Create a separate API Gateway stage such as beta-v3 that is deployed from the new version and have developers use that stage's invoke URL is the correct option because it gives developers an isolated invoke URL and deployment that does not affect the production environment.

The beta stage provides a separate deployment lifecycle logging and configuration so the team can iterate on breaking changes while paying customers continue to use the stable production stage. Using a stage is operationally efficient because it reuses the same API configuration and authentication setup while providing a distinct URL and deployment target for testing.

Configure a canary release on the existing production stage and give developers a stage-variable URL to hit is unsuitable because canary routing splits live traffic on the same stage and could route some real customers to the breaking beta.

Issue new API keys in API Gateway and require developers to pass those keys to reach the new version is incorrect because API keys control identification quotas and usage plans and they do not determine which deployment or stage is invoked.

Build a brand-new API Gateway API for the new handlers and tell developers to call that new API would achieve isolation but it increases operational overhead for deployment authentication monitoring and lifecycle management compared with adding a stage.

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