> It’s 1 and a half year [1] says that the STEM OPT extension is 24 months on top of the 12 month OPT.

> Only if your employer has already applied for your H1B. Doesn't seem like so to me, the requirements for the extension are (from [1]): >> Have a degree in an eligible STEM field from a Student and Exchange Visitor Program-certified school that is accredited when the student submits their STEM OPT extension application to USCIS. >> Pursue their STEM OPT extension through an employer that is enrolled in USCIS's E-Verify employment eligibility verification program. >> Select a STEM OPT employer that provides the student with formal training and learning objectives. Work a minimum of 20 hours per week per employer.

[1]: https://studyinthestates.dhs.gov/stem-opt-extension-overview