Intel C/C++ compiler is provided as a part of three products.
This is a paid version but you can get it free if you were a Student/Classroom Educators/Open-Source Contributor.
For more info of pricing please visit https://software.intel.com/en-us/parallel-studio-xe
2) System Studio
Here you can configure and install only the C++ compiler. Intel provides a free license file that is valid for one year and thereafter you have to refresh the license.
For more info and download please visit https://software.intel.com/en-us/system-studio/choose-download
3)Intel OneApi HPC toolkit:
Intel provides a free C/C++ compiler as a part of its OneAPI Products. You have to download both Basekit and HPC kit for the compiler.
For more info and downloads visit https://software.intel.com/en-us/oneapi/base-kit
You can choose any one of them based on your requirements.
(I am not from Intel)
The purchased license (from my experience) includes 1 year of updates and customer support. Afterwards, you can either:
a) update ($) to get an additional 1 year of updates and customer support
b) continue using (or update to the last available update issued prior to the anniversary of your support contract).
Note, while you do not have official support from Intel, members of this forum do provide support in the terms of programming suggestions and work arounds to compiler bugs. Your bug reports will often be addressed, though you will not be able to update without re-upping your subscription.