The interactions interface is incompatible with the Vertex AI Express mode

The interactions (NextGen) interface is incompatible with the Vertex AI Express mode (API Key authentication).

When using Express mode, the client initializer enforces a mutual exclusion between the API key and the project/location parameters. Because the project and location are missing, the SDK fails to construct the required Vertex AI resource path (/v1beta1/projects/{project}/locations/{location}/interactions). Instead, it falls back to a default path (/v1beta1/interactions) on the Gemini Developer API server, which does not exist and results in a 404 Not Found error.

To use the interactions interface, you must use the standard GCP Credentials authentication mode by providing a project, location, and valid Google Cloud credentials.

Reproduce the interactions interface with Vertex AI Express mode and API-key authentication, then inspect the client initializer and resource-path construction described in the report. Done means the Express-mode configuration reaches the required project/location-based Vertex AI interactions path instead of the default Gemini Developer API path that returns 404.

Written by the indexing model from the issue text.