arXiv:2611.08083v1 Announce Type: cross Abstract: Replicated data types providing strong eventual consistency offer a principled foundation for developing decentralized software. Yet existing approaches to programming such data types leave access control unresolved: they either provide none at all, delegate it to a trusted coordinator, reintroducing the centralization they were designed to avoid, or tie it to specific data-type constructions, while typically assuming non-Byzantine replicas and static policies. We present GUARDTs: Guarded Unforgeable Algebraic Replicated Data Types, which embed fine-grained permissions directly into the application data model, operate without a central authority, support dynamic policy evolution, and tolerate Byzantine replicas. We formally prove that GUARDTs guarantee confidentiality, integrity, and availability and show empirically that their access control adds negligible overhead on top of the cost of Byzantine-resilient replication itself.