Hey, thanks for confirming. Yep, it’s the same bug, and it affects all Composer versions 1, 1.5, 2, and 2.5.
About Auto, it’s not Composer 2.5. Auto is a separate routing layer that picks a model for the task on its own, and it ignores BYOK keys in settings. That’s why it doesn’t crash when an OpenAI API key is enabled. Named Composer models don’t have that ignore logic yet, so you get the error. You can use Auto as a workaround, but it’s not exactly Composer 2.5. Under the hood it might pick a different model.
I added your report to the others in this thread. No ETA for a fix yet.