@misc{Armstrong2026ib,
  author = {Armstrong, Joss},
  title = {Source-Side Sufficiency for the Information Bottleneck: Exact Reduction and Finite-Block Equivalence},
  year = {2026},
  eprint = {2604.26744},
  archivePrefix = {arXiv},
  primaryClass = {cs.IT},
  doi = {10.48550/arXiv.2604.26744},
  url = {https://arxiv.org/abs/2604.26744},
  note = {Version 2, revised 2026-08-03}
}