diff --git a/.gitmodules b/.gitmodules
index bb4b749beee..06f1394df65 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -51,3 +51,6 @@
 [submodule "third_party/protoc-gen-validate"]
 	path = third_party/protoc-gen-validate
 	url = https://github.com/lyft/protoc-gen-validate.git
+[submodule "third_party/upb"]
+	path = third_party/upb
+	url = https://github.com/google/upb.git
diff --git a/AUTHORS b/AUTHORS
index 3e130afda2d..0e8797391f2 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,2 +1,3 @@
+Dropbox, Inc.
 Google Inc.
 WeWork Companies Inc.
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e8582d9af5e..1d14d5e0e3a 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -81,7 +81,7 @@ How to get your contributions merged smoothly and quickly.
   copyright holder for the contribution (yourself, if you are signing the
   individual CLA, or your company, for corporate CLAs) in the same PR as your
   contribution.  This needs to be done only once, for each company, or
-  individual.
+  individual. Please keep this file in alphabetical order.
  
 - Maintain **clean commit history** and use **meaningful commit messages**.
   PRs with messy commit history are difficult to review and won't be merged.
diff --git a/WORKSPACE b/WORKSPACE
index a547c24cbe2..cd2718204d1 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -1,45 +1,59 @@
-workspace(name="com_github_grpc_grpc")
+workspace(name = "com_github_grpc_grpc")
 
 load("//bazel:grpc_deps.bzl", "grpc_deps", "grpc_test_only_deps")
+
 grpc_deps()
+
 grpc_test_only_deps()
 
+register_execution_platforms(
+    "//third_party/toolchains:all",
+)
+
+register_toolchains(
+    "//third_party/toolchains:all",
+)
+
 new_http_archive(
-    name="cython",
-    sha256="d68138a2381afbdd0876c3cb2a22389043fa01c4badede1228ee073032b07a27",
-    urls=[
+    name = "cython",
+    build_file = "//third_party:cython.BUILD",
+    sha256 = "d68138a2381afbdd0876c3cb2a22389043fa01c4badede1228ee073032b07a27",
+    strip_prefix = "cython-c2b80d87658a8525ce091cbe146cb7eaa29fed5c",
+    urls = [
         "https://github.com/cython/cython/archive/c2b80d87658a8525ce091cbe146cb7eaa29fed5c.tar.gz",
     ],
-    strip_prefix="cython-c2b80d87658a8525ce091cbe146cb7eaa29fed5c",
-    build_file="//third_party:cython.BUILD",
 )
 
 load("//third_party/py:python_configure.bzl", "python_configure")
-python_configure(name="local_config_python")
+
+python_configure(name = "local_config_python")
 
 git_repository(
-    name="io_bazel_rules_python",
-    remote="https://github.com/bazelbuild/rules_python.git",
-    commit="8b5d0683a7d878b28fffe464779c8a53659fc645",
+    name = "io_bazel_rules_python",
+    commit = "8b5d0683a7d878b28fffe464779c8a53659fc645",
+    remote = "https://github.com/bazelbuild/rules_python.git",
 )
 
 load("@io_bazel_rules_python//python:pip.bzl", "pip_repositories", "pip_import")
 
 pip_repositories()
+
 pip_import(
-    name="grpc_python_dependencies",
-    requirements="//:requirements.bazel.txt",
+    name = "grpc_python_dependencies",
+    requirements = "//:requirements.bazel.txt",
 )
 
 load("@grpc_python_dependencies//:requirements.bzl", "pip_install")
+
 pip_install()
 
 # NOTE(https://github.com/pubref/rules_protobuf/pull/196): Switch to upstream repo after this gets merged.
 git_repository(
-    name="org_pubref_rules_protobuf",
-    remote="https://github.com/ghostwriternr/rules_protobuf",
-    tag="v0.8.2.1-alpha",
+    name = "org_pubref_rules_protobuf",
+    remote = "https://github.com/ghostwriternr/rules_protobuf",
+    tag = "v0.8.2.1-alpha",
 )
 
 load("@org_pubref_rules_protobuf//python:rules.bzl", "py_proto_repositories")
+
 py_proto_repositories()
diff --git a/bazel/grpc_build_system.bzl b/bazel/grpc_build_system.bzl
index 159ebd5d1fe..65fe5a10aa2 100644
--- a/bazel/grpc_build_system.bzl
+++ b/bazel/grpc_build_system.bzl
@@ -131,7 +131,7 @@ def grpc_proto_library(
         generate_mocks = generate_mocks,
     )
 
-def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data = [], uses_polling = True, language = "C++", size = "medium", timeout = "moderate", tags = []):
+def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data = [], uses_polling = True, language = "C++", size = "medium", timeout = "moderate", tags = [], exec_compatible_with = []):
     copts = []
     if language.upper() == "C":
         copts = if_not_windows(["-std=c99"])
@@ -145,6 +145,7 @@ def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data
         "linkopts": if_not_windows(["-pthread"]),
         "size": size,
         "timeout": timeout,
+        "exec_compatible_with": exec_compatible_with,
     }
     if uses_polling:
         native.cc_test(testonly = True, tags = ["manual"], **args)
@@ -162,6 +163,7 @@ def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data
                     "$(location %s)" % name,
                 ] + args["args"],
                 tags = tags,
+                exec_compatible_with = exec_compatible_with,
             )
     else:
         native.cc_test(**args)
diff --git a/bazel/grpc_deps.bzl b/bazel/grpc_deps.bzl
index 86268178554..e091e5abc06 100644
--- a/bazel/grpc_deps.bzl
+++ b/bazel/grpc_deps.bzl
@@ -8,6 +8,11 @@ def grpc_deps():
         actual = "@com_github_nanopb_nanopb//:nanopb",
     )
 
+    native.bind(
+        name = "upblib",
+        actual = "@upb//:upb",
+    )
+
     native.bind(
         name = "absl-base",
         actual = "@com_google_absl//absl/base",
@@ -184,6 +189,13 @@ def grpc_deps():
             url = "https://github.com/census-instrumentation/opencensus-cpp/archive/fdf0f308b1631bb4a942e32ba5d22536a6170274.tar.gz",
         )
 
+    if "upb" not in native.existing_rules():
+        native.http_archive(
+            name = "upb",
+            strip_prefix = "upb-9ce4a77f61c134bbed28bfd5be5cd7dc0e80f5e3",
+            url = "https://github.com/google/upb/archive/9ce4a77f61c134bbed28bfd5be5cd7dc0e80f5e3.tar.gz",
+        )
+
 
