null means undeclared and global is behaviorally identical: the credential follows the region OpenRouter records for the endpoint. europe or us lets requests to eu.openrouter.ai or us.openrouter.ai use this credential for that provider (private endpoints, endpoints pinned to another cloud region, cross-region inference profiles and video models are excluded). Self-declared and not verified by OpenRouter. For OpenAI and Fireworks the region comes from the key material (a {"api_key": ..., "region": ...} key), so the value must match the key’s region. Among other providers, only Azure accepts europe or us. Defaults to the key’s region for OpenAI and Fireworks, otherwise null.