retaining both pretrained and finetuned capabilities across multiple training phases, while being efficient in memory and compute, robust to hyperparameter choice, and showing scaling potential.
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cs.LGcs.AIcs.RO Sebastian Sanokowski, Alireza Sarmadi, Majid Khadiv · Oct 1, 2026

Policy-gradient methods suffer from high variance, while pathwise actor updates require accurate action derivatives that standard value-function training does not guarantee. FERPO addresses this by deriving an entropy- and KL-regularized target action distribution from critic values alone, then fitting the policy with forward KL via self-normalized importance sampling---never differentiating the critic with respect to actions. The method targets massively parallel on-policy robot learning, where reliable policy improvement is critical for both sample and wall-clock efficiency.

Several state-of-the-art methods for online reinforcement learning in continuous control improve policies using action gradients of a learned critic. However, critics are typically trained to predict returns, and accurate value predictions do not necessarily yield accurate action derivatives, potentially leading to unreliable policy updates. We propose Forward Entropy-Regularized Policy Optimization (FERPO), an on-policy maximum entropy reinforcement learning algorithm that performs policy improvement using critic values without differentiating the critic with respect to actions. FERPO derives an optimal target action distribution from a policy-improvement objective regularized by entropy and Kullback-Leibler (KL) divergence. We then fit the actor to this target by minimizing a forward-KL objective, estimated using self-normalized importance sampling (SNIS) with actions drawn from the rollout policy. By limiting the target distribution's deviation from the rollout policy, the KL regularization helps keep these importance weights well behaved. In contrast to reverse-KL objectives, which can favor a subset of the target distribution's modes, the forward-KL objective encourages coverage of multiple high-value modes and thereby promotes exploration. Experiments and ablations on MuJoCo Playground and ManiSkill show competitive performance and sample-efficiency gains. Computational benchmarks also demonstrate faster actor updates than Relative Entropy Pathwise Policy Optimization (REPPO).
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cs.CVcs.AIcs.CL Sophia Sirko-Galouchenko, Monika Wysoczanska, Andrei Bursuc et al. · Oct 1, 2026

Where-OPD proposes a new on-policy self-distillation paradigm for multimodal large language models. Instead of giving the teacher zoomed-in image crops, it provides textual spatial hints that identify question-relevant visual elements and their coordinates, using procedurally generated synthetic counting scenes where object locations are known by design. The student learns to match the teacher’s behavior from the raw image and question alone, and the authors claim that training on just 3,000 such synthetic scenes transfers to broad real-world perception gains across 15 benchmarks.

On-policy self-distillation has recently emerged as an effective approach for improving language-model reasoning by supervising students with a frozen or EMA version of themselves that receives privileged information. Its application to multimodal large language models (MLLMs), however, remains largely unexplored. Recent approaches use privileged visual information, such as image crops corresponding to a question, to improve fine-grained perception, but their gains are confined to tasks that benefit from such visual zooming and require either human-annotated grounding data or external teacher models. We introduce a different form of on-policy self-distillation for MLLMs that provides the teacher with textual, spatially grounded guidance identifying the visual elements relevant to a query. We use procedurally generated scenes with automatically available object identities and spatial coordinates, enabling scalable and annotation-free post-training. The teacher uses this spatial guidance to locate and integrate evidence from multiple relevant image regions, while the student learns to reproduce the resulting behavior from the image and question alone. Our approach consistently improves performance on counting, document and chart understanding benchmarks across multiple models. Importantly, although post-training uses only synthetic scenes, the resulting improvements transfer to real-world perception benchmarks, yielding a 3.23-point gain in average performance across CVBench, V*, ZoomBench, BLINK, HR-Bench, and MME-RealWorld. These results show that spatially grounded privileged information can induce broader perceptual capabilities through on-policy self-distillation, enabling substantial synthetic-to-real transfer beyond the task and data distribution used for post-training. Project page: https://github.com/sirkosophia/Where-OPD
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cs.LG Akshay Balsubramani · Oct 1, 2026

The paper solves the generalized Schrödinger bridge on finite graphs—transporting probability mass between distributions while charging costs for visited states—by showing that state costs fold into the reference process via a Feynman–Kac tilt. This reduces the problem to solving a plain bridge against the tilted generator $A = Q - \operatorname{diag}(f)$ with sparse matrix-exponential iterations, eliminating the need for learned controls or tuned temporal-difference penalties. The method scales to millions of nodes and extends to congestion costs through a provably convergent damped best-response outer loop.

