To apply for Extension of Status or Change of Status in US, you need to submit form I-539 with USCIS. After USCIS reviews the I-539 form and related documentation tied to the extension or Change of Status request and approves the Extension of Status or COS, they will send out Approval Notice to the applicant. As part of the Approval notice, there will be an I-94 slip attached to the same that indicates the Status and validity of the Status of the individual. Below is a sample of the same I-94 given by USCIS for such requests.
Sample I-94 Attached to Approval Notice issued by USCIS
The I-94 slip is attached to the bottom of the Approval notice. It looks like below. There are two parts, the one on the right hand side is the actual I-94 card, the one on the let is for your personal records. It will indicate the same on the left one. The I-94 on the left hand side looks exactly like a typical Paper I-94 Card that you get, when you travel to US via road. It has I-94 Number on top of it, below that you have the Receipt Number that is tied to your application with USCIS and then your first and last name, date of birth and country of citizenship. You need to hand this I-94 portion, when you leave US. The expiry date of the I-94 indicates, how long you can stay in US on that given visa status. In below example, the Class of visa status is H4, which is the status extended / given by USCIS until that end date. Also, below we have another I-94 sample for Class H1B as well.