Do fixed annuity rates generally track the federal prime rate, the Treasury bond rate, or some other financial metric?

Great question.

In a nutshell, keep an eye on 30 year U.S. mortgage rates.

Moshe Milevsky does a great job addressing this question in paper he co-authored last spring titled "The Annuity Duration Puzzle".

The authors' research shows that the relationship between fixed annuity prices and interest rates is not quite as straightforward as one might expect.

First, it seems that annuity prices take awhile to adjust to and reflect changes in interest rates.  The changes are certainly not instantaneous--they adjust over a period of several weeks and even months.

A second point is that the 30 year U.S. mortgage rate provides a "better" fit and indication of where annuity prices are headed than many other seemingly obvious benchmarks such as the 10 year swap rate.

Hope this is helpful.