This NIP is not yet in main. Here is an overview of PRs referencing this NIP. 
NIP-76 Relay Read Permissions OPEN @vitorpamplona
Speedrunning Run Submission Event OPEN @BlueZTV
Key Change - NIP-76 CLOSED @arthurfranca
NIP-76: Private Channels -  Draft 2 - Includes Client Implementation and Tool kit library CLOSED @d-krause
First Draft of Proposed NIP-76: Trace Resistant Private Posts CLOSED @d-krause