Gson is a mature Java library for JSON serialization/deserialization, offering both streaming (JsonReader/JsonWriter) and tree-based (JsonElement hierarchy) APIs. It is centered around a flexible type adapter system (TypeAdapter/TypeAdapterFactory) that enables custom serialization for arbitrary Java objects, including support for Java generics, annotations (@SerializedName, @Expose, @JsonAdapter), and versioning. The core module provides reflection-based adapters for most common types, while extras and proto modules extend support for runtime polymorphism and Protocol Buffers. The library is in maintenance mode (bug fixes only, no major new features), but remains actively maintained with CI builds on multiple JDKs (11 through 25), integration tests for JPMS, GraalVM native image, and code shrinking (ProGuard/R8). Its design emphasizes extensibility and backward compatibility, though it relies heavily on Java reflection and sun.misc.Unsafe, which may pose risks on future JDK versions.