CounterStrikeSharp is licensed under the GNU General Public License, version 3. 

As a special exception to the GNU General Public License 3.0, the license holder
permits licensing of DERIVATIVE WORKS ONLY (that is, 
CounterStrikeSharp plugins and extensions, or any software built 
referencing published .NET packages) under the MIT license.

A copy of the GNU General Public License 3.0 is available in LICENSE.GPL3
A copy of the MIT License is available in LICENSE.MIT