There are a number of new features in 4.1:
- Improved Logging and Caching.
- New JSON-Formatted Response Properties.
- New Garbage Collector Statistics Log.
- 32-bit and 64-bit Web Policy Agent Package for IIS.
- Added Support for Windows built-in Secure Channel API.
- Relative URL Support in Access Denied Property.
- The agentadmin Command Now Returns Status Codes on Failure.
- Added Support for PKCS#12/PFX Client Certificate Files
There are many more key fixes in 4.1. I just counted - a total of 78 key fixes. Do also note of the known issues in 4.1.
The behavior of Web Agent 3.x and 4.x is different, as what I have recently encountered in a customer's site. If one is to upgrade from version 3.x to 4.x, please do remember to test, test and test.
In our case, there is an edge case which was not tested in Devt. We had to rollback in Prod the day the new agents were deployed.