 # TODO: move some dependencies from "grpc_deps" here?
 def grpc_test_only_deps():
diff --git a/doc/grpc_release_schedule.md b/doc/grpc_release_schedule.md
new file mode 100644
index 00000000000..bacd3758593
--- /dev/null
+++ b/doc/grpc_release_schedule.md
@@ -0,0 +1,22 @@
+# gRPC Release Schedule
+
+Below is the release schedule for gRPC [Java](https://github.com/grpc/grpc-java/releases), [Go](https://github.com/grpc/grpc-go/releases) and [Core](https://github.com/grpc/grpc/releases) and its  dependent languages C++, C#, Objective-C, PHP, Python and Ruby.
+
+Releases are scheduled every six weeks on Tuesdays on a best effort basis. In some unavoidable situations a release may be delayed or a language may skip a release altogether and do the next release to catch up with other languages. See the past releases in the links above. A six-week cycle gives us a good balance between delivering new features/fixes quickly and keeping the release overhead low.
+
+Releases are cut from release branches. For Core and Java repos, the release branch is cut two weeks before the scheduled release date. For Go, the branch is cut just before the release. An RC (release candidate) is published for Core and its dependent languages just after the branch cut. This RC is later promoted to release version if no further changes are made to the release branch. We do our best to keep head of master branch stable at all times regardless of release schedule. Daily build packages from master branch for C#, PHP, Python, Ruby and Protoc plugins are published on [packages.grpc.io](https://packages.grpc.io/). If you depend on gRPC in production we recommend to set up your CI system to test the RCs and, if possible, the daily builds.
+
+Names of gRPC releases are [here](https://github.com/grpc/grpc/blob/master/doc/g_stands_for.md).
+
+Release |Scheduled Branch Cut|Scheduled Release Date
+--------|--------------------|-------------
+v1.17.0 |Nov 19, 2018   |Dec 4, 2018
+v1.18.0 |Jan 2, 2019   |Jan 15, 2019
+v1.19.0 |Feb 12, 2019   |Feb 26, 2019
+v1.20.0 |Mar 26, 2019   |Apr 9, 2019
+v1.21.0 |May 7, 2019   |May 21, 2019
+v1.22.0 |Jun 18, 2019   |Jul 2, 2019
+v1.23.0 |Jul 30, 2019   |Aug 13, 2019
+v1.24.0 |Sept 10, 2019   |Sept 24, 2019
+v1.25.0 |Oct 22, 2019   |Nov 5, 2019
+v1.26.0 |Dec 3, 2019   |Dec 17, 2019
diff --git a/include/grpc/impl/codegen/atm_gcc_sync.h b/include/grpc/impl/codegen/atm_gcc_sync.h
index c0010a3469d..728c3d5412f 100644
--- a/include/grpc/impl/codegen/atm_gcc_sync.h
+++ b/include/grpc/impl/codegen/atm_gcc_sync.h
@@ -26,6 +26,8 @@
 typedef intptr_t gpr_atm;
 #define GPR_ATM_MAX INTPTR_MAX
 #define GPR_ATM_MIN INTPTR_MIN
+#define GPR_ATM_INC_CAS_THEN(blah) blah
+#define GPR_ATM_INC_ADD_THEN(blah) blah
 
 #define GPR_ATM_COMPILE_BARRIER_() __asm__ __volatile__("" : : : "memory")
 
diff --git a/include/grpc/impl/codegen/atm_windows.h b/include/grpc/impl/codegen/atm_windows.h
index f6b27e5df70..c016b90095f 100644
--- a/include/grpc/impl/codegen/atm_windows.h
+++ b/include/grpc/impl/codegen/atm_windows.h
@@ -25,6 +25,8 @@
 typedef intptr_t gpr_atm;
 #define GPR_ATM_MAX INTPTR_MAX
 #define GPR_ATM_MIN INTPTR_MIN
+#define GPR_ATM_INC_CAS_THEN(blah) blah
+#define GPR_ATM_INC_ADD_THEN(blah) blah
 
 #define gpr_atm_full_barrier MemoryBarrier
 
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
index dc0e1f89ce6..7e70f1c28bd 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
@@ -749,7 +749,7 @@ void GrpcLb::BalancerCallState::OnBalancerMessageReceivedLocked(
     void* arg, grpc_error* error) {
   BalancerCallState* lb_calld = static_cast<BalancerCallState*>(arg);
   GrpcLb* grpclb_policy = lb_calld->grpclb_policy();
-  // Empty payload means the LB call was cancelled.
+  // Null payload means the LB call was cancelled.
   if (lb_calld != grpclb_policy->lb_calld_.get() ||
       lb_calld->recv_message_payload_ == nullptr) {
     lb_calld->Unref(DEBUG_LOCATION, "on_message_received");
@@ -803,54 +803,45 @@ void GrpcLb::BalancerCallState::OnBalancerMessageReceivedLocked(
         gpr_free(ipport);
       }
     }
-    /* update serverlist */
-    if (serverlist->num_servers > 0) {
-      // Start sending client load report only after we start using the
-      // serverlist returned from the current LB call.
-      if (lb_calld->client_stats_report_interval_ > 0 &&
-          lb_calld->client_stats_ == nullptr) {
-        lb_calld->client_stats_.reset(New<GrpcLbClientStats>());
-        // TODO(roth): We currently track this ref manually.  Once the
-        // ClosureRef API is ready, we should pass the RefCountedPtr<> along
-        // with the callback.
-        auto self = lb_calld->Ref(DEBUG_LOCATION, "client_load_report");
-        self.release();
-        lb_calld->ScheduleNextClientLoadReportLocked();
-      }
-      if (grpc_grpclb_serverlist_equals(grpclb_policy->serverlist_,
-                                        serverlist)) {
-        if (grpc_lb_glb_trace.enabled()) {
-          gpr_log(GPR_INFO,
-                  "[grpclb %p] Incoming server list identical to current, "
-                  "ignoring.",
-                  grpclb_policy);
-        }
-        grpc_grpclb_destroy_serverlist(serverlist);
-      } else { /* new serverlist */
-        if (grpclb_policy->serverlist_ != nullptr) {
-          /* dispose of the old serverlist */
-          grpc_grpclb_destroy_serverlist(grpclb_policy->serverlist_);
-        } else {
-          /* or dispose of the fallback */
-          grpc_lb_addresses_destroy(grpclb_policy->fallback_backend_addresses_);
-          grpclb_policy->fallback_backend_addresses_ = nullptr;
-          if (grpclb_policy->fallback_timer_callback_pending_) {
-            grpc_timer_cancel(&grpclb_policy->lb_fallback_timer_);
-          }
-        }
-        // and update the copy in the GrpcLb instance. This
-        // serverlist instance will be destroyed either upon the next
-        // update or when the GrpcLb instance is destroyed.
-        grpclb_policy->serverlist_ = serverlist;
-        grpclb_policy->serverlist_index_ = 0;
-        grpclb_policy->CreateOrUpdateRoundRobinPolicyLocked();
-      }
-    } else {
+    // Start sending client load report only after we start using the
+    // serverlist returned from the current LB call.
+    if (lb_calld->client_stats_report_interval_ > 0 &&
+        lb_calld->client_stats_ == nullptr) {
+      lb_calld->client_stats_.reset(New<GrpcLbClientStats>());
+      // TODO(roth): We currently track this ref manually.  Once the
+      // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+      // with the callback.
+      auto self = lb_calld->Ref(DEBUG_LOCATION, "client_load_report");
+      self.release();
+      lb_calld->ScheduleNextClientLoadReportLocked();
+    }
+    // Check if the serverlist differs from the previous one.
+    if (grpc_grpclb_serverlist_equals(grpclb_policy->serverlist_, serverlist)) {
       if (grpc_lb_glb_trace.enabled()) {
-        gpr_log(GPR_INFO, "[grpclb %p] Received empty server list, ignoring.",
+        gpr_log(GPR_INFO,
+                "[grpclb %p] Incoming server list identical to current, "
+                "ignoring.",
                 grpclb_policy);
       }
       grpc_grpclb_destroy_serverlist(serverlist);
+    } else {  // New serverlist.
+      if (grpclb_policy->serverlist_ != nullptr) {
+        // Dispose of the old serverlist.
+        grpc_grpclb_destroy_serverlist(grpclb_policy->serverlist_);
+      } else {
+        // Dispose of the fallback.
+        grpc_lb_addresses_destroy(grpclb_policy->fallback_backend_addresses_);
+        grpclb_policy->fallback_backend_addresses_ = nullptr;
+        if (grpclb_policy->fallback_timer_callback_pending_) {
+          grpc_timer_cancel(&grpclb_policy->lb_fallback_timer_);
+        }
+      }
+      // Update the serverlist in the GrpcLb instance. This serverlist
+      // instance will be destroyed either upon the next update or when the
+      // GrpcLb instance is destroyed.
+      grpclb_policy->serverlist_ = serverlist;
+      grpclb_policy->serverlist_index_ = 0;
+      grpclb_policy->CreateOrUpdateRoundRobinPolicyLocked();
     }
   } else {
     // No valid initial response or serverlist found.
@@ -1583,7 +1574,7 @@ void GrpcLb::AddPendingPick(PendingPick* pp) {
 bool GrpcLb::PickFromRoundRobinPolicyLocked(bool force_async, PendingPick* pp,
                                             grpc_error** error) {
   // Check for drops if we are not using fallback backend addresses.
-  if (serverlist_ != nullptr) {
+  if (serverlist_ != nullptr && serverlist_->num_servers > 0) {
     // Look at the index into the serverlist to see if we should drop this call.
     grpc_grpclb_server* server = serverlist_->servers[serverlist_index_++];
     if (serverlist_index_ == serverlist_->num_servers) {
@@ -1681,7 +1672,6 @@ grpc_channel_args* GrpcLb::CreateRoundRobinPolicyArgsLocked() {
   grpc_lb_addresses* addresses;
   bool is_backend_from_grpclb_load_balancer = false;
   if (serverlist_ != nullptr) {
-    GPR_ASSERT(serverlist_->num_servers > 0);
     addresses = ProcessServerlist(serverlist_);
     is_backend_from_grpclb_load_balancer = true;
   } else {
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.cc b/src/core/ext/transport/chttp2/transport/chttp2_transport.cc
index b1b8c0083b1..99c675f503a 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.cc
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.cc
@@ -1390,6 +1390,7 @@ static void perform_stream_op_locked(void* stream_op,
   GRPC_STATS_INC_HTTP2_OP_BATCHES();
 
