[yuhongsun]

Two other tidbits on this:

1. There's a difference between relevance and usefulness that cross-encoders cannot capture. Imagine a thread with a bunch of people complaining about an exception and each comment is another mention of the exception. Now imagine another thread with one mention of the exception at the top, and a bunch of people offering solutions. If you query for the exception, LLMs will find the second thread more useful, but cross encoders will find the first one more relevant.

2. LLMs/GenAI models don't output a single value. They can use the tokens they output to "reason" about the usefulness of a doc. Eg. Rerankers are like tiny LLMs that are only allowed to output "yes" or "no", but instead you can use an LLM to do chain-of-thought and finally decide at the end.