Can I see my Google Maps spend broken down by API key?

Yes. The Google Cloud Console billing reports page provides API key level grouping. In the Group by menu, choose goog-maps-api-key-suffix. The report presents spend by API key suffix.

Google Maps Metrics

In addition to the spend insight that billing reports provide, you can also inspect usage/traffic at the API key level.

1. In Cloud Console navigate to Google Maps > Metrics for your project.

2. Under Show Filters > Grouped by, choose Credential to present that graph.

Special Note on Client ID: You can recognize the usage associated with your Client ID with a credential identifier in the following format:

project_number: 12345678

References

How to calculate traffic by credential (API key)

What are best practices and patterns for managing usage and billing within Google Maps Platform?

How are Client IDs managed differently from API keys?