Sourced from org.jetbrains.kotlinx:kotlinx-serialization-json's releases.

1.10.0

This release is based on Kotlin 2.3.0 and contains all of the changes from 1.10.0-RC. The only additional change is a fix for ProtoBuf packing of Kotlin unsigned types (#3079). Big thanks to KosmX for contributing the fix.

For your convenience, the changelog for 1.10.0-RC is duplicated below:

Stabilization of APIs

kotlinx-serialization 1.10 and subsequent releases will be focused on stabilization of existing APIs. The following APIs and configuration options are no longer experimental because they're widely used without any known major issues:

• Json configuration options: decodeEnumsCaseInsensitive, allowTrailingComma, allowComments, and prettyPrintIndent. (#3100)
• @EncodeDefault annotation and its modes. (#3106)
• JsonUnquotedLiteral constructor function (#2900)
• JsonPrimitive constructor function overloads that accept unsigned types. (#3117)
• JSON DSL functions on JsonElement with Nothing? overloads. (#3117)

Readiness for return value checker

Kotlin 2.3.0 introduces a new feature aimed at helping you to catch bugs related to the accidentally ignored return value of the function. kotlinx-serialization 1.10.0-RC code is fully marked for this feature, meaning that you can get warnings for unused function calls like Json.encodeToString(...). To get the warnings, the feature has to be enabled in your project as described here.

Polymorphism improvements

Polymorphic serialization received a couple of improvements in this release:

New subclassesOfSealed utility to automatically register sealed subclasses serializers in polymorphic modules (#2201).

Use it in your SerializersModule when configuring a polymorphic hierarchy which contains both abstract and sealed classes. For example, when root of your hierarchy is an interface, but most of your inheritors are sealed classes. The new function will register all known sealed subclasses for you, so you don’t need to list them one by one. This makes writing your SerializerModules much faster and simpler. Big thanks to Paul de Vrieze for contributing this feature.

Class discriminator conflict check rework (#3105).

If a payload already contains a property with the same name as the configured discriminator (for example, type), it is called a class discriminator conflict. To produce a correct output and allow more inputs to be deserialized at the same time, the following changes were made:

• Conflicts introduced by JsonNamingStrategy transformations are now detected during serialization as well and will cause SerializationException. It also affects non-polymorphic classes.
• Conflicts from ClassDisciminatorMode.ALL_JSON_OBJECTS and SerializersModuleBuilder.polymorphicDefaultSerializer are also detected.
• It is allowed to deserialize such a conflicting key for both sealed and open polymorphic hierarchies. Previously, it was possible in the sealed hierarchies alone due to missing assertion. See #1664 for details.

General improvements

• Add .serialName to MissingFieldException for clearer diagnostics. (#3114)
• Generate unique Automatic-Module-Name entries for metadata JARs. (#3109)
• Revised ProGuard rules and added R8 tests. (#3041)
• CBOR: Improved error message when a byte string/array type mismatch is encountered. (#3052)

Bugfixes

... (truncated)

Sourced from org.jetbrains.kotlinx:kotlinx-serialization-json's changelog.

1.10.0 / 2026-01-21

This release is based on Kotlin 2.3.0 and contains all of the changes from 1.10.0-RC. The only additional change is a fix for ProtoBuf packing of Kotlin unsigned types (#3079). Big thanks to KosmX for contributing the fix.

For your convenience, the changelog for 1.10.0-RC is duplicated below:

Stabilization of APIs

kotlinx-serialization 1.10 and subsequent releases will be focused on stabilization of existing APIs. The following APIs and configuration options are no longer experimental because they're widely used without any known major issues:

• Json configuration options: decodeEnumsCaseInsensitive, allowTrailingComma, allowComments, and prettyPrintIndent. (#3100)
• @EncodeDefault annotation and its modes. (#3106)
• JsonUnquotedLiteral constructor function (#2900)
• JsonPrimitive constructor function overloads that accept unsigned types. (#3117)
• JSON DSL functions on JsonElement with Nothing? overloads. (#3117)

Readiness for return value checker

Kotlin 2.3.0 introduces a new feature aimed at helping you to catch bugs related to the accidentally ignored return value of the function. kotlinx-serialization 1.10.0-RC code is fully marked for this feature, meaning that you can get warnings for unused function calls like Json.encodeToString(...). To get the warnings, the feature has to be enabled in your project as described here.

Polymorphism improvements

Polymorphic serialization received a couple of improvements in this release:

New subclassesOfSealed utility to automatically register sealed subclasses serializers in polymorphic modules (#2201). Use it in your SerializersModule when configuring a polymorphic hierarchy which contains both abstract and sealed classes. For example, when root of your hierarchy is an interface, but most of your inheritors are sealed classes. The new function will register all known sealed subclasses for you, so you don’t need to list them one by one. This makes writing your SerializerModules much faster and simpler. Big thanks to Paul de Vrieze for contributing this feature.

Class discriminator conflict check rework (#3105). If a payload already contains a property with the same name as the configured discriminator (for example, type), it is called a class discriminator conflict. To produce a correct output and allow more inputs to be deserialized at the same time, the following changes were made:

• Conflicts introduced by JsonNamingStrategy transformations are now detected during serialization as well and will cause SerializationException. It also affects non-polymorphic classes.
• Conflicts from ClassDisciminatorMode.ALL_JSON_OBJECTS and SerializersModuleBuilder.polymorphicDefaultSerializer are also detected.
• It is allowed to deserialize such a conflicting key for both sealed and open polymorphic hierarchies. Previously, it was possible in the sealed hierarchies alone due to missing assertion. See #1664 for details.

General improvements

... (truncated)

• 370c4e3 Prepare 1.10.0 release (#3142)
• eaa4b0b Merge remote-tracking branch 'origin/master' into dev
• 0311f16 Fix ProtoBuf packing for kotlin unsigned types (#3079)
• a19df8c Add a disclaimer to "Other community-supported formats" section and slightly ...
• 2f8a874 Add JSON5 to community-supported formats (#3134)
• 975af2c Actualize releasing process document
• e8be81f Prepare 1.10.0-RC release
• e334d1c [CBOR] Fix various bugs in the decoder implementation
• d7ca108 Merge remote-tracking branch 'origin/master' into dev
• a5a3c97 IR inliner: Enable intra-module mode for kotlinx.serialization (#3128)
• Additional commits viewable in compare view

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