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Azure Functions runtime versions overview
Azure Functions supports multiple versions of the runtime. Learn the differences between them and how to choose the one that's right for you.
conceptual
devx-track-extended-java, devx-track-js, devx-track-python, ignite-2023, devx-track-ts
02/26/2024
programming-languages-set-functions

Azure Functions runtime versions overview

Azure Functions currently supports two versions of the runtime host. The following table details the currently supported runtime versions, their support level, and when they should be used:

Version Support level Description
4.x GA Recommended runtime version for functions in all languages. Check out Supported language versions.
1.x GA (support ends September 14, 2026) Supported only for C# apps that must use .NET Framework. This version is in maintenance mode, with enhancements provided only in later versions. Support will end for version 1.x on September 14, 2026. We highly recommend you migrate your apps to version 4.x, which supports .NET Framework 4.8, .NET 6, .NET 8, and .NET 9.

Important

As of December 13, 2022, function apps running on versions 2.x and 3.x of the Azure Functions runtime have reached the end of extended support. For more information, see Retired versions.

This article details some of the differences between supported versions, how you can create each version, and how to change the version on which your functions run.

Levels of support

[!INCLUDE functions-support-levels]

Languages

All functions in a function app must share the same language. You choose the language of functions in your function app when you create the app. The language of your function app is maintained in the FUNCTIONS_WORKER_RUNTIME setting, and can't be changed when there are existing functions.

[!INCLUDE functions-supported-languages]

For information about the language versions of previously supported versions of the Functions runtime, see Retired runtime versions.

Run on a specific version

The version of the Functions runtime used by published apps in Azure is dictated by the FUNCTIONS_EXTENSION_VERSION application setting. In some cases and for certain languages, other settings can apply.

By default, function apps created in the Azure portal, by the Azure CLI, or from Visual Studio tools are set to version 4.x. You can modify this version if needed. You can only downgrade the runtime version to 1.x after you create your function app but before you add any functions. Updating to a later major version is allowed even with apps that have existing functions.

Migrating existing function apps

[!INCLUDE functions-migrate-apps]

Changing version of apps in Azure

The following major runtime version values are used:

Value Runtime target
~4 4.x
~1 1.x

Important

Don't arbitrarily change this app setting, because other app setting changes and changes to your function code might be required. For existing function apps, follow the migration instructions.

Pinning to a specific minor version

To resolve issues your function app could have when running on the latest major version, you have to temporarily pin your app to a specific minor version. Pinning gives you time to get your app running correctly on the latest major version. The way that you pin to a minor version differs between Windows and Linux. To learn more, see How to target Azure Functions runtime versions.

Older minor versions are periodically removed from Functions. For the latest news about Azure Functions releases, including the removal of specific older minor versions, monitor Azure App Service announcements.

Minimum extension versions

::: zone pivot="programming-language-csharp" There's technically not a correlation between binding extension versions and the Functions runtime version. However, starting with version 4.x the Functions runtime enforces a minimum version for all trigger and binding extensions.

If you receive a warning about a package not meeting a minimum required version, you should update that NuGet package to the minimum version as you normally would. The minimum version requirements for extensions used in Functions v4.x can be found in the linked configuration file.

For C# script, update the extension bundle reference in the host.json as follows:

{
    "version": "2.0",
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[4.0.0, 5.0.0)"
    }
}

::: zone-end ::: zone pivot="programming-language-java,programming-language-javascript,programming-language-typescript,programming-language-powershell,programming-language-python" There's technically not a correlation between extension bundle versions and the Functions runtime version. However, starting with version 4.x the Functions runtime enforces a minimum version for extension bundles.

If you receive a warning about your extension bundle version not meeting a minimum required version, update your existing extension bundle reference in the host.json as follows:

{
    "version": "2.0",
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[4.0.0, 5.0.0)"
    }
}

To learn more about extension bundles, see Extension bundles. ::: zone-end

Retired versions

[!INCLUDE functions-runtime-1x-retirement-note]

These versions of the Functions runtime reached the end of extended support on December 13, 2022.

Version Current support level Previous support level
3.x Out-of-support GA
2.x Out-of-support GA

As soon as possible, you should migrate your apps to version 4.x to obtain full support. For a complete set of language-specific migration instructions, see Migrate apps to Azure Functions version 4.x.

Apps using versions 2.x and 3.x can still be created and deployed from your CI/CD DevOps pipeline, and all existing apps continue to run without breaking changes. However, your apps aren't eligible for new features, security patches, and performance optimizations. You can only get related service support after you upgrade your apps to version 4.x.

End of support for versions 2.x and 3.x is due to the end of support for .NET Core 3.1, which they had as a core dependency. This requirement affects all languages supported by Azure Functions.

Locally developed application versions

You can make the following updates to function apps to locally change the targeted versions.

Visual Studio runtime versions

In Visual Studio, you select the runtime version when you create a project. Azure Functions tools for Visual Studio supports the two major runtime versions. The correct version is used when debugging and publishing based on project settings. The version settings are defined in the .csproj file in the following properties:

Version 4.x

<TargetFramework>net8.0</TargetFramework>
<AzureFunctionsVersion>v4</AzureFunctionsVersion>

If you are using the isolated worker model, you can choose, net8.0, net6.0, or net48 as the target framework. You can also choose to use preview support for net9.0. If you are using the in-process model, you can choose net8.0 or net6.0, and you must include the Microsoft.NET.Sdk.Functions extension set to at least 4.4.0.

.NET 7 was previously supported on the isolated worker model but reached the end of official support on May 14, 2024.

Version 1.x

<TargetFramework>net48</TargetFramework>
<AzureFunctionsVersion>v1</AzureFunctionsVersion>

Visual Studio Code and Azure Functions Core Tools

Azure Functions Core Tools is used for command-line development and also by the Azure Functions extension for Visual Studio Code. For more information, see Install the Azure Functions Core Tools.

For Visual Studio Code development, you could also need to update the user setting for the azureFunctions.projectRuntime to match the version of the tools installed. This setting also updates the templates and languages used during function app creation.

Bindings

Starting with version 2.x, the runtime uses a new binding extensibility model that offers these advantages:

  • Support for third-party binding extensions.

  • Decoupling of runtime and bindings. This change allows binding extensions to be versioned and released independently. You can, for example, opt to upgrade to a version of an extension that relies on a newer version of an underlying SDK.

  • A lighter execution environment, where only the bindings in use are known and loaded by the runtime.

Except for HTTP and timer triggers, all bindings must be explicitly added to the function app project, or registered in the portal. For more information, see Register binding extensions.

The following table shows which bindings are supported in each runtime version.

[!INCLUDE Full bindings table]

[!INCLUDE Timeout Duration section]

Next steps

For more information, see the following resources: