pypi / pydantic-core

pydantic-core

What changed in pydantic-core 2, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-21.

72 breaking8 deprecations10 new APIs and options4 behavior and defaults16 fixes and other

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pydantic-core 2110 changes

Breaking changes 72

Fields annotated as Any no longer default to None and are required unless an explicit default is provided.
2.0.0upgrade guide
Url and Dsn types no longer inherit from str; convert them with str(url) when using APIs that expect a string.
2.0.0upgrade guide
Coercing int, float, and Decimal values to strings is optional and disabled by default.
2.0.0upgrade guide
Color Types have moved to the separately installable Pydantic Extra Types package.
2.0.0upgrade guide
This config setting has been removed.
2.0.0upgrade guide
Vanilla dataclasses no longer inherit the parent type's config; override config with the config parameter on the @dataclass decorator.
2.0.0upgrade guide
Pydantic dataclasses no longer support extra='allow'; extra='ignore' remains supported but does not store extra fields.
2.0.0upgrade guide
Dataclasses used as fields no longer accept tuples as validation inputs; use dictionaries instead.
2.0.0upgrade guide
Decimal is represented as a string in generated JSON schema and serialization.
2.0.0upgrade guide
This config setting has been removed.
2.0.0upgrade guide
Arbitrary keyword arguments are no longer added to JSON schema; pass extra schema data through json_schema_extra instead.
2.0.0upgrade guide
Use frozen instead.
2.0.0upgrade guide
The const property has been removed.
2.0.0upgrade guide
Constraints are no longer automatically pushed down to generic parameters; use typing.Annotated to annotate the parameter type.
2.0.0upgrade guide
Use the typing.Final type hint instead.
2.0.0upgrade guide
Use max_length instead.
2.0.0upgrade guide
Use min_length instead.
2.0.0upgrade guide
Use pattern instead.
2.0.0upgrade guide
Introduced as the replacement for validator, with new features; annotate generic container item types to validate their contents.
2.0.0upgrade guide
Validator functions no longer receive the config argument; access configuration through info.config instead.
2.0.0upgrade guide
Validator functions no longer receive the field argument; use info.field_name to look up the field in cls.model_fields.
2.0.0upgrade guide
Returns None when no alias is set, rather than returning the field name.
2.0.0upgrade guide
This config setting has been removed; use Annotated on fields to modify them.
2.0.0upgrade guide
Float values convert to integers only when their decimal part is zero, avoiding loss of fractional data.
2.0.0upgrade guide
Renamed from orm_mode.
2.0.0upgrade guide
Removed; generic BaseModel subclasses can now inherit from Generic directly.
2.0.0upgrade guide
Custom types should use __get_pydantic_core_schema__ in place of __get_validators__.
2.0.0upgrade guide
Custom JSON schema hooks use __get_pydantic_json_schema__ in place of __modify_schema__.
2.0.0upgrade guide
Removed because orm_mode and its implementation detail are no longer supported.
2.0.0upgrade guide
Removed along with orm_mode; it was an implementation detail of that feature.
2.0.0upgrade guide
Renamed from keep_untouched.
2.0.0upgrade guide
Validated generic collections are no longer guaranteed to preserve their input subtype; output types match the annotations, while BaseModel subclasses and dataclasses retain their types.
2.0.0upgrade guide
Iterables of pairs, including empty iterables, are no longer coerced to dictionaries during validation.
2.0.0upgrade guide
This config setting has been removed.
2.0.0upgrade guide
JSON serialization of non-string dictionary keys generally uses str(key), changing output for values such as None.
2.0.0upgrade guide
This config setting has been removed.
2.0.0upgrade guide
Renamed from schema_extra; also used to pass extra JSON schema data to Field.
2.0.0upgrade guide
Replaces construct() as the model construction method.
2.0.0upgrade guide
Replaces copy() as the model copying method.
2.0.0upgrade guide
Replaces dict() as the method for dumping model data.
2.0.0upgrade guide
Replaces json() for JSON serialization; output is compacted and may not exactly match json.dumps() output.
2.0.0upgrade guide
Models are equal only to BaseModel instances with matching type, field values, extra values, and private attribute values; they are no longer equal to dictionaries containing their data.
2.0.0upgrade guide
Replaces __fields__ as the name for model fields.
2.0.0upgrade guide
Replaces json_schema() as the model JSON schema method.
2.0.0upgrade guide
Replaces update_forward_refs() as the model rebuilding method.
2.0.0upgrade guide
Provides the JSON-loading behavior that previously came from parse_raw.
2.0.0upgrade guide
Generated JSON schema no longer preserves namedtuples as namedtuples.
2.0.0upgrade guide
An Optional-annotated field without a default is required but accepts None; Optional no longer implies a default of None.
2.0.0upgrade guide
The parse_env_var classmethod has been removed; customize settings sources to provide a parsing function.
2.0.0upgrade guide
Payment Card Numbers have moved to the separately installable Pydantic Extra Types package.
2.0.0upgrade guide
Renamed from allow_population_by_field_name.
2.0.0upgrade guide
Pydantic dataclass __post_init__ is now called after validation rather than before.
2.0.0upgrade guide
This config setting has been removed.
2.0.0upgrade guide
Removed because it became redundant after __post_init__ moved after validation.
2.0.0upgrade guide
Pydantic dataclasses no longer expose this attribute or use an underlying BaseModel; use TypeAdapter for related functionality.
2.0.0upgrade guide
Replaces __private_attributes__ as the name for private attributes.
2.0.0upgrade guide
Replaces __validators__ as the model validator attribute.
2.0.0upgrade guide
Deprecated in favor of model_validator; even when retained, skip_on_failure=False is no longer supported.
2.0.0upgrade guide
Replaces the __root__ field for defining a custom root model; RootModel types do not support arbitrary_types_allowed.
2.0.0upgrade guide
Removed; the default union_mode in Pydantic V2 is 'smart'.
2.0.0upgrade guide
Renamed from max_anystr_length.
2.0.0upgrade guide
Renamed from min_anystr_length.
2.0.0upgrade guide
Renamed from anystr_strip_whitespace.
2.0.0upgrade guide
Renamed from anystr_lower.
2.0.0upgrade guide
Renamed from anystr_upper.
2.0.0upgrade guide
Nested model serialization includes only fields defined on the annotated field type, rather than all fields from a subclass instance.
2.0.0upgrade guide
A TypeError raised in a validator is no longer converted into a ValidationError, preventing programming errors from being reported as validation failures.
2.0.0upgrade guide
Removed because Pydantic V2 behaves as though this setting were always True.
2.0.0upgrade guide
Set union_mode='left_to_right' on Field to restore the non-short-circuiting left-to-right union behavior.
2.0.0upgrade guide
URL validation appends a slash when a URL has no path, even if the input omitted the slash.
2.0.0upgrade guide
The decorator formerly named @validate_arguments is now @validate_call; attributes such as raw_function and validate are not preserved.
2.0.0upgrade guide
Renamed from validate_all and can be used to validate defaults, including as an alternative to validator always=True behavior.
2.0.0upgrade guide

