ValidationError when using prefixItems in google.genai.types.Schema

[stri8ed]

Environment details

• Programming language: Python
• OS: Mac
• Language runtime version: 3.12
• Package version: 1.40.0

Steps to reproduce

1. Define a JSON schema that uses prefixItems.
2. Attempt to validate it using google.genai.types.Schema.model_validate().

import google.genai.types as types
import pydantic

JSON_SCHEMA = {
    "type": "array",
    "prefixItems": [
        {
          "type": "object",
          "properties": {
            "id": {"const": 42},
            "original": {"type": "string", "maxLength": 750},
            "thoughts": {"type": "string", "maxLength": 650},
            "translation": {"type": "string", "maxLength": 1000}
          }
        }
    ],
    "items": {
        "type": "object",
        "properties": {
            "id": {"type": "integer"},
            "original": {"type": "string"},
            "thoughts": {"type": "string"},
            "translation": {"type": "string"}
        },
        "required": ["id", "original", "thoughts", "translation"]
    }
}

try:
    schema = types.Schema.model_validate(JSON_SCHEMA)
except pydantic.ValidationError as e:
    print(f"ERROR: {e}")

Outputs:

ERROR: 1 validation error for Schema
prefixItems
  Extra inputs are not permitted [type=extra_forbidden, input_value=[{'type': 'object', 'prop...', 'maxLength': 1000}}}], input_type=list]
    For further information visit https://errors.pydantic.dev/2.11/v/extra_forbidden

As per this press release from May, prefixItems should be supported.

[sasha-gitg]

Try passing the json schema directly to response_json_schema,

ie client.models.generate_content(..., config={'response_json_schema': JSON_SCHEMA}

[stri8ed]

Try passing the json schema directly to response_json_schema,

ie client.models.generate_content(..., config={'response_json_schema': JSON_SCHEMA}

It results in the same error. I used the model_validate call just to simplify the reproduction. I believe the generate_content function calls model_validate before sending the request.

[sasha-gitg]

That's for response_schema, what exception is raised for response_json_schema?

[github-actions]

This issue has been marked as stale because it has been open for 7 days with no activity. It will be closed in 2 days if no further activity occurs.