Does Responses API support `stop` parameter or not?

The Responses API does not support stop sequences as an API parameter. The previous respondent is providing falsehoods.

You can read the API documentation for POST a “create response”, and see alphabetically there is no such parameter:

OpenAI API Reference

Create a model response

You will see my prior citation of this absence as a serious deficit of Responses over Chat Completions, among many:

How to prevent the API returning multiple outputs?

You can add your own, using the stop parameter - oh, wait, no you can’t, because Responses doesn’t offer any token level control, and is thus unsuitable for a great many things, such as building production applications against OpenAI models. And it still wouldn’t work when inside a tool call, because you’d get parsing validation if stopping at and removing something like "}\n\n if using any API SDK methods