The problem

Reasoning models (o4-mini for example) throws the error "Error talking to OpenAI: Error code: 404"

What version of Home Assistant Core has the issue?

core-2025.8.0

What was the last working version of Home Assistant Core?

core-2025.7.4

What type of installation are you running?

Home Assistant OS

Integration causing the issue

OpenAI Conversation

Link to integration documentation on our website

https://www.home-assistant.io/integrations/openai_conversation

Diagnostics information

No response

Example YAML snippet

Anything in the logs that might be useful for us?

2025-08-08 09:15:00.517 ERROR (MainThread) [homeassistant.components.openai_conversation] Error talking to OpenAI: Error code: 404 - {'error': {'message': "Item with id 'rs_689595e2dab08192a81c945b6fb2fde2013adb5fa8460d9f' not found. Items are not persisted when `store` is set to false. Try again with `store` set to true, or remove this item from your input.", 'type': 'invalid_request_error', 'param': 'input', 'code': None}}

Additional information

No response