L123: Remove C++ OpenCensus and dependent APIs

L123-remove-cpp-opencensus-apis.md

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+## L123: Deprecate and Remove C++ OpenCensus and dependent APIs
+
+*   Author(s): Yash Tibrewal (@yashykt)
+*   Approver: Mark Roth (@markdroth) , Esun Kim (@veblush)
+*   Status: In Review
+*   Implemented in: C++
+*   Last updated: May 13, 2025
+*   Discussion at: https://groups.google.com/g/grpc-io/c/ASVIZhcZgl0
+
+## Abstract
+
+Remove gRPC C++ OpenCensus and dependent APIs.
+
+## Background
+
+OpenCensus was
+[sunsetted in May, 2023](https://opentelemetry.io/blog/2023/sunsetting-opencensus/),
+and the
+[C++ OpenCensus repository](https://github.com/census-instrumentation/opencensus-cpp)
+has been archived (no longer maintained).
+
+Furthermore, the last available commit of OpenCensus C++ does not build with the
+[latest candidate release of the Abseil library](https://github.com/abseil/abseil-cpp/releases/tag/20250512.rc1)
+(OpenCensus C++ relied on internal headers and methods from Abseil.)
+
+## Proposal
+
+Deprecate the
+[C++ OpenCensus](https://github.com/grpc/grpc/blob/v1.72.x/include/grpcpp/opencensus.h)
+and dependent
+[gRPC C++ GCP Observability](https://github.com/grpc/grpc/blob/master/include/grpcpp/ext/gcp_observability.h)
+APIs and remove them in a subsequent release. Users still utilizing OpenCensus
+APIs should migrate to OpenTelemetry.
+
+## Rationale
+
+Given gRPC C++'s dependency on Abseil, maintaining OpenCensus support in future
+versions is not feasible. Deleting these APIs will allow gRPC C++ users to
+upgrade the version of the Abseil library used.
+
+## Implementation
+
+https://github.com/grpc/grpc/pull/39554 marks these APIs as deprecated. A
+subsequent release will delete these APIs.