ClickOnce Automatic Updates Require Application Restart Despite Zero-Downtime Requirement

Answer

No. ClickOnce cannot apply an update to a running .NET 8 WinForms process without terminating and restarting it. True zero-downtime updates are not supported by the ClickOnce API.

Likely explanation

ClickOnce downloads the new deployment manifest and application files to a versioned cache, then the runtime must load the updated assemblies. Because the current process already holds references and file locks to the original assemblies, and ClickOnce does not use AssemblyLoadContext for in-process hot swapping, the only supported path is to end the current process and start a new one. Application.Restart() performs that termination.

Confirmed facts

• ApplicationDeployment.UpdateAsync downloads the update and then triggers Application.Restart().
• The restart happens before UpdateCompleted and CheckForUpdateCompleted events fire, so those events cannot cancel or defer it.
• There is no public property, event hook, or manifest setting to suppress the restart.
• AssemblyLoadContext supports unloading in custom scenarios, but ClickOnce-managed assemblies are not loaded into a swappable context for in-process replacement.

Steps for this case

1. Accept that the running process must exit; plan update windows or user prompts around the restart.
2. If zero-downtime is mandatory, move update logic out of ClickOnce: use a separate updater process or external orchestrator that launches the new version side by side and signals the old instance to shut down after draining work.
3. Keep the ClickOnce deployment pipeline for initial installation and patch delivery, but treat the update as a process replacement rather than an in-place patch.

Using a custom deployment manifest or non-standard ClickOnce host does not change the supported answer, though it may affect unsupported workarounds.