NeurIPS 2026 Papers

Open-world semi-supervised learning aims to use limited labeled data from known classes to classify unlabeled samples that contain both known and novel classes. Most existing methods over-rely on known classes and tend to generalize incorrectly in complex open-world settings. This leads to degraded pseudo-label quality and the model is often overconfident in wrong predictions. To address this, this paper proposes a **M**itigating **C**onfidence **M**iscalibration Method in **Open**-World Semi-Supervised Learning (**OpenMCM**). By leveraging discriminative knowledge from known classes to guide learning in the novel class space, our method effectively mitigates overconfident misclassifications and improves discrimination accuracy. Furthermore, we propose an adaptive threshold calibration strategy to independently determine optimal decision boundary for each class. By integrating a high-reliable pseudo-label fusion mechanism, we enhance recognition stability for novel classes. Experiments on three benchmark datasets ($i.e.$, CIFAR-10, CIFAR-100, and ImageNet-100) show that our framework achieves performance improvements over existing state-of-the-art methods.

Model-based reinforcement learning (MBRL) promises high sample efficiency but is often crippled by compounding model errors: small prediction inaccuracies accumulate rapidly over multi-step rollouts, leading to biased policy optimization. We propose FTA, a trajectory-level generative framework using conditional flow matching (CFM) instead of step-wise dynamics. To avoid curved, energy-inefficient paths, we introduce an optimal transport regularizer grounded in the Benamou–Brenier formula. This regularizer minimizes kinetic energy while enforcing exact state displacement, yielding straight, low-energy trajectories with provable linear error propagation. Since a static generator fails in online RL due to (i) shifting data distributions and (ii) mismatch between training (historical) and desired (high-return) conditionals, we add periodic retraining from the replay buffer and a value-guided ODE sampler that biases generation toward high returns via the current Q-function. Theoretically, the regularizer drives the flow toward the Wasserstein-2 optimal transport map, and value-guided sampling reduces asymptotic Q-estimate bias. On MuJoCo benchmarks, FTA consistently outperforms strong MBRL and model-free baselines in sample efficiency and final performance, and generalizes across tasks. By mitigating compounding errors at the trajectory level and adapting to online shifts, FTA offers a robust, data-efficient alternative to traditional dynamics models.

When learning new concepts sequentially, Vision-Language Models (VLMs) face forgetting that degrades both previously acquired tasks and inherent zero-shot capabilities. This challenge is particularly pronounced in the Cross-domain Task-Agnostic Incremental Learning (X-TAIL) setting, where the absence of explicit task identifiers forces diverse concepts to coexist within a unified and crowded multi-modal space. In this context, we identify an underexplored vulnerability termed Asymmetric Boundary Encroachment (ABE). Even when historical feature spaces remain stable, unconstrained new text features actively encroach upon these established sub-spaces during training. To systematically counteract ABE, we propose a unified framework. First, we introduce Analytic Decision Boundary (ADB), which constructs a geometric defense by enforcing an analytic margin derived from cumulative statistics to secure historical multi-modal boundaries. Furthermore, we integrate Orthogonal Visual Adaptation (OVA) and Analytic Ridge Classifier (ARC) to safely evolve the visual backbone and enhance joint inference. Experiments under X-TAIL setting demonstrate that our framework effectively mitigates ABE and consistently achieves new state-of-the-art performance. Our code is available at https://anonymous.4open.science/r/abe-cl-vlm.

Instruction-guided image editing models are mostly trained and evaluated on executable requests, yet many real user instructions are non-operative for the given image. Reliable editing therefore requires reasoning not only about how to edit, but also whether to edit and what to ignore. We introduce \bench{}, a large-scale benchmark for non-operative image editing, with 1.1M instructions over 31K images across seven categories spanning symbolic, grounded, physical, and logical non-executability, plus a 35K-sample partial-edit test set evaluating selective execution when one clause is feasible and another is not. A 700-sample internal audit confirms a 94.9\% true no-op rate with $\kappa=0.87$. Evaluating 13 systems reveals a clear action--abstention dissociation: frontier editors achieve strong standard editing quality but still over-edit more than 40\% of no-op samples. Three complementary perceptual, feature-level, and vision-language metrics further surface distinct failure modes across architectures. As a reference baseline, JUDGE-THEN-EDIT BAGEL—a feasibility-aware BAGEL variant trained on a 150K mixture of full-edit, partial-edit, and no-op data—reduces over-edit rate from 41.7\% to 12.6\%. Our results show that abstention is a distinct capability that current benchmarks fail to measure.

