Subspace-Aware Feature Reshaping for Open-Set Graph Class-Incremental Learning

Graph class-incremental learning (GCIL) has emerged to address the challenge of learning from dynamically evolving graphs, which continuously learns new classes over a sequence of tasks while retaining performance on previously seen classes. However, existing GCIL methods assume a closed-set test distribution drawn only from seen tasks. This fundamentally contradicts real-world open-ended scenarios where future unknown classes inevitably emerge. Empirically, we observe that existing GCIL methods falter in such open-set settings due to severe representation drift and generalized overconfidence. To bridge this gap, we investigate the Open-Set GCIL problem and propose SAFER (Subspace-Aware FEature Reshaping), a novel framework that endows GCIL with intrinsic open-set capabilities under a replay-free constraint. Specifically, SAFER performs subspace-aware feature reshaping with drift-resilient fingerprints, unifying task routing and open-set rejection into a single energy-based metric. Furthermore, we introduce a geometric space-consistency regularization that explicitly improves intra-class compactness and suppresses cross-task representation drift. Extensive experiments on four benchmarks demonstrate that SAFER outperforms state-ofthe-art baselines by margins of up to 5.2% in accuracy and 31.3% in open-set AUROC, all while maintaining near-zero forgetting under strict noreplay constraints. The code has been released in https://github.com/ZhangWeichao0824/SAFER