source: pydantic/pydantic-ai#4138 (comment)
Initial Checks
Description
GenerateJsonSchema.typed_dict_schema() correctly uses extras_schema to produce typed additionalProperties when extra_behavior is set as a top-level field on the schema, but ignores it when extra_fields_behavior is set via the config dict — always producing additionalProperties: true instead of the typed schema.
This was partially addressed by #10785 / #12123, but only the top-level extra_behavior path was fixed. The config fallback path (the elif 'additionalProperties' not in json_schema branch at the bottom of typed_dict_schema) sets True without consulting extras_schema:
# pydantic/json_schema.py — GenerateJsonSchema.typed_dict_schema()
elif 'additionalProperties' not in json_schema:
extra = schema.get('config', {a}).get('extra_fields_behavior')
if extra == 'forbid':
json_schema['additionalProperties'] = False
elif extra == 'allow':
json_schema['additionalProperties'] = True # <-- ignores extras_schemaExample Code
from pydantic_core import core_schema
from pydantic.json_schema import GenerateJsonSchema
# Top-level extra_behavior — CORRECT
schema_top = core_schema.typed_dict_schema(
fields={'x': core_schema.typed_dict_field(core_schema.int_schema())},
extra_behavior='allow',
extras_schema=core_schema.int_schema(),
)
result_top = GenerateJsonSchema().generate(schema_top)
print(result_top['additionalProperties'])
# {'type': 'integer'} ✓
# Config extra_fields_behavior — BUG
schema_cfg = core_schema.typed_dict_schema(
fields={'x': core_schema.typed_dict_field(core_schema.int_schema())},
config=core_schema.CoreConfig(extra_fields_behavior='allow'),
extras_schema=core_schema.int_schema(),
)
result_cfg = GenerateJsonSchema().generate(schema_cfg)
print(result_cfg['additionalProperties'])
# True ✗ — should be {'type': 'integer'}Python, Pydantic & OS Version
pydantic version: 2.12.5
pydantic-core version: 2.33.2
python version: 3.13.3 (main, Apr 8 2025, 13:54:08) [Clang 16.0.0 (clang-1600.0.26.6)]
platform: macOS-15.5-arm64-arm-64bit-Mach-O
source: pydantic/pydantic-ai#4138 (comment)
Initial Checks
Description
GenerateJsonSchema.typed_dict_schema()correctly usesextras_schemato produce typedadditionalPropertieswhenextra_behavioris set as a top-level field on the schema, but ignores it whenextra_fields_behavioris set via the config dict — always producingadditionalProperties: trueinstead of the typed schema.This was partially addressed by #10785 / #12123, but only the top-level
extra_behaviorpath was fixed. Theconfigfallback path (theelif 'additionalProperties' not in json_schemabranch at the bottom oftyped_dict_schema) setsTruewithout consultingextras_schema:Example Code
Python, Pydantic & OS Version