New Features

resolver: provide method, AuthorityOverrider, to allow resolver.Builders to override the default authority for a ClientConn. (EXPERIMENTAL) (#6752)
- Special Thanks: @Aditya-Sood
xds: add support for mTLS Credentials in xDS bootstrap (gRFC A65) (#6757)
- Special Thanks: @atollena
server: add grpc.WaitForHandlers ServerOption to cause Server.Stop to block until method handlers return. (EXPERIMENTAL) (#6922)

Performance Improvements

grpc: skip compression of empty messages as an optimization (#6842)
- Special Thanks: @jroper
orca: use atomic pointer to improve performance in server metrics recorder (#6799)
- Special Thanks: @danielzhaotongliu

client: correctly enable TCP keepalives with OS defaults on windows (#6863)
- Special Thanks: @mmatczuk
server: change some stream operations to return UNAVAILABLE instead of UNKNOWN when underlying connection is broken (#6891)
- Special Thanks: @mustafasen81
server: fix GracefulStop to block until all method handlers return (v1.60 regression). (#6922)
server: fix two bugs that could lead to panics at shutdown when using NumStreamWorkers (EXPERIMENTAL). (#6856)
reflection: do not send invalid descriptors to clients for files that cannot be fully resolved (#6771)
- Special Thanks: @jhump
xds: don't fail channel/server startup when xds creds is specified, but bootstrap is missing certificate providers (#6848)
xds: Atomically read and write xDS security configuration client side (#6796)
xds/server: fix RDS handling for non-inline route configs (#6915)