Ory Kratos does not support using the same identifier (such as an email address) with multiple OIDC providers within a single project. The email address must be unique across all identities, regardless of the OIDC provider. If you attempt to sign in with a second OIDC provider using the same email, you will encounter an error indicating that the email is already used by another account, and the only option is to confirm with the original provider. This behavior cannot be circumvented or changed within a single Ory Kratos instance or project. The only potential workaround mentioned is to use multiple Ory Network projects or multiple Ory Kratos instances, but this approach is not documented or officially supported [kratos, login with different oidc providers, with same email address](https://github.com/ory/kratos/discussions/4162). If your use case requires the same email to be used with different OIDC providers without account linking or SSO, Ory's current design does not support this scenario.

Based on the available knowledge sources, there is no officially supported workaround within a single Ory Kratos project or instance to allow the same identifier (e.g., email address) to be used with multiple OIDC providers without triggering uniqueness errors. The official response from Ory is clear: the email address must be unique across all identities, regardless of provider. The only potential workaround mentioned is to use multiple Ory Network projects or multiple Ory Kratos instances, but this approach is not documented or officially supported, and no further details are provided on how to implement it [kratos, login with different oidc providers, with same email address](https://github.com/ory/kratos/discussions/4162). If this requirement is critical for your use case, you may need to consider architectural changes outside of Ory's documented and supported features.

Ory Kratos does not provide a built-in mechanism to deduplicate the subject (sub) across multiple OIDC providers during sign-in. The system treats each OIDC provider as a separate entity, and the uniqueness constraint is enforced on the identifier (such as email) across all providers. If two different OIDC providers return the same email or subject, Kratos will block the second sign-in attempt and prompt the user to confirm with the original provider. There is no supported way to automatically deduplicate or merge these identities during sign-in [kratos, login with different oidc providers, with same email address](https://github.com/ory/kratos/discussions/4162). The only workaround mentioned is to use separate Ory projects or instances, but this is not documented or officially supported. Therefore, if deduplication of subjects across providers is a strict requirement, Ory Kratos does not currently support this scenario out of the box, and the knowledge sources do not provide a recommended solution.