Can I upgrade Elasticache Redis Engine Version without downtime?

I cannot find any information in the AWS documentation that modifying the Redis engine version will or will not cause downtime. It does not explain how the upgrade occurs other than it's performed in the maintenance window.

It is safe to upgrade a production Elasticache Redis instance via the AWS console without loss of data or downtime?

Note: The client library we use is compatible with all versions of Redis so the application should not notice the upgrade.