Lifecycle guide for System.Collections.Immutable from Microsoft

All releases, patches, maintenance and support periods at a glance

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📅 Last update on 2026-09-07

What is System.Collections.Immutable?

Automate product release and end-of-life management

This package provides collections that are thread safe and guaranteed to never change their contents, also known as immutable collections. Like strings, any methods that perform modifications will not change the existing instance but instead return a new instance. For efficiency reasons, the implementation uses a sharing mechanism to ensure that newly created instances share as much data as possible with the previous instance while ensuring that operations have a predictable time complexity. The System.Collections.Immutable library is built-in as part of the shared framework in .NET Runtime. The package can be installed when you need to use it in other target frameworks.

The entire lifecycle of System.Collections.Immutable

The following figure shows you the visualised product life cycle of System.Collections.Immutable. You can see all releases with the latest patch version, the long-term support characteristics (orange flag in the green circle, the periods for version provision, maintenance and support.