A few things that I thougth to add here, as I’ve seem them mentioned a few times in other posts:
Compatibility between different models in Responses API
At this moment, changing from a conversation that used a reasoning model will not allow a non reasoning model to continue it using previous_response_id.
It would make sense to allow it even if losing reasoning summaries, because it saves costs when only polishing some responses, like using gpt-4.1.mini just for formatting.
Here are some posts mentioning this problem:
- Switching model with Responses API breaks multi-shot context (previous model's responses not available for other models) - #13 by aprendendo.next
- Using previous_response_id fails when swapping from reasoning -> non-reasoning models
Issues with the list input items endpoint
It provides a way to retrieve a conversation, which theoretically allow us to recreate the inputs and build a workaround to the problem mentioned earlier.
But its response is not compatible with the input parameter and has may types of input data, which is doable but makes the conversation reconstruction very troublesome.
Here is a snapshot of possible responses it returns.
ResponseItem: TypeAlias = Annotated[
Union[
ResponseInputMessageItem,
ResponseOutputMessage,
ResponseFileSearchToolCall,
ResponseComputerToolCall,
ResponseComputerToolCallOutputItem,
ResponseFunctionWebSearch,
ResponseFunctionToolCallItem,
ResponseFunctionToolCallOutputItem,
ImageGenerationCall,
ResponseCodeInterpreterToolCall,
LocalShellCall,
LocalShellCallOutput,
McpListTools,
McpApprovalRequest,
McpApprovalResponse,
McpCall,
],
PropertyInfo(discriminator="type"),