The Couchbase .NET SDK version 2.1.0 introduces the ability to override the default JSON serializer, NewtonSoft.NET, with a custom serializer by extending the ITypeSerializer interface. This update allows developers to implement faster JSON serializers like Jil, which offers performance enhancements by optimizing memory allocation and access. Implementing a custom serializer involves creating a new ITypeSerializer implementation and configuring the ClientConfiguration to use this serializer. Jil, based on the Sigil IL generation library, efficiently handles serialization tasks by employing strategies such as avoiding allocations and optimizing CPU operations. The process of setting up a custom serializer is straightforward, requiring adjustments to the ClientConfiguration or utilizing configuration files like Web.Config. The enhancement aims to provide flexibility and improve performance in serialization tasks within the Couchbase .NET environment.