Flow matching has emerged as a powerful alternative to diffusion models for generative modeling, but standard conditional flow matching is fundamentally misaligned with partially observed time series: starting from an uninformed Gaussian source forces the model to transport even already-observed entries from noise to the target, wasting capacity on trivially known regions. We propose MissPath-FM, a partial-observation-aware flow matching framework that redesigns the source prior and probability path for incomplete time series. MissPath-FM employs structured source priors (interpolation priors and Gaussian process posterior priors) to initialize the flow close to the observed signal, paired with a missingness-aware smooth path that allocates transport asymmetrically between observed and missing regions. We evaluate systematically across four datasets, four missingness mechanisms (MCAR, block, MNAR, irregular), two missing ratios, and three sequence lengths ($T \in \{24, 48, 96\}$), totaling 48 settings against eight baselines. MissPath-FM wins 29 of 32 settings at $T{=}48$ and 45 of 48 overall (93.8\%). Our ablations reveal a regime-dependent design hierarchy in which no single component suffices: under random missingness the source prior yields a large initial gain, but under structured block missingness it can fail entirely and the learned flow becomes indispensable; the missingness-aware path contributes a further $12\%$--$26\%$ across all regimes. Only the full pipeline achieves robust performance across all 48 settings. Mechanistically, structured priors shorten observed-region transport by up to $15\times$, concentrating the velocity field on genuinely uncertain entries.

In the animal kingdom, mirror self-recognition is a canonical probe of higher-order cognition, emerging only in some species. We ask whether an analogous functional capability emerges in embodied vision-language model (VLM) agents: can they recognize themselves in a mirror? We introduce a controlled 3D benchmark where a first-person VLM agent must infer a hidden body attribute from its reflection and select the matching target, while avoiding self–other misattribution. To separate mirror-grounded self-identification from shortcuts, we test mirror removal, misleading cues, and occluded reflections. We also evaluate the decision process through mirror seeking, temporal ordering, self-attribution, and reasoning–action consistency. Our experiments show that mirror-based self-identification emerges mainly in stronger VLMs. These models can use reflected evidence for action, whereas weaker models often inspect the mirror but fail to extract self-relevant information or misattribute their reflection. Language–vision conflict further shows that self-referential language alone is not evidence of grounded self-identification. Overall, mirror-based evaluation provides a diagnostic for whether embodied self-grounding is causally rooted in perception and action rather than priors, prompt compliance, or confabulation.

We provide theoretical guarantees for convergence of discrete-time policy mirror descent with inexact advantage functions updated using temporal difference (TD) learning for entropy regularised MDPs in Polish state and action spaces. We rigorously derive sufficient conditions under which the single-loop actor-critic scheme is stable and convergent. To weaken these conditions, we introduce a variant that performs multiple TD steps per policy update and derive an explicit lower bound on the number of TD steps required to ensure stability. Finally, we establish sub-linear convergence when the number of TD steps grows logarithmically with the number of policy updates, and linear convergence when it grows linearly under a concentrability assumption.

We study two variants of the mirror descent-ascent (MDA) algorithm for solving min-max problems on the space of measures: simultaneous and alternating. We work under assumptions of convexity-concavity and relative smoothness of the payoff function with respect to a suitable Bregman divergence, defined on the space of measures via flat derivatives. We establish non-asymptotic convergence rates to mixed Nash equilibria, measured in the Nikaido-Isoda error, proving an $\mathcal{O}(N^{-1/2})$ rate for simultaneous MDA and an improved $\mathcal{O}(N^{-2/3})$ rate for alternating MDA. The main technical contribution is an infinite-dimensional dual space analysis that relates Bregman divergences on measures to dual Bregman divergences on spaces of bounded continuous functions, allowing us to control asymmetric commutator terms created by alternating updates. The results substantially generalize prior analyses restricted to bilinear objectives and also apply to nonlinear convex-concave problems on measure spaces, thereby providing a unified theoretical foundation for MDA in mean-field min-max optimization.

