Explanation

For App Engine, the correct feature to direct a small percentage of traffic (like 1%) to a new version is Traffic splitting by version. This is a built-in App Engine feature that allows you to split traffic between different versions of your application.

Why other options are incorrect:

• A) Canary deployment on GKE: This is for Google Kubernetes Engine deployments, not App Engine.
• C) Separate test project: While you could use a separate project for testing, this doesn't achieve the goal of having 1% of users see the new version in the same production environment.
• D) Cloud Run gradual rollout: This is specific to Cloud Run services, not App Engine.

How Traffic Splitting works in App Engine:

1. Deploy your new version to App Engine
2. Use the gcloud app services set-traffic command or the Cloud Console
3. Specify the traffic percentage for each version
4. For example: gcloud app services set-traffic default --splits v2=0.01,v1=0.99

This allows you to gradually roll out new versions to a small percentage of users for testing before making it available to everyone.