H1 Transfer Issues

[hangover]

I am having approved I-140 from my current employer. My 6 years of H1 will be completed by September 2017. I am working on a Long term project and I want to transfer my H1 to new employer with the same client. I am entering into 6th year of H1 soon.

 

How many years of H1 extension will I get? 

3 years extension or till end of 6th year of H1. My client will provide the documents stating I can work on project for atleast 3 more years.

 

Thanks.