Responses API with file input in the background mode: server error with PDFs

Adding data points and a workaround.

I’m hitting the same issue with gpt-5 (gpt-5-2025-08-07). After isolation testing, the bug is specifically background: true + input_file in message content. The same files work fine when routed through code interpreter’s container.file_ids with background mode on.

The dashboard shows “No input items” for failed runs, but the payload is confirmed correct (logged exact JSON before POST).

Failed request IDs: wfr_019d1db3689f76e18b535c7462f92b59 wfr_019d1e013b797b878cf46f648d6374e7 wfr_019d1e1cbc3a796e86336959cc91b6ab

Workaround: Route files through code interpreter container.file_ids instead of input_file. The model can still read the file — it just spins up a container.