According to this KB article it seems to be compatible since Update Rollup 8:
Here is what I have tried so far and all of these worked:
- Creating applications that talk to CRM compiled in 4.5 that reference the 4.0 assemblies included with the SDK
- Registering 4.5 compiled plugins using the plugin registration tool (also recompiled to 4.5).
- Using new .NET 4.5 functionality in plugins (required 4.5 framework to be installed on server and a server reboot)
Interestingly enough my first .NET 4.5 plugin fired successfully even though .NET 4.5 wasn't installed on the CRM server. You only need the 4.5 framework installed if you use new 4.5 functionality. When I added some new code functionality in my plugin it did fail on that line of code until I installed the 4.5 framework on the server and rebooted. That fixed the issue and the plugin fired normally.
I am wondering if anyone has found anything that doesn't work so far? Let me know!