Chain-of-Thought reasoning improves the explainability of large language models, yet verifying such reasoning remains difficult when intermediate steps express epistemic uncertainty rather than deterministic entailment. Neuro-symbolic verifiers typically translate reasoning steps into rigid first-order or SMT-style constraints. This forces each proposition into a binary truth regime and creates a Rigidity--Ambiguity Mismatch: uncertainty-marked claims such as may, likely, or suggests are either over-hardened into deterministic assertions or rejected as unverifiable. We propose ProbVeri, a probabilistic soft-logic framework for formal verification under uncertainty. The key idea is to represent uncertainty-marked reasoning steps as weighted soft logical constraints over continuous truth assignments, so that partial evidential support remains expressible. Building on this soft-logic representation, we formulate verification as a contrastive energy minimization problem: a step is considered supported when its natural interpretation has lower verification energy than its negated counterpart under the same evidence, soft rules, and assumption regularization. Probabilistic Soft Logic defines the logical energy through weighted hinge-loss constraints. We introduce a support-grounded assumption penalty that discourages unsupported latent bridge assumptions between context and claim. The resulting energy gap provides a confidence-scored verification signal that separates unsupported steps from weakly but consistently supported inferences. Experiments on ProofWriter, BioASQ, and LegalBench-SARA show that ProbVeri recovers more verified-correct reasoning traces than rigid verifiers while reducing over-acceptance compared with soft-only PSL. These results suggest that uncertainty-aware verification benefits from soft logical formalization and contrastive comparison between natural and negated interpretations.

Speech large language models (SLMs) are typically built from text large language model (TLM) checkpoints, yet they still suffer from a substantial modality gap. Prior work has mainly attempted to reduce this gap from the output side by making speech generation more text-like, but the gap remains. We argue that the key remaining bottleneck lies on the input side. We propose TextPro-SLM, an SLM that makes spoken input more closely resemble that of a prosody-aware text LLM. TextPro-SLM combines WhisperPro, a unified speech encoder that produces synchronized text tokens and prosody embeddings, with an LLM backbone trained to preserve the semantic capabilities of the original TLM while learning paralinguistic understanding. Experiments show that TextPro-SLM achieves the lowest modality gap among leading SLMs at both 3B and 7B scales, while also delivering strong overall performance on paralinguistic understanding tasks. These gains are achieved with only roughly 1,000 hours of audio training data, suggesting that reducing the modality gap from the input side is both effective and data-efficient.

Tree ensembles such as random forests (RFs) and gradient boosting machines (GBMs) are among the most widely used supervised learners, yet their theoretical properties remain incompletely understood. We adopt a spectral perspective on these algorithms, with two main contributions. First, we derive minimax-optimal convergence for RF regression, showing that, under mild regularity conditions on tree growth, the eigenvalue decay of the induced kernel operator governs the statistical rate. Second, we exploit this spectral viewpoint to develop compression schemes for tree ensembles. For RFs, leading eigenfunctions of the kernel operator capture the dominant predictive directions; for GBMs, leading singular vectors of the smoother matrix play an analogous role. Learning nonlinear maps for these spectral representations yields distilled models that are orders of magnitude smaller than the originals while maintaining competitive predictive performance. Our methods compare favorably to state of the art algorithms for forest pruning and rule extraction, with applications to resource constrained computing.

Using neural networks to learn optimal transport (OT) maps via minimax optimization has gained increasing interest in generative modeling. However, the widely used semi-dual OT maximin formulation is known to suffer from spurious global solutions that do not correspond to valid transport maps, often addressed by regularizing the objective function. We provide an alternative explanation by showing that these spurious solutions are not stationary points of the associated loss, implying that their appearance in practice stems from the optimizer's failure to converge to stationary points in nonconvex-nonconcave settings. However, when the $c$-concavity constraints are imposed on the potential, commonly to stabilize training, we show that these spurious solutions become stationary. Based on these observations, we propose solving the semi-dual OT problem without $c$-concavity constraints, using optimizers that can reliably converge to stationary points corresponding to OT maps in nonconvex-nonconcave settings, such as a two-timescale extragradient (TTS-EG) method. At the formulation level, we further show that a Lagrangian-based OT minimax formulation provably eliminates spurious global solutions. Our empirical results demonstrate that TTS-EG reliably recovers OT maps under both semi-dual and Lagrangian-based OT formulations without any regularization.