   s->context = op->payload->context;
+  s->traced = op->is_traced;
   if (grpc_http_trace.enabled()) {
     char* str = grpc_transport_stream_op_batch_string(op);
     gpr_log(GPR_INFO, "perform_stream_op_locked: %s; on_complete = %p", str,
diff --git a/src/core/ext/transport/chttp2/transport/internal.h b/src/core/ext/transport/chttp2/transport/internal.h
index 1c79cf63531..aeaa4935ad7 100644
--- a/src/core/ext/transport/chttp2/transport/internal.h
+++ b/src/core/ext/transport/chttp2/transport/internal.h
@@ -642,10 +642,10 @@ struct grpc_chttp2_stream {
   /** Whether bytes stored in unprocessed_incoming_byte_stream is decompressed
    */
   bool unprocessed_incoming_frames_decompressed = false;
-  /** gRPC header bytes that are already decompressed */
-  size_t decompressed_header_bytes = 0;
   /** Whether the bytes needs to be traced using Fathom */
   bool traced = false;
+  /** gRPC header bytes that are already decompressed */
+  size_t decompressed_header_bytes = 0;
 };
 
 /** Transport writing call flow:
diff --git a/src/core/lib/gprpp/inlined_vector.h b/src/core/lib/gprpp/inlined_vector.h
index 65c2b9634f2..66dc751a567 100644
--- a/src/core/lib/gprpp/inlined_vector.h
+++ b/src/core/lib/gprpp/inlined_vector.h
@@ -100,10 +100,7 @@ class InlinedVector {
   void reserve(size_t capacity) {
     if (capacity > capacity_) {
       T* new_dynamic = static_cast<T*>(gpr_malloc(sizeof(T) * capacity));
-      for (size_t i = 0; i < size_; ++i) {
-        new (&new_dynamic[i]) T(std::move(data()[i]));
-        data()[i].~T();
-      }
+      move_elements(data(), new_dynamic, size_);
       gpr_free(dynamic_);
       dynamic_ = new_dynamic;
       capacity_ = capacity;
@@ -131,13 +128,25 @@ class InlinedVector {
     size_--;
   }
 
+  size_t size() const { return size_; }
+  bool empty() const { return size_ == 0; }
+
+  size_t capacity() const { return capacity_; }
+
+  void clear() {
+    destroy_elements();
+    init_data();
+  }
+
+ private:
   void copy_from(const InlinedVector& v) {
-    // if v is allocated, copy over the buffer.
+    // if v is allocated, make sure we have enough capacity.
     if (v.dynamic_ != nullptr) {
       reserve(v.capacity_);
-      memcpy(dynamic_, v.dynamic_, v.size_ * sizeof(T));
-    } else {
-      memcpy(inline_, v.inline_, v.size_ * sizeof(T));
+    }
+    // copy over elements
+    for (size_t i = 0; i < v.size_; ++i) {
+      new (&(data()[i])) T(v[i]);
     }
     // copy over metadata
     size_ = v.size_;
@@ -145,11 +154,12 @@ class InlinedVector {
   }
 
   void move_from(InlinedVector& v) {
-    // if v is allocated, then we steal its buffer, else we copy it.
+    // if v is allocated, then we steal its dynamic array; otherwise, we
+    // move the elements individually.
     if (v.dynamic_ != nullptr) {
       dynamic_ = v.dynamic_;
     } else {
-      memcpy(inline_, v.inline_, v.size_ * sizeof(T));
+      move_elements(v.data(), data(), v.size_);
     }
     // copy over metadata
     size_ = v.size_;
@@ -158,17 +168,13 @@ class InlinedVector {
     v.init_data();
   }
 
-  size_t size() const { return size_; }
-  bool empty() const { return size_ == 0; }
-
-  size_t capacity() const { return capacity_; }
-
-  void clear() {
-    destroy_elements();
-    init_data();
+  static void move_elements(T* src, T* dst, size_t num_elements) {
+    for (size_t i = 0; i < num_elements; ++i) {
+      new (&dst[i]) T(std::move(src[i]));
+      src[i].~T();
+    }
   }
 
- private:
   void init_data() {
     dynamic_ = nullptr;
     size_ = 0;
diff --git a/src/core/lib/gprpp/ref_counted.h b/src/core/lib/gprpp/ref_counted.h
index e366445bff4..98de1a3653f 100644
--- a/src/core/lib/gprpp/ref_counted.h
+++ b/src/core/lib/gprpp/ref_counted.h
@@ -21,6 +21,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include <grpc/support/atm.h>
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
 
@@ -76,12 +77,15 @@ class RefCount {
   constexpr explicit RefCount(Value init = 1) : value_(init) {}
 
   // Increases the ref-count by `n`.
-  void Ref(Value n = 1) { value_.fetch_add(n, std::memory_order_relaxed); }
+  void Ref(Value n = 1) {
+    GPR_ATM_INC_ADD_THEN(value_.fetch_add(n, std::memory_order_relaxed));
+  }
 
   // Similar to Ref() with an assert on the ref-count being non-zero.
   void RefNonZero() {
 #ifndef NDEBUG
-    const Value prior = value_.fetch_add(1, std::memory_order_relaxed);
+    const Value prior =
+        GPR_ATM_INC_ADD_THEN(value_.fetch_add(1, std::memory_order_relaxed));
     assert(prior > 0);
 #else
     Ref();
@@ -90,7 +94,8 @@ class RefCount {
 