The generalized Schr\"odinger bridge on a graph moves mass between two distributions while charging a cost for the states visited. It has been approached by learning the rates of a controlled continuous-time Markov chain, with a temporal-difference penalty that restores the cost. A state cost folds into the reference process as a Feynman-Kac tilt. The cost-augmented bridge is then a plain bridge against the tilted reference, and the penalty is unnecessary. The bridge is computed exactly by alternating two endpoint rescalings, each one sparse matrix-exponential application; nothing is discretized in time or learned. The alternation converges at a rate set by the endpoint coupling alone. For a quadratic congestion cost on time-averaged occupancies, damped best response around the exact bridge is gradient descent on a strongly convex function, and its residual bounds its error. On a protein-folding model, a free-energy cost lowers the expected barrier of the folding paths. On the learned approach's road network, roll-outs of the exact bridge match the target within sampling error, and on networks with millions of intersections its memory grows linearly.
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cs.CLcs.AIcs.LG Hui Ren, Zihan Li, Chang Liu et al. · Oct 1, 2026

Hierarchical Continuous Diffusion Language Models tackle a core bottleneck in non-autoregressive generation: discrete diffusion decodes parallel tokens as independent marginals, while continuous diffusion lacks valid token anchors until the final step. The authors propose HC-DLM, a hierarchy where a continuous latent trajectory is the sole persistent state and tokens are read out and fed back at every step to scaffold the next latent update. A single variational bound yields the training objective, and experiments span structured reasoning, mathematical planning, and language modeling.

Discrete diffusion language models offer a compelling alternative to autoregressive generation for tasks demanding bidirectional reasoning and global constraint satisfaction. Yet they share a structural bottleneck: when decoding in parallel, each token is sampled independently from its marginal, severing the statistical dependencies among the tokens decoded together. Continuous diffusion language models avoid this by denoising a shared continuous state, but their denoiser sees only that state, so nothing ties it to a valid token configuration until it is finally decoded. To address this, we propose Hierarchical Continuous Diffusion Language Models (HC-DLM), which couple discrete token generation with a continuous latent trajectory in a single, principled denoising process, whose training objective is derived from a variational bound on the token likelihood. In contrast to recent methods that attach continuous context to a self-contained discrete chain, HC-DLM makes the latent the only persistent generative state: tokens are read out from it at every step and feed back as a scaffold for the next latent update. On structured reasoning (Sudoku), mathematical planning (Countdown) and language modeling (LM1B), HC-DLM improves over discrete and continuous diffusion baselines at matched model size, in puzzle accuracy on Sudoku and Countdown and in generative perplexity on LM1B. Project page: https://hc-dlm.github.io/.
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cs.LGcs.AI Jinhwan Sul, Panagiotis Theodoropoulos, Vincent Pacelli et al. · Oct 1, 2026

Schrödinger bridge (SB) transport assumes a fixed initial distribution, which breaks at test time when inputs shift. This paper introduces Distributionally Robust Schrödinger Bridge (DRSB), which learns a single controller by minimizing the worst-case sum of control energy $\int_0^1 \frac{1}{2}\|u_t^\theta(X_t)\|^2 dt$ and a terminal KL penalty $\rho \mathrm{KL}(p_1^{u,\mu}\|\nu)$ over an ambiguity set $\mathfrak{M}_\epsilon(\hat{\mu})$ of initial distributions. The authors derive a variational reformulation, connect it to stochastic optimal control and distributionally robust optimization, and develop Wasserstein and Sinkhorn variants with alternating block updates. Experiments on 2D transport and FFHQ image-to-image translation show improved robustness to input perturbations, with a tradeoff in nominal performance.

Schr\"odinger bridge (SB) learns stochastic transport between prescribed initial and target distributions. When the initial distribution shifts at test time, the learned dynamics can fail to recover the target distribution. We introduce the Distributionally Robust Schr\"odinger Bridge (DRSB), which learns a single controller that accounts for uncertainty in the initial distribution. The DRSB objective consists of control energy and a KL penalty between the resulting terminal distribution and the target distribution. DRSB seeks a single controller that minimizes the worst-case value of this objective as the initial distribution varies within an ambiguity set around the nominal distribution. We derive an exact variational formulation of this objective and connect its fixed-terminal-cost subproblem to stochastic optimal control and distributionally robust optimization. This formulation motivates an alternating algorithm that updates the adversarial initial distribution, estimates the terminal log-density ratio, and trains the controller. We develop Wasserstein and Sinkhorn variants using stochastic control optimality conditions to approximate the gradients required for adversarial updates. Experiments on two-dimensional transport tasks and image-to-image translation show improved robustness to input perturbations relative to standard SB, with a tradeoff in nominal performance. On Gaussian mixture transport, Sinkhorn DRSB also achieves lower mean sliced Wasserstein distance than fixed-level noise augmentation at both tested unseen noise levels.
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cs.CVcs.LG Faias Satter, Sk. Md. Masudul Ahsan · Oct 1, 2026

