From Zero to Hero: Advancing Zero-Shot Foundation Models for Tabular Outlier Detection

Outlier detection (OD) is widely used in practice; but its effective deployment on new tasks is hindered by lack of labeled outliers, which makes algorithm and hyperparameter selection notoriously hard. Foundation models (FMs) have transformed ML, and OD is no exception: Shen et al. (2025) introduced FOMO-0D, the first FM for OD, achieving remarkable performance against numerous baselines. This work introduces OUTFORMER, which advances FOMO-0D with (1) a mixture of synthetic priors and (2) self-evolving curriculum training. OUTFORMER is pretrained solely on synthetic labeled datasets and infers test labels of a new task by using its training data as in-context input. Inference is fast and zero-shot, requiring merely forward pass and no labeled outliers. Thanks to in-context learning, it requires zero additional work—no OD model training or bespoke model selection—enabling truly plug-and-play deployment. OUTFORMER achieves state-of-the-art performance on the prominent ADBench, as well as two new large-scale OD benchmarks that we introduce, comprising over 1,500 datasets, while maintaining speedy inference.

OUTFORMER is a plug-and-play foundation model for outlier detection. Instead of needing labeled outliers, model training, or hyperparameter tuning, it learns from synthetic datasets during pretraining and then detects outliers in a new dataset with a single forward pass. By using diverse synthetic priors and a self-evolving curriculum, it improves over FOMO-0D and achieves state-of-the-art results with low inference-time on ADBench and large-scale OD benchmarks.