v1.6.0 was mistagged and has been deleted. The binaries of v1.6.0 are effectively the same as v1.6.1.

Important Changes

Android users should no longer need -keeps in their ProGuard configuration (#2633)
gRPC is no longer using the current Thread’s “context ClassLoader” when searching for transport Providers (#2375). Instead it is using the current class’s ClassLoader. This should not break existing users and work out-of-the-box in a larger number of environments
Fix support for Google AppEngine Java 8 (#3296)
Log netty connection errors at FINE instead of SEVERE (#1768)
Update netty to 4.1.14 and tcnative to 2.0.5 (#3307)
Channel state API is now implemented via ManagedChannel.getState/notifyWhenStateChanged. This requires LoadBalancer support; custom LoadBalancers should be updated to call updateBalancingState() instead of updatePicker()
Referencing CallCredentials is now stable API (#3289). Implementing or consuming CallCredentials is still ExperimentalApi
New method ClientCallStreamObserver.cancel() allows clients to cancel RPCs without requiring using an interceptor or Context (#3115)

Features

Census ~~trace~~ tags propagation is now enabled by default, but only if the Census Impl is available in the classpath (#3294)
Update google-auth-library-oauth2-http to 0.7.0 (#3188)
Update io.opencensus:opencensus-api to 0.5.1 (#3204)
CallOptions now passed to ClientStreamTracer.newClientStreamTracer (#3276)
Allow custom hostname verifiers for OkHttp via OkHttpChannelBuilder.hostnameVerifier() (#3205)

Calls should no longer fail with the message “Channel requested transport to shut down” when Channel.shutdown() was not called. The calls may still fail, but will have a more accurate message (#3351)
Clean up Context class initialization to avoid circular class loading issues (#3203, #3191)
Fix keepalive bug that sent too many pings (#3274)
Fixed “onStreamAllocated was not called, but it seems the stream is active” warning (#3007)

Pseudo headers (headers that begin with “:”) can no longer be set or retrieved (#3114). This has been the documented API, but now is being enforced
The object returned by Context.attach() must be the one passed into detach() (#3292)
When NameResolver returns >= 1 balancer GRPCLB policy will be forced (grpc/grpc#10258)