This document explains how to use Abseil throughout gRPC. Note that this isn't supposed to explain general usage of Abseil.
gRPC intends to use the LTS versions of Abseil only because it simplifies dependency management. Abseil is being distributed via package distribution systems such as vcpkg and cocoapods. If gRPC depends on the certain version that aren't registered, gRPC in that system cannot get the right version of Abseil when being built, resulting in a build failure. Therefore, gRPC will use the LTS version only, preferably the latest one.
Most of Abseil libraries are okay to use but there are some exceptions because they're not going well yet on some of our test machinaries or platforms it supports. The following is a list of targets that are NOT ready to use.
absl/synchronization:*: This will be ready from the LTS version in 2021.absl/random: WIP.absl/types:variant: WIP.You can use Abseil in gRPC Core and gRPC C++. But you cannot use it in the public interface of gRPC C++ because i) it doesn't gurantee no breaking API changes like gRPC C++ does and ii) it may make users change their build system to address Abseil.