   // Decrements the ref-count and returns true if the ref-count reaches 0.
   bool Unref() {
-    const Value prior = value_.fetch_sub(1, std::memory_order_acq_rel);
+    const Value prior =
+        GPR_ATM_INC_ADD_THEN(value_.fetch_sub(1, std::memory_order_acq_rel));
     GPR_DEBUG_ASSERT(prior > 0);
     return prior == 1;
   }
diff --git a/src/core/lib/iomgr/ev_epoll1_linux.cc b/src/core/lib/iomgr/ev_epoll1_linux.cc
index 38571b1957b..4b8c891e9b0 100644
--- a/src/core/lib/iomgr/ev_epoll1_linux.cc
+++ b/src/core/lib/iomgr/ev_epoll1_linux.cc
@@ -1242,6 +1242,8 @@ static void pollset_set_del_pollset_set(grpc_pollset_set* bag,
  * Event engine binding
  */
 
+static void shutdown_background_closure(void) {}
+
 static void shutdown_engine(void) {
   fd_global_shutdown();
   pollset_global_shutdown();
@@ -1255,6 +1257,7 @@ static void shutdown_engine(void) {
 static const grpc_event_engine_vtable vtable = {
     sizeof(grpc_pollset),
     true,
+    false,
 
     fd_create,
     fd_wrapped_fd,
@@ -1284,6 +1287,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    shutdown_background_closure,
     shutdown_engine,
 };
 
diff --git a/src/core/lib/iomgr/ev_epollex_linux.cc b/src/core/lib/iomgr/ev_epollex_linux.cc
index 06a382c5560..7a4870db785 100644
--- a/src/core/lib/iomgr/ev_epollex_linux.cc
+++ b/src/core/lib/iomgr/ev_epollex_linux.cc
@@ -1604,6 +1604,8 @@ static void pollset_set_del_pollset_set(grpc_pollset_set* bag,
  * Event engine binding
  */
 
+static void shutdown_background_closure(void) {}
+
 static void shutdown_engine(void) {
   fd_global_shutdown();
   pollset_global_shutdown();
@@ -1612,6 +1614,7 @@ static void shutdown_engine(void) {
 static const grpc_event_engine_vtable vtable = {
     sizeof(grpc_pollset),
     true,
+    false,
 
     fd_create,
     fd_wrapped_fd,
@@ -1641,6 +1644,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    shutdown_background_closure,
     shutdown_engine,
 };
 
diff --git a/src/core/lib/iomgr/ev_poll_posix.cc b/src/core/lib/iomgr/ev_poll_posix.cc
index 16562538a63..67cbfbbd021 100644
--- a/src/core/lib/iomgr/ev_poll_posix.cc
+++ b/src/core/lib/iomgr/ev_poll_posix.cc
@@ -1782,6 +1782,8 @@ static void global_cv_fd_table_shutdown() {
  * event engine binding
  */
 
+static void shutdown_background_closure(void) {}
+
 static void shutdown_engine(void) {
   pollset_global_shutdown();
   if (grpc_cv_wakeup_fds_enabled()) {
@@ -1796,6 +1798,7 @@ static void shutdown_engine(void) {
 static const grpc_event_engine_vtable vtable = {
     sizeof(grpc_pollset),
     false,
+    false,
 
     fd_create,
     fd_wrapped_fd,
@@ -1825,6 +1828,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    shutdown_background_closure,
     shutdown_engine,
 };
 
diff --git a/src/core/lib/iomgr/ev_posix.cc b/src/core/lib/iomgr/ev_posix.cc
index 8a7dc7b004a..32d1b6c43ef 100644
--- a/src/core/lib/iomgr/ev_posix.cc
+++ b/src/core/lib/iomgr/ev_posix.cc
@@ -36,6 +36,7 @@
 #include "src/core/lib/iomgr/ev_epoll1_linux.h"
 #include "src/core/lib/iomgr/ev_epollex_linux.h"
 #include "src/core/lib/iomgr/ev_poll_posix.h"
+#include "src/core/lib/iomgr/internal_errqueue.h"
 
 grpc_core::TraceFlag grpc_polling_trace(false,
                                         "polling"); /* Disabled by default */
@@ -236,19 +237,22 @@ void grpc_event_engine_shutdown(void) {
 }
 
 bool grpc_event_engine_can_track_errors(void) {
-/* Only track errors if platform supports errqueue. */
-#ifdef GRPC_LINUX_ERRQUEUE
-  return g_event_engine->can_track_err;
-#else
+  /* Only track errors if platform supports errqueue. */
+  if (grpc_core::kernel_supports_errqueue()) {
+    return g_event_engine->can_track_err;
+  }
   return false;
-#endif /* GRPC_LINUX_ERRQUEUE */
+}
+
+bool grpc_event_engine_run_in_background(void) {
+  return g_event_engine->run_in_background;
 }
 
 grpc_fd* grpc_fd_create(int fd, const char* name, bool track_err) {
   GRPC_POLLING_API_TRACE("fd_create(%d, %s, %d)", fd, name, track_err);
   GRPC_FD_TRACE("fd_create(%d, %s, %d)", fd, name, track_err);
-  return g_event_engine->fd_create(fd, name,
-                                   track_err && g_event_engine->can_track_err);
+  return g_event_engine->fd_create(
+      fd, name, track_err && grpc_event_engine_can_track_errors());
 }
 
 int grpc_fd_wrapped_fd(grpc_fd* fd) {
@@ -395,4 +399,8 @@ void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd) {
   g_event_engine->pollset_set_del_fd(pollset_set, fd);
 }
 
+void grpc_shutdown_background_closure(void) {
+  g_event_engine->shutdown_background_closure();
+}
+
 #endif  // GRPC_POSIX_SOCKET_EV
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index b8fb8f534b4..812c7a0f0f8 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -42,6 +42,7 @@ typedef struct grpc_fd grpc_fd;
 typedef struct grpc_event_engine_vtable {
   size_t pollset_size;
   bool can_track_err;
+  bool run_in_background;
 
   grpc_fd* (*fd_create)(int fd, const char* name, bool track_err);
   int (*fd_wrapped_fd)(grpc_fd* fd);
@@ -79,6 +80,7 @@ typedef struct grpc_event_engine_vtable {
   void (*pollset_set_add_fd)(grpc_pollset_set* pollset_set, grpc_fd* fd);
   void (*pollset_set_del_fd)(grpc_pollset_set* pollset_set, grpc_fd* fd);
 
+  void (*shutdown_background_closure)(void);
   void (*shutdown_engine)(void);
 } grpc_event_engine_vtable;
 
@@ -101,6 +103,11 @@ const char* grpc_get_poll_strategy_name();
  */
 bool grpc_event_engine_can_track_errors();
 
+/* Returns true if polling engine runs in the background, false otherwise.
+ * Currently only 'epollbg' runs in the background.
+ */
+bool grpc_event_engine_run_in_background();
+
 /* Create a wrapped file descriptor.
    Requires fd is a non-blocking file descriptor.
    \a track_err if true means that error events would be tracked separately
@@ -174,6 +181,9 @@ void grpc_pollset_add_fd(grpc_pollset* pollset, struct grpc_fd* fd);
 void grpc_pollset_set_add_fd(grpc_pollset_set* pollset_set, grpc_fd* fd);
 void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd);
 
+/* Shut down all the closures registered in the background poller. */
+void grpc_shutdown_background_closure();
+
 /* override to allow tests to hook poll() usage */
 typedef int (*grpc_poll_function_type)(struct pollfd*, nfds_t, int);
 extern grpc_poll_function_type grpc_poll_function;
diff --git a/src/core/lib/iomgr/internal_errqueue.cc b/src/core/lib/iomgr/internal_errqueue.cc
index 99c22e90555..982d709f094 100644
--- a/src/core/lib/iomgr/internal_errqueue.cc
+++ b/src/core/lib/iomgr/internal_errqueue.cc
@@ -20,17 +20,50 @@
 
