I had a repeatable process set up with o4-mini that gave very good results. It generated output in a structured format, and the results were fairly formulaic but good. I did a lot of runs of this process and observed a lot of output.

I set that process down for like 4 or 5 months and then came back to it after GPT 5 came out. o4-mini was literally unusable. I've seen it with my own eyes.