Deprecations 8

Invalid *after* model validator function signatures now emit a deprecation warning instead of raising an error.
2.12.3release notes
The V1 pattern of defining a Config class in a BaseModel subclass is deprecated; use model_config instead.
2.0.0upgrade guide
Deprecated; model_validate can provide similar behavior when from_attributes=True is set in the model config.
2.0.0upgrade guide
Support for specifying json_encoders in model config is deprecated; serialization decorators are recommended for common custom serialization scenarios.
2.0.0upgrade guide
The notes advise against isinstance checks against parametrized generics; subclass the parametrized generic if such checks are needed.
2.0.0upgrade guide
Deprecated; load the data and pass it to model_validate.
2.0.0upgrade guide
Deprecated; use model_validate_json for JSON input or load the data before passing it to model_validate.
2.0.0upgrade guide
Deprecated in favor of field_validator; the each_item keyword is unavailable on field_validator, and validator signatures can no longer include field or config arguments.
2.0.0upgrade guide

New APIs and options 10

Adds a method to convert FieldInfo to a dictionary.
2.12.3release notes
Adds a decorator for customizing serialization.
2.0.0upgrade guide
Generic BaseModel subclasses can be declared by adding Generic as a parent class; mixing V1 and V2 models is not supported.
2.0.0upgrade guide
Choose whether generated JSON schema represents validation inputs or serialization outputs.
2.0.0upgrade guide
Specify model configuration with a class attribute dictionary; inherited configuration is merged across BaseModel parents, with later parents taking precedence for duplicate settings.
2.0.0upgrade guide
Replaces parse_obj() for validating model input and can be used in place of from_orm when from_attributes=True.
2.0.0upgrade guide
Introduced as the replacement for root_validator; under some circumstances it receives a model instance rather than a values dictionary.
2.0.0upgrade guide
JSON schema generation methods accept schema_generator so callers can provide a custom GenerateJsonSchema subclass.
2.0.0upgrade guide
Wrap dataclasses with TypeAdapter to validate, generate JSON schema, or access functionality previously requiring __pydantic_model__.
2.0.0upgrade guide
Use typing.Annotated to add custom validation or provide custom core-schema and JSON-schema functions without modifying the type itself.
2.0.0upgrade guide

Behavior and default changes 4

The allow_reuse keyword argument is no longer necessary; repeated-function detection now errors only for redefinition within a single class.
2.0.0upgrade guide
Generated JSON schema now targets draft 2020-12 by default, with some OpenAPI extensions.
2.0.0upgrade guide
Constructor arguments may be copied during validation and coercion, which matters when passing mutable objects.
2.0.0upgrade guide
Union validation preserves the input type when it matches a choice, even when that choice is not first in the union.
2.0.0upgrade guide

Fixes and other changes 16

Fix missing GC traversal on some struct fields and in GeneralFieldsSerializer.
2.13.5release notes
Validated model fields are counted once in smart unions.
2.13.5release notes
Validators can be reused when plugins are set.
2.13.5release notes
Preserve RootModel core metadata.
2.13.4release notes
Handle AttributeError subclasses when from_attributes is used.
2.13.3release notes
Fixes ValidationInfo.field_name being missing when using model_validate_json().
2.13.2release notes
Fixes ValidationInfo.data being missing when using model_validate_json().
2.13.1release notes
Fixes a pickle error when using model_construct() on a model with MISSING as a default value.
2.12.5release notes
Reverted URL credential percent-encoding in the build() method of AnyUrl and Dsn types.
2.12.4release notes
Validation no longer gets default values from defaultdict, fixing a regression in its validation behavior.
2.12.4release notes
Fields with exclude_if are excluded from JSON Schema required fields.
2.12.4release notes
Fixed serialization of IP address types to JSON when serialize_as_any is used by adding type inference.
2.12.4release notes
Fixed forward references in parent TypedDict classes on Python 3.14 and greater.
2.12.4release notes
Fixed field serializers on nested typed dictionaries.
2.12.4release notes
Mutations on FieldInfo classes reused as Annotated metadata are supported again, although this remains an unsupported pattern.
2.12.3release notes
Generated JSON schema for Optional fields now indicates that null is allowed.
2.0.0upgrade guide