Initial Checks

• I confirm that I'm using the latest version of Pydantic AI
• I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue

Description

See https://platform.openai.com/docs/guides/tools-web-search?api-mode=chat.

When using it with another model, we get this error:

pydantic_ai.exceptions.ModelHTTPError: status_code: 400, model_name: gpt-5, body: {'message': "Unknown parameter: 'web_search_options'.", 'type': 'invalid_request_error', 'param': 'web_search_options', 'code': 'unknown_parameter'}

We should use the model profile to proactively raise an error telling the user to use OpenAIResponsesModel instead if they're using the web search tool, unless they're using one of those specific models.

Example Code

from pydantic_ai import Agent, WebSearchTool

dinner_choosing_agent = Agent(
    model='openai:gpt-5',
    instructions="""Do what the user requests""",
    builtin_tools=[WebSearchTool()]
)
dinner_choosing_agent.run_sync('Help me find a thai restaurant near Mexico City')

Python, Pydantic AI & LLM client version

v1.0.1