EquiTabPFN: A Target-Permutation Equivariant Prior Fitted Network

Michael Arbel (INRIA) · David Salinas (ELLIS Institue Tuebingen) · Frank Hutter (ELLIS Institute Tübingen & University of Freiburg)

bi-attention mechanismclassification benchmarks computational overhead empirical evaluationensembling strategiesequivariance gapequivariant decodersequivariant encodersfoundational models in-context learning model stability permutation invariance pre-training tabular datatarget-equivariance

Recent foundational models for tabular data, such as TabPFN, excel at adapting to new tasks via in-context learning but remain constrained to a fixed, pre-defined number of target dimensions—often necessitating costly ensembling strategies. We trace this constraint to a deeper architectural shortcoming: these models lack target-equivariance, so that permuting target-dimension orderings alters their predictions. This deficiency gives rise to an irreducible “equivariance gap,” an error term that introduces instability in predictions. We eliminate this gap by designing a fully target-equivariant architecture—ensuring permutation invariance via equivariant encoders, decoders, and a bi-attention mechanism. Empirical evaluation on standard classification benchmarks shows that, on datasets with more classes than those seen during pre-training, our model matches or surpasses existing methods while incurring lower computational overhead.