What’s the difference between OCI Vault and OCI Key Management?

OCI Vault is the broader secrets management service (API keys, passwords, certificates); Key Management specifically refers to the encryption key lifecycle management capability within Vault used for encrypting data at rest.

Practical use

Use Vault secrets for application credentials and API keys; use Vault-managed keys (Key Management) when you need customer-managed encryption keys for services like Object Storage or Block Volume.