 #include "src/core/lib/iomgr/port.h"
 
+#include <grpc/impl/codegen/log.h>
 #include "src/core/lib/iomgr/internal_errqueue.h"
 
 #ifdef GRPC_POSIX_SOCKET_TCP
 
-bool kernel_supports_errqueue() {
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/utsname.h>
+
+namespace grpc_core {
+static bool errqueue_supported = false;
+
+bool kernel_supports_errqueue() { return errqueue_supported; }
+
+void grpc_errqueue_init() {
+/* Both-compile time and run-time linux kernel versions should be atleast 4.0.0
+ */
 #ifdef LINUX_VERSION_CODE
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 0, 0)
-  return true;
+  struct utsname buffer;
+  if (uname(&buffer) != 0) {
+    gpr_log(GPR_ERROR, "uname: %s", strerror(errno));
+    return;
+  }
+  char* release = buffer.release;
+  if (release == nullptr) {
+    return;
+  }
+
+  if (strtol(release, nullptr, 10) >= 4) {
+    errqueue_supported = true;
+  } else {
+    gpr_log(GPR_DEBUG, "ERRQUEUE support not enabled");
+  }
 #endif /* LINUX_VERSION_CODE <= KERNEL_VERSION(4, 0, 0) */
 #endif /* LINUX_VERSION_CODE */
-  return false;
 }
+} /* namespace grpc_core */
+
+#else
+
+namespace grpc_core {
+void grpc_errqueue_init() {}
+} /* namespace grpc_core */
 
 #endif /* GRPC_POSIX_SOCKET_TCP */
diff --git a/src/core/lib/iomgr/internal_errqueue.h b/src/core/lib/iomgr/internal_errqueue.h
index 9d122808f9b..f8644c2536c 100644
--- a/src/core/lib/iomgr/internal_errqueue.h
+++ b/src/core/lib/iomgr/internal_errqueue.h
@@ -76,8 +76,14 @@ constexpr uint32_t kTimestampingRecordingOptions =
  * Currently allowing only linux kernels above 4.0.0
  */
 bool kernel_supports_errqueue();
-}  // namespace grpc_core
+
+} /* namespace grpc_core */
 
 #endif /* GRPC_POSIX_SOCKET_TCP */
 
+namespace grpc_core {
+/* Initializes errqueue support */
+void grpc_errqueue_init();
+} /* namespace grpc_core */
+
 #endif /* GRPC_CORE_LIB_IOMGR_INTERNAL_ERRQUEUE_H */
diff --git a/src/core/lib/iomgr/iomgr.cc b/src/core/lib/iomgr/iomgr.cc
index 30b68db4df7..eb29973514f 100644
--- a/src/core/lib/iomgr/iomgr.cc
+++ b/src/core/lib/iomgr/iomgr.cc
@@ -36,6 +36,7 @@
 #include "src/core/lib/iomgr/buffer_list.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/iomgr/executor.h"
+#include "src/core/lib/iomgr/internal_errqueue.h"
 #include "src/core/lib/iomgr/iomgr_internal.h"
 #include "src/core/lib/iomgr/network_status_tracker.h"
 #include "src/core/lib/iomgr/timer.h"
@@ -58,6 +59,7 @@ void grpc_iomgr_init() {
   g_root_object.name = (char*)"root";
   grpc_network_status_init();
   grpc_iomgr_platform_init();
+  grpc_core::grpc_errqueue_init();
 }
 
 void grpc_iomgr_start() { grpc_timer_manager_init(); }
@@ -155,6 +157,10 @@ void grpc_iomgr_shutdown() {
   gpr_cv_destroy(&g_rcv);
 }
 
+void grpc_iomgr_shutdown_background_closure() {
+  grpc_iomgr_platform_shutdown_background_closure();
+}
+
 void grpc_iomgr_register_object(grpc_iomgr_object* obj, const char* name) {
   obj->name = gpr_strdup(name);
   gpr_mu_lock(&g_mu);
diff --git a/src/core/lib/iomgr/iomgr.h b/src/core/lib/iomgr/iomgr.h
index 537ef8a6ffe..8ea9289e068 100644
--- a/src/core/lib/iomgr/iomgr.h
+++ b/src/core/lib/iomgr/iomgr.h
@@ -35,6 +35,10 @@ void grpc_iomgr_start();
  * exec_ctx. */
 void grpc_iomgr_shutdown();
 
+/** Signals the intention to shutdown all the closures registered in the
+ * background poller. */
+void grpc_iomgr_shutdown_background_closure();
+
 /* Exposed only for testing */
 size_t grpc_iomgr_count_objects_for_testing();
 
diff --git a/src/core/lib/iomgr/iomgr_custom.cc b/src/core/lib/iomgr/iomgr_custom.cc
index d34c8e7cd14..4b112c9097f 100644
--- a/src/core/lib/iomgr/iomgr_custom.cc
+++ b/src/core/lib/iomgr/iomgr_custom.cc
@@ -40,9 +40,11 @@ static void iomgr_platform_init(void) {
 }
 static void iomgr_platform_flush(void) {}
 static void iomgr_platform_shutdown(void) { grpc_pollset_global_shutdown(); }
+static void iomgr_platform_shutdown_background_closure(void) {}
 
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_custom_iomgr_init(grpc_socket_vtable* socket,
                             grpc_custom_resolver_vtable* resolver,
diff --git a/src/core/lib/iomgr/iomgr_internal.cc b/src/core/lib/iomgr/iomgr_internal.cc
index 32dbabb79dc..b6c9211865d 100644
--- a/src/core/lib/iomgr/iomgr_internal.cc
+++ b/src/core/lib/iomgr/iomgr_internal.cc
@@ -41,3 +41,7 @@ void grpc_iomgr_platform_init() { iomgr_platform_vtable->init(); }
 void grpc_iomgr_platform_flush() { iomgr_platform_vtable->flush(); }
 
 void grpc_iomgr_platform_shutdown() { iomgr_platform_vtable->shutdown(); }
+
+void grpc_iomgr_platform_shutdown_background_closure() {
+  iomgr_platform_vtable->shutdown_background_closure();
+}
diff --git a/src/core/lib/iomgr/iomgr_internal.h b/src/core/lib/iomgr/iomgr_internal.h
index b011d9c7b19..bca7409907f 100644
--- a/src/core/lib/iomgr/iomgr_internal.h
+++ b/src/core/lib/iomgr/iomgr_internal.h
@@ -35,6 +35,7 @@ typedef struct grpc_iomgr_platform_vtable {
   void (*init)(void);
   void (*flush)(void);
   void (*shutdown)(void);
+  void (*shutdown_background_closure)(void);
 } grpc_iomgr_platform_vtable;
 
 void grpc_iomgr_register_object(grpc_iomgr_object* obj, const char* name);
@@ -52,6 +53,9 @@ void grpc_iomgr_platform_flush(void);
 /** tear down all platform specific global iomgr structures */
 void grpc_iomgr_platform_shutdown(void);
 
+/** shut down all the closures registered in the background poller */
+void grpc_iomgr_platform_shutdown_background_closure(void);
+
 bool grpc_iomgr_abort_on_leaks(void);
 
 #endif /* GRPC_CORE_LIB_IOMGR_IOMGR_INTERNAL_H */
diff --git a/src/core/lib/iomgr/iomgr_posix.cc b/src/core/lib/iomgr/iomgr_posix.cc
index ca7334c9a4b..9386adf060d 100644
--- a/src/core/lib/iomgr/iomgr_posix.cc
+++ b/src/core/lib/iomgr/iomgr_posix.cc
@@ -51,8 +51,13 @@ static void iomgr_platform_shutdown(void) {
   grpc_wakeup_fd_global_destroy();
 }
 