This paper tackles handwritten Bangla word recognition by casting it as character-level object detection rather than whole-word classification. The authors ensemble SSD-MobileNetV2 and Faster R-CNN-InceptionResNetV2 to spot individual characters and diacritics in unsegmented word images, then rearrange the predictions into text. They introduce a modified Non-Maximum Suppression and a heuristic called Preserving Necessary Overlap (PNO) to cope with the cursive matra line and overlapping diacritics that make Bangla OCR notoriously difficult.

An optical character recognition (OCR) can scan a paper and extract text using technology, making people's jobs easier. While various OCR systems are available in the software industry, finding a reliable equivalent solution for Bangla takes much work. When it comes to handwritten texts, the situation is much more unusual. Recognizing words from word images is the most critical stage in any OCR process. It is the second stage after segmenting words from text pictures. If this stage fails, the overall performance of the OCR will be poor, regardless of how well the other phases perform. This study aims to recognize words using deep learning in a handwritten Bangla word image. Three object detection models, SSD with MobileNetV2, Faster R-CNN with InceptionResNetV2, and an ensemble model of these two, have been used to train and test handwritten word images. A modified Non-Maximum Suppression has been introduced to enhance the effectiveness of the models' results. A customized dataset of 9841 handwritten Bangla word images has been compiled, featuring diverse handwriting styles from various individuals. All three models' performances have been checked against the test dataset, and the ensemble model has been the most impressive, with an F1-score of 92.61%. Also, at the word level, the ensemble model correctly recognizes 96.12% of the words to some extent. The system can be further improved by introducing a post-processing phase to correct errors generated by the system.
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cs.LG Shuo Xing, Zilin Dai, Chengyuan Qian et al. · Oct 1, 2026

LLMs can hit high accuracy on hard math problems while lacking genuine structural insight. This paper proposes the Mathematical Primitive---a concise, non-procedural statement of the key idea that makes a solution possible---and introduces Prim, a benchmark that disentangles structural understanding from procedural execution across Discovery, Generation, Digestion, and Execution. The authors show that independent Discovery is the dominant bottleneck and introduce Absorb, a primitive-privileged self-distillation framework that selectively transfers structural guidance into the student model without requiring primitives at inference time.

While Large Language Models (LLMs) have demonstrated striking capabilities on frontier mathematical problems, it remains unclear whether they possess the structural mathematical understanding underlying their solutions. In this paper, we take a first step toward systematically studying mathematical understanding in LLMs, from diagnosing its distinct capabilities to leveraging these findings to improve post-training. First, we introduce the notion of Mathematical Primitive to probe structural mathematical understanding and propose \hlei{}, a novel benchmark that evaluates mathematical reasoning along four distinct dimensions: Discovery, Generation, Digestion, and Execution. Second, our systematic diagnosis shows that solution accuracy masks distinct capability profiles, primitives unlock substantial latent execution capacity, and Discovery is the dominant bottleneck in mathematical reasoning. Our post-training analysis further shows that discovery-limited failures are particularly amenable to repair. Finally, building on these findings, we introduce \abs{}, a primitive-privileged self-distillation framework that selectively transfers primitive-guided reasoning into the student model. Extensive experiments demonstrate that \abs{} consistently improves mathematical reasoning over baselines across model scales and challenging benchmarks.
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cs.LGcs.AIcs.CL Yafei Zhang, Songshuo Lu, Sicong Liao et al. · Oct 1, 2026

CARM targets off-policy drift in LLM reinforcement learning by preventing signed token log-ratios from canceling in sequence-level response masks. The core idea is to average absolute log-ratios rather than signed ones, which stops bidirectional policy drift from being hidden by the geometric mean. It also proves a joint bound on the fraction and severity of out-of-band token ratios for any accepted response. The method is evaluated on Qwen3.5 models and shows consistent gains over geometric-mean and token-level baselines.