In overparameterised classification, training data can be linearly separable even when the underlying distribution is not. In this setting, gradient descent (GD) on the logistic loss diverges in norm while converging in direction to a max-margin interpolating classifier, whose implicit bias can be statistically suboptimal. In this work, we show that early stopping can overcome this suboptimality: in a Gaussian mixture model with label-flipping noise, GD stopped at an appropriate oracle time achieves minimax-optimal excess zero-one risk for covariance spectra with fast and continuous decay, including polynomial and exponential spectral decays. Our analysis combines a sharp upper bound for the early-stopped iterate with a matching statistical lower bound over arbitrary classifiers, yielding optimal rates that are validated by experiments. A central technical contribution is a new calibration result that converts excess logistic risk into excess zero-one risk; it handles the model misspecification induced by the label-flipping noise, and removes the square-root rate in standard bounds. We also establish a lower bound for linear interpolators, showing that interpolation can require exponentially more samples than early stopping to achieve the same excess risk.

Test-time alignment aims to adapt large language models (LLMs) to runtime objectives without updating their parameters. This is especially useful when the reward signal is user-specific, time-varying, or available only through a black-box evaluator. We propose a minimally invasive pre-logit steering method that optimizes additive interventions to the hidden states of a frozen LLM in order to improve reward while preserving the base model's behavior. Rather than penalizing the Euclidean norm of the steering vector, we derive an effort penalty from the local KL geometry of the induced token distribution. Specifically, we show that the per-token KL divergence between the steered and reference policies admits a second-order expansion given by a Fisher-quadratic form in the steering vector. This regularizer has an analytic gradient computable through matrix-vector products with the frozen language-model head, making it as inexpensive as a standard quadratic penalty while retaining a principled KL interpretation. We further decompose the sequence-level KL gradient into an analytic Fisher component and a trajectory-dependent score-function component, and introduce a hierarchy of Fisher surrogates with provable first-order equivalence in the small-steering regime. The resulting algorithm provides a training-free, reward-driven test-time alignment procedure that improves reward while controlling deviation from the base policy.

Retrieval-augmented and agentic workloads repeatedly prefill recurring predictable structured inputs (which we call 'spans') such as documents and code files. Yet, prefix caching in engines such as vLLM cannot reuse their KV entries unless they share identical prefixes with another request, while Position-Independent Caching (PIC) implementations within production-grade inference servers typically either require substantial server code changes or keep KV state outside the server, incurring host-to-device transfer overhead. We present Minimalistic PIC (MiniPIC): a minimal, flexible and fast vLLM design built from two ingredients: positional-encoding-free KV cache and user-controlled cache-reuse primitives. MiniPIC stores unrotated K vectors in the KV cache, applies RoPE to K tiles inside attention using per-request logical positions, and exposes three user-facing and token-level primitives: block-aligned padding, \ssep{}, and \pdep{}, that modify hashing behavior and effective block-level causal attention structure. With fewer than 100 lines of core-engine changes plus a custom attention backend, these primitives are sufficient to realize multiple PIC methods, including Block-Attention, EPIC, and Prompt Cache, within the same running vLLM instance, while natively integrating with KV cache CPU offload implementations. On 2WikiMultihopQA, MiniPIC with interleaved scheduling improves prefill throughput by 49\% over baseline vLLM, reduces cached-span time-to-first-token by up to two orders of magnitude, preserves the linear prefill scaling of uncached spans, and incurs only 5.7\% worst-case overhead.

