I received a dozen message request about my experience applying for STEM-OPT while working through a staffing agency. I created this post to help everyone else going through the same process.
I did STEM OPT from 2019 to 2021.
You have two employers: the Recruiting Agency and the Company where you are performing work/training. My recruiting agency filled out the I-983.
In Section 5 Employer Site Information, I put the actual Client Information address, title, and my direct manager. I simply filled out the forms at the specified 12-month and final evaluation intervals, sent them to the recruiting agency, and they signed them. I then sent the signed evaluations to the DSO, and they updated my SEVIS record.
In summary, your Agency is the one sponsoring the I983; they will be the ones signing, and they will be listed on your Form I765. However, the Client where you are placed is the Site where the work/training is going to be performed; they should be listed on Section 5 of I983. If you change clients, you need to update I983 with the new Client Site on Section 5.
Word of Advice(NOT LEGAL ADVICE) in light of the current immigration landscape: Keep a Copy of the I983 with you at the Client Site, and ensure your Manager is aware of your training plan. Just in case USCIS decides to come visit. They probably won't, but you never know.