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
There are several aspects of the STEM OPT extension that do not make it apt for certain types of arrangements, including multiple employer arrangements, sole proprietorships, employment through “temp” agencies, employment through consulting firm arrangements that provide labor for hire, and other relationships that do not constitute a bona fide employer-employee relationship. One concern arises from the difficulty individuals employed through such arrangements would face in complying with, among other things, the training plan requirements of this rule. Another concern is the potential for visa fraud arising from such arrangements. Furthermore, evaluating the merits of such arrangements would be difficult and create additional burdens for DSOs. Accordingly, DHS clarifies that students cannot qualify for STEM OPT extensions unless they will be bona fide employees of the employer signing the Training Plan, and the employer that signs the Training Plan must be the same entity that employs the student and provides the practical training experience. DHS recognizes that this outcome is a departure from SEVP's April 23, 2010 Policy Guidance (1004-03).
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.