SP-CACW: Convergence-Aware Client Weighting for Selfish Personalized Learning

Collaborative learning is sustainable only if it benefits each participant; yet, standard Federated Learning (FL) optimizes a global average that often fails to serve individual clients. In heterogeneous settings, a client may rationally prefer training alone rather than contributing to a global model that targets "average-case" optimality but under performs locally. In this work, we address the problem of Selfish Personalization (SP): How can a target client leverage peer data to minimize its own risk? While current techniques often rely on heuristic performance proxies or clustering that lack sharp theoretical support, we propose SP-Convergence-Aware Client Weighting (SP-CACW). This novel framework determines the contribution of peer clients by explicitly minimizing a theoretical convergence bound for the target. By doing so, our approach efficiently separates useful signal from imported bias on-the-fly during the training process. We provide convergence guarantees that establish the theoretical superiority of SP-CACW, alongside empirical results on the MNIST CIFAR datasets and LEAF Shakespeare.