To coincide with the release of Microsoft SQL Server 2014, Microsoft StreamInsight has been updated to version 2.3. StreamInsight 2.3 is strictly a licensing update to version 2.1 that allows you to use StreamInsight with a SQL Server 2014 license. Any code written against StreamInsight 2.1 works the same in version 2.3.
You can get a copy of StreamInsight 2.3 from the SQL Server 2014 Feature Pack located in the Microsoft Download Center: http://www.microsoft.com/en-us/download/details.aspx?id=42295
See the StreamInsight 2.3 documentation on MSDN for installation instructions: http://msdn.microsoft.com/en-us/library/ee378749(v=sql.111).aspx
Note: Microsoft SQL Server media normally includes a copy of StreamInsight, but the SQL Server 2014 media erroneously includes the wrong version of StreamInsight. You can get the correct version at the Download Center as described above. More information is available here: http://support.microsoft.com/kb/2971131.