In-cloud replication
In-cloud replication is a COS configuration item for buckets. By setting in-cloud replication rules, you can automatically and asynchronously copy incremental objects in buckets across different regions. Once in-cloud replication is enabled, COS precisely copies the object content in the source bucket (such as the object metadata and version ID) to the destination bucket, and the copied object replicas have completely consistent attributes with the source objects. In addition, operations on objects in the source bucket, such as uploading or deleting objects, are also copied to the destination bucket.
The destination bucket should also use COS for object storage.

Cross-cloud replication
Cross-cloud replication is an advanced feature provided by COS that enables object migration between different clouds through cross-cloud replication rule configuration. This feature supports copying objects to any COS destination bucket that supports the S3 protocol, allowing object replication and migration as long as the network is smooth.
Cross-cloud replication can precisely copy object content in the source bucket, including the object metadata and version ID. The copied object replicas have completely consistent attributes with the source objects. Compared to in-cloud replication, cross-cloud replication provides more powerful capabilities with broader coverage, suitable for various scenario requirements.