We present the first mini-batch kernel $k$-means algorithm, offering an order of magnitude improvement in running time compared to the full batch algorithm. A single iteration of our algorithm takes $\widetilde{O}(kb^2)$ time, significantly faster than the $O(n^2)$ time required by the full batch kernel $k$-means, where $n$ is the dataset size and $b$ is the batch size. Extensive experiments demonstrate that our algorithm consistently achieves a 10-100x speedup with minimal loss in quality, addressing the slow runtime that has limited kernel $k$-means adoption in practice. We further complement these results with a theoretical analysis under an early stopping condition, proving that with a batch size of $\widetilde{\Omega}(\max \set{\gamma^{4}, \gamma^{2}}\cdot k\epsilon^{-2} )$, the algorithm terminates in $O(\gamma^2/\epsilon)$ iterations with high probability, where $\gamma$ bounds the norm of points in feature space and $\epsilon$ is a termination threshold. Our analysis holds for any reasonable center initialization, and when using $k$-means++ initialization, the algorithm achieves an approximation ratio of $O(\log k)$ in expectation. For normalized kernels, such as Gaussian or Laplacian it holds that $\gamma=1$. Taking $\epsilon = O(1)$ and $b=\Theta(k\log n)$, the algorithm terminates in $O(1)$ iterations, with each iteration running in $\widetilde{O}(k^3)$ time.

Despite rapid progress in artificial intelligence, current systems struggle with the interconnected challenges that define real-world decision making. Practical domains such as business management require open-ended optimization, actively learning environment dynamics from sparse experience, planning over long horizons in stochastic settings, and reasoning over spatial information. Yet no existing human-AI benchmarks assess how well agents integrate these challenges in a grounded decision-making context. To this end, we introduce Mini Amusement Parks (MAPs), an amusement-park simulator designed to evaluate an agent’s ability to model its environment, anticipate long-term consequences under uncertainty, and strategically operate a complex business. We provide expert human performance and a comprehensive evaluation of state-of-the-art agents, finding experts outperform these systems by 11.4× on easy mode and 15.3× on medium mode. Our analysis reveals persistent weaknesses in long-horizon planning, sample-efficient learning, spatial reasoning, and modelling uncertainty. By unifying these challenges within a single environment, MAPs offers a new foundation for benchmarking agents capable of adaptable decision making.

Long-horizon embodied intelligence requires agents to improve through interaction, not merely to execute plans generated from static goals. A central challenge is therefore to transform past executions into knowledge that can shape future decisions. Minecraft provides a representative testbed for this problem, where tasks such as crafting tools, building redstone components, and obtaining diamond equipment involve long prerequisite chains and are frequently disrupted by missing tools, blocked paths, GUI failures, or stagnant execution. To this end, we propose \textbf{MineEvolve}, a knowledge-driven self-evolution framework that converts execution feedback into actionable behavioral knowledge. MineEvolve first uses \underline{\emph{\textbf{\ding{182}Monitor}}} to convert each subgoal execution into typed feedback, including state changes, inventory changes, failure types, progress signals, and stagnation indicators. \underline{\emph{\textbf{\ding{183}Inducer}}} then derives reusable skills from successful executions and remedies from failed or stagnant executions. \underline{\emph{\textbf{\ding{184}Curator}}} validates, merges, filters, and retrieves these knowledge entries, while \underline{\emph{\textbf{\ding{185}Adaptor}}} uses them to repair the unfinished part of the plan under repeated failures or stagnation. Experiments on the Minecraft MCU long-horizon task suite show that MineEvolve consistently improves performance across multiple language-model planners, with larger gains on high-dependency task groups. Ablation and knowledge-accumulation studies further demonstrate that converting execution signals into structured behavioral knowledge is an effective path toward self-evolving embodied agents in long-horizon environments. Our code is available at \url{https://anonymous.4open.science/r/MineEvolve-1B5B}.

Recent advances in neural decoding have enabled the reconstruction of 3D visual content from functional magnetic resonance imaging (fMRI) signals, opening a route toward brain-conditioned 3D generation. Nevertheless, existing approaches largely rely on semantic or multi-view priors without explicitly modeling 3D geometric constraints, often leading to structural distortions and degraded geometric fidelity. To address this limitation, we propose MindShape, a geometry-aware neural decoding framework for fMRI-conditioned 3D reconstruction. Unlike previous methods, MindShape decodes superquadric geometry as an explicit, low-dimensional structural constraint and jointly conditions the 3D generation process on both geometric primitives and semantic descriptions, enabling semantically consistent and geometrically faithful reconstructions. Experiments show that MindShape improves reconstruction quality in terms of geometric consistency and semantic fidelity over existing baselines. These results suggest that explicit geometric primitives provide an effective structured interface between noisy neural measurements and controllable 3D generation.