Recent years have witnessed the rapid adoption of reinforcement learning (RL) in large language model (LLM) post-training, with substantial gains in mathematical reasoning and code generation. In practical systems, however, policy updates and differences between rollout and training engines can make sampled responses off-policy. Sequence-level masking addresses this mismatch by deciding whether an entire response should contribute to optimization. A common masking rule uses the length-normalized geometric mean of sampled token probability ratios. Its signed log-ratios can cancel across positions, concealing substantial bidirectional policy drift. We propose \emph{Cancellation-Aware Response Masking} (CARM), a sequence-level mask that takes the absolute value of each token log-ratio before averaging, preventing opposing probability changes from canceling. We prove that accepted responses satisfy a joint bound on the fraction of sampled-token ratios outside a prescribed band and their mean log-distance beyond its boundaries. Experiments on mathematical reasoning and code generation show that CARM improves mean@16 averaged over AIME 2024/2025/2026 and BeyondAIME by up to $3.13$ percentage points over geometric-mean masking, and increases average pass@1 across four code benchmarks by $2.88$ points over the strongest evaluated baseline. These findings support CARM as a theoretically grounded and effective method for response-level off-policy control in LLM reinforcement learning.
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cs.LG Chuqin Geng, Li Zhang, Haolin Ye et al. · Oct 1, 2026

Mechanistic interpretability tries to identify sparse circuit subgraphs that explain model behavior, typically evaluating candidates via intervention-defined faithfulness. This paper demonstrates that faithfulness objectives can prefer an equally sized circuit that reproduces intact-model behavior worse than an alternative, because ablating excluded components distorts the computational context of retained ones. The authors argue this creates an objective-level recovery gap: better discovery algorithms cannot recover true mechanisms if the evaluation metric itself systematically rewards the wrong candidate.

Mechanistic interpretability aims to recover the internal computations responsible for model behavior. Progress in automated circuit discovery is often framed as a search problem: better attribution or optimization should identify better mechanisms. This assumes that the evaluation objective can recognize a better circuit once it is found. We show that intervention-defined faithfulness can instead prefer an equally sized circuit that reproduces the model's behavior less well, creating an objective-level recovery gap. Across four human-reference tasks and InterpBench, we compare validation faithfulness with behavior on held-out prompts under fixed ordinary resampling. The behavioral criterion is agreement with the intact model, including its mistakes, except on Greater-Than, where we use semantic accuracy. Controlled reference edits reveal misranking without any discovery algorithm, and outputs of EAP, EAP-IG, ACDC, and Edge-SP exhibit the same failure. Under resampling, KL misranks 9.4%-41.2% of candidate pairs across these methods on the human-reference tasks. We investigate context distortion as an explanation: replacing excluded signals changes the inputs on which retained components operate. Restoring selected signals from the recipient's intact-model execution repairs 96 of 100 persistent KL misrankings from the discovery pool on both validation and held-out prompts. The circuits and their original behavioral scores remain unchanged. These findings show why better discovery alone is insufficient when its objective rewards the wrong candidate.
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cs.CVcs.AIcs.HC Ramazan Fazylov, Stamatis Lefkimmiatis, Ivan Laptev · Oct 1, 2026

While 3D Gaussian avatars render photorealistic humans efficiently, their animation pipelines are often throttled by costly per-frame neural inference. This paper introduces GALA, which shows that the animation outputs of diverse pretrained avatar networks can be closely approximated by an identity-shared linear blendshape basis extracted via distillation, coupled with a shallow coefficient predictor. By constructing the basis with block-local PCA under a rendering-aware metric and a strict memory budget, the method reduces CPU animation cost by up to three orders of magnitude and enables 60 fps on mobile devices with only modest quality loss.

3D Gaussian avatars support fast rendering, however, their real-time animation is often challenged by the costly neural inference. We address this bottleneck and show that the animation of pretrained avatar models can be closely approximated by a linear combination of identity-independent blendshapes. Building on this finding, we introduce GALA (Gaussian Animation via Linear Approximation), a distillation method that replaces per-frame heavy neural decoding with a shallow coefficient predictor and a linear blend. To improve fidelity and reduce memory requirements, we propose to construct the basis using block-local PCA under a rendering-aware metric and a memory budget. Our method learns a shallow MLP network to predict blendshape coefficients and applies to various animation architectures without retraining original models. We validate GALA by accelerating the inference of three distinct avatar models for 3D animation of facial expressions and full-bodies with clothing dynamics. Across these models, our distillation generalizes to held-out identities and reduces CPU animation cost by up to three orders of magnitude while preserving most of the rendering quality. Excellent results of our method confirm the shared linear structure of learned avatar representations and enable highly efficient and accurate animation at frame rates reaching up to 60fps on mobile devices. Project page: https://ramazan793.github.io/gala/
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cs.LG Yidi Wang, Yunhe Zhang, Bangchao Deng et al. · Oct 1, 2026

