Active In-Context Learning for Tabular Foundation Models

Wilailuck Treerath; Fabrizio Pittorino

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arXiv · 2603.27385

Active In-Context Learning for Tabular Foundation Models

Wilailuck Treerath·Fabrizio Pittorino

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Abstract

Active learning (AL) reduces labeling cost by querying informative samples, but in tabular settings its cold-start gains are often limited because uncertainty estimates are unreliable when models are trained on very few labels. Tabular foundation models such as TabPFN provide calibrated probabilistic predictions via in-context learning (ICL), i.e., without task-specific weight updates, enabling an AL regime in which the labeled context - rather than parameters - is iteratively optimized. We formalize Tabular Active In-Context Learning (Tab-AICL) and instantiate it with four acquisition rules: uncertainty (TabPFN-Margin), diversity (TabPFN-Coreset), an uncertainty-diversity hybrid (TabPFN-Hybrid), and a scalable two-stage method (TabPFN-Proxy-Hybrid) that shortlists candidates using a lightweight linear proxy before TabPFN-based selection. Across 20 classification benchmarks, Tab-AICL improves cold-start sample efficiency over retrained gradient-boosting baselines (CatBoost-Margin and XGBoost-Margin), measured by normalized AULC up to 100 labeled samples.

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Wilailuck Treerath, Fabrizio Pittorino. 2026-03-28. Active In-Context Learning for Tabular Foundation Models. https://arxiv.org/abs/2603.27385

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