+static void iomgr_platform_shutdown_background_closure(void) {
+  grpc_shutdown_background_closure();
+}
+
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_set_default_iomgr_platform() {
   grpc_set_tcp_client_impl(&grpc_posix_tcp_client_vtable);
diff --git a/src/core/lib/iomgr/iomgr_posix_cfstream.cc b/src/core/lib/iomgr/iomgr_posix_cfstream.cc
index 235a9e0712f..552ef4309c8 100644
--- a/src/core/lib/iomgr/iomgr_posix_cfstream.cc
+++ b/src/core/lib/iomgr/iomgr_posix_cfstream.cc
@@ -54,8 +54,13 @@ static void iomgr_platform_shutdown(void) {
   grpc_wakeup_fd_global_destroy();
 }
 
+static void iomgr_platform_shutdown_background_closure(void) {
+  grpc_shutdown_background_closure();
+}
+
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_set_default_iomgr_platform() {
   char* enable_cfstream = getenv(grpc_cfstream_env_var);
diff --git a/src/core/lib/iomgr/iomgr_windows.cc b/src/core/lib/iomgr/iomgr_windows.cc
index cdef89cbf04..24ef0dba7b4 100644
--- a/src/core/lib/iomgr/iomgr_windows.cc
+++ b/src/core/lib/iomgr/iomgr_windows.cc
@@ -71,8 +71,11 @@ static void iomgr_platform_shutdown(void) {
   winsock_shutdown();
 }
 
+static void iomgr_platform_shutdown_background_closure(void) {}
+
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_set_default_iomgr_platform() {
   grpc_set_tcp_client_impl(&grpc_windows_tcp_client_vtable);
diff --git a/src/core/lib/iomgr/port.h b/src/core/lib/iomgr/port.h
index bf56a7298d2..c8046b21dcd 100644
--- a/src/core/lib/iomgr/port.h
+++ b/src/core/lib/iomgr/port.h
@@ -62,8 +62,7 @@
 #define GRPC_HAVE_UNIX_SOCKET 1
 #ifdef LINUX_VERSION_CODE
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 0, 0)
-/* TODO(yashykt): Re-enable once Fathom changes are commited.
-#define GRPC_LINUX_ERRQUEUE 1 */
+#define GRPC_LINUX_ERRQUEUE 1
 #endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(4, 0, 0) */
 #endif /* LINUX_VERSION_CODE */
 #define GRPC_LINUX_MULTIPOLL_WITH_EPOLL 1
diff --git a/src/core/lib/iomgr/tcp_posix.cc b/src/core/lib/iomgr/tcp_posix.cc
index cb4c9db7a68..606bfce6e73 100644
--- a/src/core/lib/iomgr/tcp_posix.cc
+++ b/src/core/lib/iomgr/tcp_posix.cc
@@ -260,10 +260,17 @@ static void notify_on_write(grpc_tcp* tcp) {
   if (grpc_tcp_trace.enabled()) {
     gpr_log(GPR_INFO, "TCP:%p notify_on_write", tcp);
   }
-  cover_self(tcp);
-  GRPC_CLOSURE_INIT(&tcp->write_done_closure,
-                    tcp_drop_uncovered_then_handle_write, tcp,
-                    grpc_schedule_on_exec_ctx);
+  if (grpc_event_engine_run_in_background()) {
+    // If there is a polling engine always running in the background, there is
+    // no need to run the backup poller.
+    GRPC_CLOSURE_INIT(&tcp->write_done_closure, tcp_handle_write, tcp,
+                      grpc_schedule_on_exec_ctx);
+  } else {
+    cover_self(tcp);
+    GRPC_CLOSURE_INIT(&tcp->write_done_closure,
+                      tcp_drop_uncovered_then_handle_write, tcp,
+                      grpc_schedule_on_exec_ctx);
+  }
   grpc_fd_notify_on_write(tcp->em_fd, &tcp->write_done_closure);
 }
 
@@ -740,7 +747,7 @@ static bool process_errors(grpc_tcp* tcp) {
         }
         return false;
       }
-      process_timestamp(tcp, &msg, cmsg);
+      cmsg = process_timestamp(tcp, &msg, cmsg);
     }
   }
 }
@@ -761,13 +768,11 @@ static void tcp_handle_error(void* arg /* grpc_tcp */, grpc_error* error) {
 
   /* We are still interested in collecting timestamps, so let's try reading
    * them. */
-  if (!process_errors(tcp)) {
-    /* This was not a timestamps error. This was an actual error. Set the
-     * read and write closures to be ready.
-     */
-    grpc_fd_set_readable(tcp->em_fd);
-    grpc_fd_set_writable(tcp->em_fd);
-  }
+  process_errors(tcp);
+  /* This might not a timestamps error. Set the read and write closures to be
+   * ready. */
+  grpc_fd_set_readable(tcp->em_fd);
+  grpc_fd_set_writable(tcp->em_fd);
   GRPC_CLOSURE_INIT(&tcp->error_closure, tcp_handle_error, tcp,
                     grpc_schedule_on_exec_ctx);
   grpc_fd_notify_on_error(tcp->em_fd, &tcp->error_closure);
diff --git a/src/core/lib/surface/init.cc b/src/core/lib/surface/init.cc
index 64d8222ce80..aa0cf58335f 100644
--- a/src/core/lib/surface/init.cc
+++ b/src/core/lib/surface/init.cc
@@ -175,8 +175,10 @@ void grpc_shutdown_internal(void* ignored) {
   }
   {
     grpc_core::ExecCtx exec_ctx(0);
+    grpc_iomgr_shutdown_background_closure();
     {
-      grpc_timer_manager_set_threading(false);  // shutdown timer_manager thread
+      grpc_timer_manager_set_threading(
+          false);  // shutdown timer_manager thread
       grpc_executor_shutdown();
       for (i = g_number_of_plugins; i >= 0; i--) {
         if (g_all_of_the_plugins[i].destroy != nullptr) {
diff --git a/src/core/lib/transport/transport.cc b/src/core/lib/transport/transport.cc
index cbdb77c8441..b32f9c6ec1a 100644
--- a/src/core/lib/transport/transport.cc
+++ b/src/core/lib/transport/transport.cc
@@ -27,6 +27,7 @@
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
 
+#include "src/core/lib/gpr/alloc.h"
 #include "src/core/lib/gpr/string.h"
 #include "src/core/lib/iomgr/executor.h"
 #include "src/core/lib/slice/slice_internal.h"
@@ -149,7 +150,7 @@ void grpc_transport_move_stats(grpc_transport_stream_stats* from,
 }
 
 size_t grpc_transport_stream_size(grpc_transport* transport) {
-  return transport->vtable->sizeof_stream;
+  return GPR_ROUND_UP_TO_ALIGNMENT_SIZE(transport->vtable->sizeof_stream);
 }
 
 void grpc_transport_destroy(grpc_transport* transport) {
diff --git a/src/core/lib/transport/transport.h b/src/core/lib/transport/transport.h
index edfa7030d13..5ce568834e9 100644
--- a/src/core/lib/transport/transport.h
+++ b/src/core/lib/transport/transport.h
@@ -129,7 +129,8 @@ struct grpc_transport_stream_op_batch {
         recv_initial_metadata(false),
         recv_message(false),
         recv_trailing_metadata(false),
-        cancel_stream(false) {}
+        cancel_stream(false),
+        is_traced(false) {}
 