Most trajectory generators require check-ins from the deployment city, which is unrealistic when only a public POI map is available. This work studies target-trajectory-free generation: synthesizing human mobility in a new city using only source trajectories and the target city's POI coordinates and categories. Its key insight is to replace absolute destination prediction with transferable relative transitions—semantic and geographic displacements between place contexts—and ground them onto the target POI graph via a behavior graph and an exploration–return walk. This factorization yields a theoretically principled and empirically evaluated method for zero-shot mobility synthesis.

Individual mobility trajectories support urban analysis and location-based services, yet most trajectory generators require observations from their deployment city. This assumption excludes precisely the cities where trajectories are unavailable even though points of interest (POIs) and their attributes can be obtained from public maps. We study target-trajectory-free generation: learning from POIs and trajectories in source cities while utilizing only POI coordinates and categories in a target city, with no target trajectory or trajectory-derived statistic available for training, model selection, or generation. Existing trajectory generators typically predict absolute destinations, entangling reusable movement behavior with city-specific POI identities and spatial layouts. Our core insight is to replace this city-bound output with context-conditioned relative transitions. We propose Nomad, a transfer-and-ground framework that separates learning how people move from determining where those movements are realized. Specifically, a history-conditioned flow-matching model learns from source trajectories a transition prior over semantic displacement between POI contexts, geographic displacement, and elapsed time; at inference, a behavior graph and an exploration--return walk ground sampled transitions onto the target POI map. This factorization enables a direct test of representation level transferability without assuming invariance of the full mobility distribution. Extensive experiments across ten cities and 14 transfers show that Nomad outperforms adaptation baselines in trajectory fidelity and downstream utility, lowering the average error over the best baseline of each metric by about 15% in distributional fidelity and about 3% in downstream utility.
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cs.LGcs.CL Yohan Chatelain (1), Pablo de Oliveira Castro (2) ((1) Krembil Centre for Neuroinformatics, CAMH et al. · Oct 1, 2026

The paper asks whether stochastic rounding (SR) can improve low-precision transformer inference over round-to-nearest (RN), and shows that the benefit is site-dependent: SR outperforms RN in long MLP reductions because its $O(\sqrt{n}u)$ probabilistic error envelope beats the $O(nu)$ deterministic drift of RN, while RN is superior at the language-model head because SR's non-uniform variance is heavily penalized by the Fisher-weighted cross-entropy. The authors support this with a fast variable-precision emulation tool (PRISM), a vector Bienaymé–Chebyshev bound, a second-order loss decomposition, and experiments on DistilGPT-2 that motivate mixed-precision rounding recipes.

Should low-precision transformer inference use stochastic rounding (SR) or round-to-nearest (RN)? The answer depends on where in the network you look. We isolate this effect by holding the numerical format fixed and varying only the rounding rule at individual operation sites. To enable experiments at freely chosen precisions, we extend the PRISM vectorized rounding library to arbitrary virtual precision via a variable-precision stochastic rounding (VPSR) algorithm, proving that the rounding decision is evaluated exactly in hardware floating point. We develop two analyses providing complementary insight into this site-level trade-off. First, a probabilistic forward-error bound for linear projections shows that SR's error envelope grows as $O(\sqrt{n} u)$ in reduction length $n$, versus $O(n u)$ for RN, a gap that widens rapidly at low precision and is most pronounced in the long multilayer perceptron (MLP) down-projection. Second, a second-order decomposition of expected cross-entropy loss change at the output softmax into signed drift, drift curvature, and a Fisher-weighted variance penalty reveals why the two sites behave oppositely: MLP noise is predominantly a uniform logit shift to which softmax is invariant, so SR's variance is largely discounted; head noise is non-uniform across the vocabulary and is not. On DistilGPT-2 at $t=6$ significand bits, observations match theory: SR in the MLP raises perplexity to 1.15x the full-precision reference, versus 2.21x for RN. At the language-model head, the ordering reverses because SR introduces non-uniform variance, whereas deterministic RN carries none. In a mixed-precision configuration (MLP output at $t=6$), assigning SR to the MLP and RN to the head brings perplexity within 1.10x of the full-precision reference, a 28% reduction over matched-bit RN.
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cs.CLcs.AIcs.LG Zilin Du, Bowen Yang, Boyang Albert Li · Oct 1, 2026

Training-data selection for LLMs is usually heuristic or sample-specific, which prevents generalization to unseen data. This paper tackles the harder problem of learning a shared meta-network that scores any example, and shows that plugging such a network into the standard bilevel objective (ScaleBiO) causes unstable optimization and poor transfer. The authors trace the failure to two properties of the ScaleBiO loss—competitive weight suppression and easy-feature dominance—and propose TESS, a method that replaces the bilevel objective with a simple pointwise MSE regression on pseudo-labels derived from loss gaps. TESS achieves strong transfer across datasets, corpus scales, and model sizes while cutting peak memory by over 20%.

