Will Lewis

We will be decommissioning the sliding sync proxy next week (21/11/2024) and Element are removing client support in mid-January (17/01/2025).

Sliding Sync is designed to provide a significantly faster and more scalable sync experience in our clients. The initial implementation was first prototyped in Element Web backed by an entirely experimental server proxy. The implementation had half an eye on low bandwidth use cases, and the prototype led to MSC3575. We then realised that a simpler approach would be beneficial, and reused the same (experimental) proxy concept to facilitate beta testing with Element X, this time making it available on matrix.org. In doing so, we learned valuable lessons, leading to a refined and simplified API design in MSC4186. The proxy itself was only ever considered as a temporary arrangement to aid speed of development, rather than being a long term solution.

Simplified Sliding Sync MSC4186 (also known as native sliding sync), has since been implemented in Synapse, with encouraging results. Now that we don’t expect the API shape to change significantly, we recommend homeserver developers to implement MSC4186 natively.

The Matrix.org Foundation does not have the resources to keep up maintenance of the proxy service or its codebase, and plans to decommission the proxy from Mid-November and archive the sliding-sync repo.

Recognising that the community needs time to adopt sliding sync natively, Element will keep client support for the old API (MSC3575) until the 17th of January, 2025.

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