Flex is not available for this model. for gpt-5.1-chat-latest

API
1

Trying to use service_tier=’flex’ for gpt-5.1 model, it works with

gpt-5.1 but not with gpt-5.1-chat-latest.

Getting error:

BadRequestError: Error code: 400 - {'error': {'message': 'Flex is not available for this model.', 'type': 'invalid_request_error', 'param': None, 'code': None}}

2

Hi and welcome to the community!

This is expected because all gpt-5 chat models are offered via standard processing only.