I thought I'd start this thread so I document performance issues that I now see when using V21 and an external application that hooks into Alibre using the API. The background is that I created a C# application some years ago which takes PCB design files and creates a PCB part, then using a library of electronic components that I've built over the years, it then creates an assembly and adds the PCB part plus the electronic component parts. I have used this application extensively with version prior to V21 and it generally creates a complete PCB assembly in no more than 3 or 4 minutes. Today, I tried it with V21 for the first time and it is sooooooo slow. After it adds approx 20 electronic parts to the assembly, Alibre hangs for about 10 minutes then recovers and the process continues until it hangs again for a while. At the end of the process my application saves the new assembly. At that point, Alibre has become unresponsive for over an hour now. Task manager shows ... I can't kill either the Home or Assembly Workspace task, yet it's still consuming approx 10% of CPU time and the memory is slowly creeping up. I'm not asking for comment as to why this is doing it, this is really a post for me to document my findings and share that so that others may benefit. I'm going to set up a known project (i.e. a specific PCB design), I'm going to fully profile my application in order to get some metrics, then I'm going to test that 'benchmark' on V21 HOOPS, V21 Legacy, and an earlier version of Alibre. I think it's important to determine if newer releases of Alibre are actually providing improved or worse performance. We see some many post on here on how certain functions are slower than they used to be or slower than other applications, so now it's impacted me, I'm determined to create a known benchmark that all versions can be tested against. Now, I know this is something that Alibre hopefully do internally, but anything I find will be given to Alibre to assist them. I will share the benchmark application with them in order that they can debug and improve performance. Watch this space!