   /** Should be scheduled when all of the non-recv operations in the batch
       are complete.
@@ -167,6 +168,9 @@ struct grpc_transport_stream_op_batch {
   /** Cancel this stream with the provided error */
   bool cancel_stream : 1;
 
+  /** Is this stream traced */
+  bool is_traced : 1;
+
   /***************************************************************************
    * remaining fields are initialized and used at the discretion of the
    * current handler of the op */
diff --git a/src/php/ext/grpc/php_grpc.c b/src/php/ext/grpc/php_grpc.c
index 492325b1e8b..111c6f4867d 100644
--- a/src/php/ext/grpc/php_grpc.c
+++ b/src/php/ext/grpc/php_grpc.c
@@ -171,11 +171,13 @@ void prefork() {
 }
 
 void postfork_child() {
+  TSRMLS_FETCH();
+
   // loop through persistant list and destroy all underlying grpc_channel objs
   destroy_grpc_channels();
 
   // clear completion queue
-  grpc_php_shutdown_completion_queue();
+  grpc_php_shutdown_completion_queue(TSRMLS_C);
 
   // clean-up grpc_core
   grpc_shutdown();
@@ -187,7 +189,7 @@ void postfork_child() {
 
   // restart grpc_core
   grpc_init();
-  grpc_php_init_completion_queue();
+  grpc_php_init_completion_queue(TSRMLS_C);
 
   // re-create grpc_channel and point wrapped to it
   // unlock wrapped grpc channel mutex
diff --git a/src/python/grpcio/grpc/__init__.py b/src/python/grpcio/grpc/__init__.py
index 88c5b6d5be5..6022fc3ef21 100644
--- a/src/python/grpcio/grpc/__init__.py
+++ b/src/python/grpcio/grpc/__init__.py
@@ -1723,7 +1723,7 @@ def server(thread_pool,
         handlers. The interceptors are given control in the order they are
         specified. This is an EXPERIMENTAL API.
       options: An optional list of key-value pairs (channel args in gRPC runtime)
-      to configure the channel.
+        to configure the channel.
       maximum_concurrent_rpcs: The maximum number of concurrent RPCs this server
         will service before returning RESOURCE_EXHAUSTED status, or None to
         indicate no limit.
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi
index 23428f0b0c0..5aaf31e36c2 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi
@@ -121,7 +121,6 @@ cdef extern from "grpc/grpc.h":
     GRPC_STATUS_DATA_LOSS
     GRPC_STATUS__DO_NOT_USE
 
-  const char *GRPC_ARG_PRIMARY_USER_AGENT_STRING
   const char *GRPC_ARG_ENABLE_CENSUS
   const char *GRPC_ARG_MAX_CONCURRENT_STREAMS
   const char *GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH
@@ -190,12 +189,6 @@ cdef extern from "grpc/grpc.h":
     size_t arguments_length "num_args"
     grpc_arg *arguments "args"
 
-  ctypedef enum grpc_compression_level:
-    GRPC_COMPRESS_LEVEL_NONE
-    GRPC_COMPRESS_LEVEL_LOW
-    GRPC_COMPRESS_LEVEL_MED
-    GRPC_COMPRESS_LEVEL_HIGH
-
   ctypedef enum grpc_stream_compression_level:
     GRPC_STREAM_COMPRESS_LEVEL_NONE
     GRPC_STREAM_COMPRESS_LEVEL_LOW
diff --git a/src/python/grpcio/grpc/_interceptor.py b/src/python/grpcio/grpc/_interceptor.py
index 43451140265..2a8ddd8ce42 100644
--- a/src/python/grpcio/grpc/_interceptor.py
+++ b/src/python/grpcio/grpc/_interceptor.py
@@ -232,8 +232,8 @@ class _UnaryUnaryMultiCallable(grpc.UnaryUnaryMultiCallable):
                     credentials=new_credentials,
                     wait_for_ready=new_wait_for_ready)
                 return _UnaryOutcome(response, call)
-            except grpc.RpcError:
-                raise
+            except grpc.RpcError as rpc_error:
+                return rpc_error
             except Exception as exception:  # pylint:disable=broad-except
                 return _FailureOutcome(exception, sys.exc_info()[2])
 
@@ -354,8 +354,8 @@ class _StreamUnaryMultiCallable(grpc.StreamUnaryMultiCallable):
                     credentials=new_credentials,
                     wait_for_ready=new_wait_for_ready)
                 return _UnaryOutcome(response, call)
-            except grpc.RpcError:
-                raise
+            except grpc.RpcError as rpc_error:
+                return rpc_error
             except Exception as exception:  # pylint:disable=broad-except
                 return _FailureOutcome(exception, sys.exc_info()[2])
 
diff --git a/src/ruby/lib/grpc/generic/service.rb b/src/ruby/lib/grpc/generic/service.rb
index 4764217406b..169a62f11d3 100644
--- a/src/ruby/lib/grpc/generic/service.rb
+++ b/src/ruby/lib/grpc/generic/service.rb
@@ -95,7 +95,7 @@ module GRPC
         rpc_descs[name] = RpcDesc.new(name, input, output,
                                       marshal_class_method,
                                       unmarshal_class_method)
-        define_method(GenericService.underscore(name.to_s).to_sym) do |_, _|
+        define_method(GenericService.underscore(name.to_s).to_sym) do |*|
           fail GRPC::BadStatus.new_status_exception(
             GRPC::Core::StatusCodes::UNIMPLEMENTED)
         end
diff --git a/src/ruby/spec/generic/rpc_server_spec.rb b/src/ruby/spec/generic/rpc_server_spec.rb
index 44a61340869..924d747a79c 100644
--- a/src/ruby/spec/generic/rpc_server_spec.rb
+++ b/src/ruby/spec/generic/rpc_server_spec.rb
@@ -342,6 +342,28 @@ describe GRPC::RpcServer do
         t.join
       end
 
+      it 'should return UNIMPLEMENTED on unimplemented ' \
+         'methods for client_streamer', server: true do
+        @srv.handle(EchoService)
+        t = Thread.new { @srv.run }
+        @srv.wait_till_running
+        blk = proc do
+          stub = EchoStub.new(@host, :this_channel_is_insecure, **client_opts)
+          requests = [EchoMsg.new, EchoMsg.new]
+          stub.a_client_streaming_rpc_unimplemented(requests)
+        end
+
+        begin
+          expect(&blk).to raise_error do |error|
+            expect(error).to be_a(GRPC::BadStatus)
+            expect(error.code).to eq(GRPC::Core::StatusCodes::UNIMPLEMENTED)
+          end
+        ensure
+          @srv.stop # should be call not to crash
+          t.join
+        end
+      end
+
       it 'should handle multiple sequential requests', server: true do
         @srv.handle(EchoService)
         t = Thread.new { @srv.run }
diff --git a/src/ruby/spec/support/services.rb b/src/ruby/spec/support/services.rb
index 6e693f1cdec..438459dfd79 100644
--- a/src/ruby/spec/support/services.rb
+++ b/src/ruby/spec/support/services.rb
@@ -33,6 +33,7 @@ class EchoService
   rpc :a_client_streaming_rpc, stream(EchoMsg), EchoMsg
   rpc :a_server_streaming_rpc, EchoMsg, stream(EchoMsg)
   rpc :a_bidi_rpc, stream(EchoMsg), stream(EchoMsg)
+  rpc :a_client_streaming_rpc_unimplemented, stream(EchoMsg), EchoMsg
   attr_reader :received_md
 
