Pro Tools 12.3 is now compatible with OS X El Capitan 10.11! System Requirements and Compatibility with Pro Tools 12.3 Software (more info)
Mac OS X 10.11-10.11.1 (El Capitan), 10.10.3-10.10.5 (Yosemite), 10.9.5 (Mavericks) and 10.8.5 (Mountain Lion). Windows 8.1 64-bit and Windows 7 64-bit - Note that Windows 10 qualification is still in progress. If using Pro Tools 12.3 with Avid Artist, S3, S5-Hybrid and MCPro on Mountain Lion or Mavericks you should install EuControl 3.2 or higher (My Artist Login). S6 owners should update to version 1.4.1 if using Pro Tools 12.0 or higher (Avid Account > My Products and Subscriptions > S6 Software Update > Show).
Read Me and What's New files
The Read Me file documents important compatibility information, known issues, error messages, issues resolved, etc.
HDX Firmware Update
|Attachment: What's New in Pro Tools 12.3.pdf
Attachment: Pro Tools 12.3 Read Me - Mac.pdf
Attachment: Pro Tools 12.3 Read Me - Windows.pdf