Byzantine Eventual Consistency for Reliable Local-First Software

Slides from a keynote given at the 45th International Symposium on Reliable Distributed Systems (SRDS), Rome, Italy, 24 September 2026
https://srds-conference.org/
https://martin.kleppmann.com/2026/09/24/srds-keynote.html

Abstract:

Local-first software, a growing industry movement, aims to make collaborative applications (such as text and graphics editors, spreadsheets, etc.) resilient against server failure by making the client software on the end user’s device a full replica of the application state, and allowing it to sync with other replicas in a decentralised fashion. This has many advantages, but also introduces new challenges, since the system can no longer rely on a central server to maintain the consistency and security of the collaborative document, and practical systems have to tolerate potentially malicious clients. This talk gives an overview of our work on Byzantine Eventual Consistency, and how the open source Automerge library makes this approach efficient.

Transcript

2. Figma 2
39. 2.00472 https://arxiv.org /abs/201 PaPoC 2022
65. https://www.inkandswitch.com/keyhive/ 65
97. PaPoC 2026 97
107. References • Alex Good, John Mumm, and Brooklyn Zelenka. Keyhive lab notebook: Local-first access control. Ink & Switch, 2026. https://www.inkandswitch.com/keyhive/ • Kegan Dougal. ERA: Epoch-Resolved Arbitration for Duelling Admins in Group Management CRDTs. PaPoC 2026. doi:10.1145/3806077.3806691 • Martin Kleppmann. Making CRDTs Byzantine Fault Tolerant. PaPoC 2022. doi:10.1145/3517209.3524042 • Liangrun Da. Design and Verification of Byzantine Fault Tolerant CRDTs. Master’s Thesis, TU Munich, 2024. https://bit.ly/bft-crdt-isabelle • Martin Kleppmann and Heidi Howard. Byzantine Eventual Consistency and the Fundamental Limits of Peer-to-Peer Databases. Preprint, 2020. https://arxiv.org/abs/2012.00472 • Martin Kleppmann, Adam Wiggins, Peter van Hardenberg, and Mark McGranaghan. Local-first software: You own your data, in spite of the cloud. Onward! 2019. doi:10.1145/3359591.3359737