Changelog

Versioning Policy

Socket.IO releases closely follow Semantic Versioning.

That means that with a version number x.y.z:

• when releasing critical bug fixes, we make a patch release by increasing the z number (ex: 1.2.3 to 1.2.4).
• when releasing new features or non-critical fixes, we make a minor release by increasing the y number (ex: 1.2.3 to 1.3.0).
• when releasing breaking changes, we make a major release by increasing the x number (ex: 1.2.3 to 2.0.0).

Breaking changes

Breaking changes are inconvenient for everyone, so we try to minimize the number of major releases.

We have had two major breaking changes impacting the Socket.IO protocol over the years:

• Socket.IO v2 was released in May 2017
• Socket.IO v3 was released in November 2020

info

Socket.IO v4 (released in March 2021) did not include any update to the Socket.IO protocol (only a couple of breaking changes in the Node.js server API), so it isn't counted here.

Reference: Migrating from 3.x to 4.0

Important milestones

Aside from the breaking changes listed above, here are the latest important changes in Socket.IO:

Version	Date	Description
4.7.0	June 2023	Support for WebTransport
4.6.0	February 2023	Introduction of Connection state recovery
4.4.0	November 2021	Support for uWebSockets.js
4.1.0	May 2021	Introduction of serverSideEmit()
4.0.0	March 2021	Rewrite to TypeScript

Version usage

As of June 2024:

socket.io package

socket.io-client package