How well the system handles more load by adding resources. Horizontal scaling adds more instances; vertical scaling makes one instance bigger.
You have done this if
You moved the API to stateless containers behind a load balancer so you could add replicas during a launch.
Say it in a review
The web and API tiers scale horizontally; the model side scales through provider quotas, which is the real ceiling.
On the AI Application map Web App, API Gateway, Model