The core and community extension repositories have backup servers (see duckdb-backup.org):

The backup servers serve byte-identical binaries, so signature checks are unaffected.

Automatic Fallback

Fallback is automatic: if the primary server is unreachable or returns a 5xx error, INSTALL retries the download from the backup server. No configuration is needed.

• A 4xx error (e.g., a non-existent extension) is reported directly, without contacting the backup server.
• The fallback only applies to the built-in core and community repositories. Repositories set via custom_extension_repository or INSTALL ... FROM '⟨url⟩' are used as-is.
• The installed extension's origin is still recorded as core or community.

Using the Backup Server Manually

To always install core extensions from the backup server, run:

SET custom_extension_repository = 'http://extensions.duckdb-backup.org';