Metadata sizes for data objects in cloud storage systems can be reduced. For example, a computing system can receive, at a client device of a cloud storage system, a first object identifier associated with a data object in the cloud storage system. The computing system can use a reduction function to generate a second object identifier associated with the data object. The second object identifier can have a smaller byte size than the first object identifier. The computing system can transmit, to a server of the cloud storage system, the second object identifier to be stored in metadata associated with the data object in the cloud storage system.