Data selection is critical for training large language models on massive and heterogeneous corpora. Meta-learning for Training-data Selection offers a principled alternative to heuristic scoring by learning data weights from a target validation objective, but existing methods face a trade-off between fine-grained valuation and transferability to unseen data. A natural solution is to replace per-sample weights with a selection network. However, we find that directly incorporating such a network into existing MTS objectives leads to unstable optimization and poor generalization, caused by weight suppression and persistent reliance on easy-to-learn features. To address these issues, we propose Transferable Example Scoring and Selection (TESS), a scalable data-selection framework built on a Pointwise Value Matching objective (PVM). Experiments on LLM safety and targeted instruction tuning demonstrate strong transfer across datasets, from subsets to full corpora, and from smaller to larger models.
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cs.LGcs.AI Michael Sullivan, Alexander Koller · Oct 1, 2026

Recent reasoning models show impressive capabilities thanks to RLVR post-training, but their chain-of-thought traces increasingly drift into unusual, non-standard language. This paper formally proves that RLVR optimization allows unbounded language drift while supervised fine-tuning imposes a hard finite bound, and shows empirically that such drift arises specifically when RLVR must discover novel behaviors on tasks beyond the base model's existing capabilities. The results suggest a fundamental tension: improving chain-of-thought monitorability by constraining drift necessarily limits the expected reward a model can achieve.

Recent advances in LLM reasoning models---driven primarily by the paradigm of post-training via reinforcement learning with verifiable reward (RLVR)---have enabled them to accomplish impressively complex tasks. However, in parallel with their rising capabilities, LLMs have increasingly displayed signs of language drift in their chains of thought (CoTs): unusual, non-standard, and seemingly nonsensical language use. Although it is well-documented---and can potentially impair CoT monitorability---the causes of language drift are thus far poorly understood. In this paper, we identify the conditions under which language drift occurs: we prove theoretically that RLVR optimization pressure permits unbounded language drift, while supervised fine-tuning does not. We then show empirically that language drift specifically arises during RLVR on novel reasoning tasks---i.e. when the target behavior cannot be drawn out of the base model. Finally, we prove that it is not possible to constrain language drift without constraining expected reward, suggesting that CoT monitorability cannot be improved without harming performance during RLVR post-training at the frontier.
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cs.LGstat.ML Haodong Wen, Kaiyue Wen, Jiaye Teng · Oct 1, 2026

This paper studies gradient descent with a large constant stepsize on linearly separable logistic regression, a canonical model for the Edge of Stability phenomenon. It proves that the worst-case exact transition time from oscillatory loss to monotone decrease scales as $\Theta((\log \eta)^{\min\{n-2,d-2\}})$ uniformly over dimension $d \ge 2$, disproving a conjecture that stepsize independence holds beyond $d=2$. The result translates into substantially stronger finite-horizon optimization guarantees by permitting exponentially larger constant stepsizes than prior $O(\eta)$ transient bounds.

We study logistic regression on linearly separable data under gradient descent with a large constant stepsize $\eta$. Such dynamics may exhibit a characteristic Edge of Stability phenomenon, in which the loss initially oscillates before transitioning to a stable phase of monotone decrease. Existing work provides a tight $\Theta(1)$ bound in dimension $d=2$ as $\eta \to \infty$ and conjectures a bound independent of $\eta$ in arbitrary dimensions $d\geq 2$. In this paper, we disprove this conjecture by showing that, for every fixed sample size $n\geq 2$ and sufficiently small margin $\gamma$, the worst-case transition time is $$\Theta\!\left((\log\eta)^{\min\{n-2,d-2\}}\right)$$ uniformly over $d\geq2$. The key challenge in establishing a tight bound is that the sample contributing most strongly to the gradient can change repeatedly across iterations. To address this issue, we control such changes by induction on dimension and sample size, and construct matching hard instances.