Differences between the isolated worker model and the in-process model for .NET on Azure Functions
There are two execution models for .NET functions:
| Execution model | Description |
|---|---|
| Isolated worker model | Your function code runs in a separate .NET worker process. Use with supported versions of .NET and .NET Framework. To learn more, see Develop .NET isolated worker process functions. |
| In-process model | Your function code runs in the same process as the Functions host process. Supports only Long Term Support (LTS) versions of .NET. To learn more, see Develop .NET class library functions. |
Important
Support will end for the in-process model on November 10, 2026. We highly recommend that you migrate your apps to the isolated worker model for full support.
This article describes the current state of the functional and behavioral differences between the two models. To migrate from the in-process model to the isolated worker model, see Migrate .NET apps from the in-process model to the isolated worker model.
Execution model comparison table
Use the following table to compare feature and functional differences between the two models:
| Feature/behavior | Isolated worker model | In-process model3 |
|---|---|---|
| Supported .NET versions | Long Term Support (LTS) versions, Standard Term Support (STS) versions, .NET Framework |
Long Term Support (LTS) versions, ending with .NET 8 |
| Core packages | Microsoft.Azure.Functions.Worker Microsoft.Azure.Functions.Worker.Sdk |
Microsoft.NET.Sdk.Functions |
| Binding extension packages | Microsoft.Azure.Functions.Worker.Extensions.* | Microsoft.Azure.WebJobs.Extensions.* |
| Durable Functions | Supported | Supported |
| Model types exposed by bindings | Simple types JSON serializable types Arrays/enumerations Service SDK types4 |
Simple types JSON serializable types Arrays/enumerations Service SDK types4 |
| HTTP trigger model types | HttpRequestData / HttpResponseData HttpRequest / IActionResult (using ASP.NET Core integration)5 |
HttpRequest / IActionResult5 HttpRequestMessage / HttpResponseMessage |
| Output binding interactions | Return values in an expanded model with: - single or multiple outputs - arrays of outputs |
Return values (single output only),out parameters,IAsyncCollector |
| Imperative bindings1 | Not supported - instead work with SDK types directly | Supported |
| Dependency injection | Supported (improved model consistent with .NET ecosystem) | Supported |
| Middleware | Supported | Not supported |
| Logging | ILogger<T>/ILogger obtained from FunctionContext or via dependency injection |
ILogger passed to the functionILogger<T> via dependency injection |
| Application Insights dependencies | Supported | Supported |
| Cancellation tokens | Supported | Supported |
| Cold start times2 | Configurable optimizations | Optimized |
| ReadyToRun | Supported | Supported |
| [Flex Consumption] | Supported | Not supported |
| .NET Aspire | Preview | Not supported |
1 When you need to interact with a service using parameters determined at runtime, using the corresponding service SDKs directly is recommended over using imperative bindings. The SDKs are less verbose, cover more scenarios, and have advantages for error handling and debugging purposes. This recommendation applies to both models.
2 Cold start times could be additionally impacted on Windows when using some preview versions of .NET due to just-in-time loading of preview frameworks. This impact applies to both the in-process and out-of-process models but can be noticeable when comparing across different versions. This delay for preview versions isn't present on Linux plans.
3 C# Script functions also run in-process and use the same libraries as in-process class library functions. For more information, see the Azure Functions C# script (.csx) developer reference.
4 Service SDK types include types from the Azure SDK for .NET such as BlobClient.
5 ASP.NET Core types are not supported for .NET Framework.
Supported versions
Versions of the Functions runtime support specific versions of .NET. To learn more about Functions versions, see Azure Functions runtime versions overview. Version support also depends on whether your functions run in-process or isolated worker process.
Note
To learn how to change the Functions runtime version used by your function app, see view and update the current runtime version.
The following table shows the highest level of .NET or .NET Framework that can be used with a specific version of Functions.
| Functions runtime version | Isolated worker model | In-process model4 |
|---|---|---|
| Functions 4.x1 | .NET 9.0 .NET 8.0 .NET Framework 4.82 |
.NET 8.0 |
| Functions 1.x3 | n/a | .NET Framework 4.8 |
1 .NET 6 was previously supported on both models but reached the end of official support on November 12, 2024. .NET 7 was previously supported on the isolated worker model but reached the end of official support on May 14, 2024.
2 The build process also requires the .NET SDK.
3 Support ends for version 1.x of the Azure Functions runtime on September 14, 2026. For more information, see this support announcement. For continued full support, you should migrate your apps to version 4.x.
4 Support ends for the in-process model on November 10, 2026. For more information, see this support announcement. For continued full support, you should migrate your apps to the isolated worker model.
For the latest news about Azure Functions releases, including the removal of specific older minor versions, monitor Azure App Service announcements.