I didn't actually need the pinyin conversion (I implement that myself), it was just a test to see how well LLMs* were progressing at "out-of-domain" tasks. I always used recent newspaper headlines, so the possibility of finding matching character/pinyin pairs somewhere in the huge training set was negligible.
For this specific task, Chat-GPT is the first model I've come across that actually shows some ability to chain together concrete steps to form a task (i.e. look up character, fetch pinyin), rather than the simplistic "predict the next word in the sequence" in pure language models.
* Large Language Model - I know ChatGPT isn't a pure language model (which probably explains why it performs so much better), but I don't know what we're calling these models now so I'm sticking with LLM for now.