I now see gpt-4o-mini listed at https://platform.openai.com/docs/models/gpt-4o-mini

Looking at https://openai.com/index/gpt-4o-mini-advancing-cost-efficien... , gpt-4o-mini is better than gpt-3.5 but worse than gpt-4o, as was expected. gpt-4o-mini is cheaper than both, however. Independent third-party performance benchmarks will help.