Most of the OPT students, especially from India, will be working for IT consulting firms where the student will be trained and placed at one of their client locations. This is called EVC (Employer-Vendor-Client) or EVVC model accordingly, where your Employer, Client and any vendors between them are the entities involving in your placement and your actual work location is the client location.
Following is the text from the govt's Federal register's website, which talks about the employment model restriction for OPT Employment.
Source: New Rule text for STEM OPT
The text in bold clearly says two things -
1) You must be hired by an employer as a real employee/full-time employee. (Working at 3rd party client site for 40 hrs throughout the period will not establish you as a bone fide employee)
2) Your Practical training experience (throughout OPT period) must be given by your employer - not by a client or your vendor.
So, the EVC or EVV...C business models will disqualify you for 24 month OPT extension facility.
Few other things from the new STEM extension rule are -
1) Voluntary (Un-paid) employment is not eligible for STEM extension. So you have to get paid all the time during your whole OPT period.
2) You need to submit I-983 form to the DSO.
3) Total allowable unemployment period during OPT and OPT extension is increased to 150 days.
Student planning to applying for STEM OPT extension are advised to work with your employer and lawyer to check if your employment is eligible for extension or not.
From now onward there might be a rise is students who want to applying for full time with real american companies.