GitHub adds BYOK and custom model usage fields to the Copilot usage metrics API

GitHub's Copilot usage metrics API now reports bring-your-own-key (BYOK) usage separately from Copilot-hosted model usage.

Local BYOK appears in the used_local_byok, totals_by_local_byok and active local BYOK user counts, and enterprise custom models are flagged with is_custom_enterprise_model in totals_by_client. Existing totals are unchanged.

The data is available to enterprise owners, enterprise billing managers, organization owners, and anyone with a custom organization or enterprise role that grants the View Copilot Metrics permission, and only when the Copilot usage metrics policy is enabled. GitHub's changelog says report days before the release do not include is_custom_enterprise_model, so the new flag has no history before the change.