Even a short-term job calls for a resignation letter when it's time to leave. This template is also appropirate for contract work and freelancing.
As agreed upon when I accepted the short-term position at ABC Corp., I am now submitting my resignation.
I am available for short-term or contract work in the future. I hope that my passion for this industry was made clear during my time in your employ.
It's truly been a pleasure to work with your talented and energetic team.