   def initialize(**kw)
diff --git a/test/core/gpr/BUILD b/test/core/gpr/BUILD
index d58d4f2a14d..67657ee1ce9 100644
--- a/test/core/gpr/BUILD
+++ b/test/core/gpr/BUILD
@@ -81,12 +81,12 @@ grpc_cc_test(
 grpc_cc_test(
     name = "mpscq_test",
     srcs = ["mpscq_test.cc"],
+    exec_compatible_with = ["//third_party/toolchains/machine_size:large"],
     language = "C++",
     deps = [
         "//:gpr",
         "//test/core/util:gpr_test_util",
     ],
-    data = ["//third_party/toolchains:RBE_USE_MACHINE_TYPE_LARGE"],
 )
 
 grpc_cc_test(
diff --git a/test/core/gprpp/inlined_vector_test.cc b/test/core/gprpp/inlined_vector_test.cc
index 73e0773b31d..6abd2e7dfaf 100644
--- a/test/core/gprpp/inlined_vector_test.cc
+++ b/test/core/gprpp/inlined_vector_test.cc
@@ -116,7 +116,7 @@ typedef InlinedVector<int, kInlinedLength> IntVec8;
 const size_t kInlinedFillSize = kInlinedLength - 1;
 const size_t kAllocatedFillSize = kInlinedLength + 1;
 
-TEST(InlinedVectorTest, CopyConstructerInlined) {
+TEST(InlinedVectorTest, CopyConstructorInlined) {
   IntVec8 original;
   FillVector(&original, kInlinedFillSize);
   IntVec8 copy_constructed(original);
@@ -125,7 +125,7 @@ TEST(InlinedVectorTest, CopyConstructerInlined) {
   }
 }
 
-TEST(InlinedVectorTest, CopyConstructerAllocated) {
+TEST(InlinedVectorTest, CopyConstructorAllocated) {
   IntVec8 original;
   FillVector(&original, kAllocatedFillSize);
   IntVec8 copy_constructed(original);
@@ -264,6 +264,166 @@ TEST(InlinedVectorTest, MoveAssignmentAllocatedAllocated) {
   EXPECT_EQ(move_assigned.data(), old_data);
 }
 
+// A copyable and movable value class, used to test that elements' copy
+// and move methods are called correctly.
+class Value {
+ public:
+  explicit Value(int v) : value_(MakeUnique<int>(v)) {}
+
+  // copyable
+  Value(const Value& v) {
+    value_ = MakeUnique<int>(*v.value_);
+    copied_ = true;
+  }
+  Value& operator=(const Value& v) {
+    value_ = MakeUnique<int>(*v.value_);
+    copied_ = true;
+    return *this;
+  }
+
+  // movable
+  Value(Value&& v) {
+    value_ = std::move(v.value_);
+    moved_ = true;
+  }
+  Value& operator=(Value&& v) {
+    value_ = std::move(v.value_);
+    moved_ = true;
+    return *this;
+  }
+
+  const UniquePtr<int>& value() const { return value_; }
+  bool copied() const { return copied_; }
+  bool moved() const { return moved_; }
+
+ private:
+  UniquePtr<int> value_;
+  bool copied_ = false;
+  bool moved_ = false;
+};
+
+TEST(InlinedVectorTest, CopyConstructorCopiesElementsInlined) {
+  InlinedVector<Value, 1> v1;
+  v1.emplace_back(3);
+  InlinedVector<Value, 1> v2(v1);
+  EXPECT_EQ(v2.size(), 1UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  // Addresses should differ.
+  EXPECT_NE(v1[0].value().get(), v2[0].value().get());
+  EXPECT_TRUE(v2[0].copied());
+}
+
+TEST(InlinedVectorTest, CopyConstructorCopiesElementsAllocated) {
+  InlinedVector<Value, 1> v1;
+  v1.reserve(2);
+  v1.emplace_back(3);
+  v1.emplace_back(5);
+  InlinedVector<Value, 1> v2(v1);
+  EXPECT_EQ(v2.size(), 2UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  EXPECT_EQ(*v2[1].value(), 5);
+  // Addresses should differ.
+  EXPECT_NE(v1[0].value().get(), v2[0].value().get());
+  EXPECT_NE(v1[1].value().get(), v2[1].value().get());
+  EXPECT_TRUE(v2[0].copied());
+  EXPECT_TRUE(v2[1].copied());
+}
+
+TEST(InlinedVectorTest, CopyAssignmentCopiesElementsInlined) {
+  InlinedVector<Value, 1> v1;
+  v1.emplace_back(3);
+  InlinedVector<Value, 1> v2;
+  EXPECT_EQ(v2.size(), 0UL);
+  v2 = v1;
+  EXPECT_EQ(v2.size(), 1UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  // Addresses should differ.
+  EXPECT_NE(v1[0].value().get(), v2[0].value().get());
+  EXPECT_TRUE(v2[0].copied());
+}
+
+TEST(InlinedVectorTest, CopyAssignmentCopiesElementsAllocated) {
+  InlinedVector<Value, 1> v1;
+  v1.reserve(2);
+  v1.emplace_back(3);
+  v1.emplace_back(5);
+  InlinedVector<Value, 1> v2;
+  EXPECT_EQ(v2.size(), 0UL);
+  v2 = v1;
+  EXPECT_EQ(v2.size(), 2UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  EXPECT_EQ(*v2[1].value(), 5);
+  // Addresses should differ.
+  EXPECT_NE(v1[0].value().get(), v2[0].value().get());
+  EXPECT_NE(v1[1].value().get(), v2[1].value().get());
+  EXPECT_TRUE(v2[0].copied());
+  EXPECT_TRUE(v2[1].copied());
+}
+
+TEST(InlinedVectorTest, MoveConstructorMovesElementsInlined) {
+  InlinedVector<Value, 1> v1;
+  v1.emplace_back(3);
+  int* addr = v1[0].value().get();
+  InlinedVector<Value, 1> v2(std::move(v1));
+  EXPECT_EQ(v2.size(), 1UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  EXPECT_EQ(addr, v2[0].value().get());
+  EXPECT_TRUE(v2[0].moved());
+}
+
+TEST(InlinedVectorTest, MoveConstructorMovesElementsAllocated) {
+  InlinedVector<Value, 1> v1;
+  v1.reserve(2);
+  v1.emplace_back(3);
+  v1.emplace_back(5);
+  int* addr1 = v1[0].value().get();
+  int* addr2 = v1[1].value().get();
+  Value* data1 = v1.data();
+  InlinedVector<Value, 1> v2(std::move(v1));
+  EXPECT_EQ(v2.size(), 2UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  EXPECT_EQ(*v2[1].value(), 5);
+  EXPECT_EQ(addr1, v2[0].value().get());
+  EXPECT_EQ(addr2, v2[1].value().get());
+  // In this case, elements won't be moved, because we have just stolen
+  // the underlying storage.
+  EXPECT_EQ(data1, v2.data());
+}
+
+TEST(InlinedVectorTest, MoveAssignmentMovesElementsInlined) {
+  InlinedVector<Value, 1> v1;
+  v1.emplace_back(3);
+  int* addr = v1[0].value().get();
+  InlinedVector<Value, 1> v2;
+  EXPECT_EQ(v2.size(), 0UL);
+  v2 = std::move(v1);
+  EXPECT_EQ(v2.size(), 1UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  EXPECT_EQ(addr, v2[0].value().get());
+  EXPECT_TRUE(v2[0].moved());
+}
+
+TEST(InlinedVectorTest, MoveAssignmentMovesElementsAllocated) {
+  InlinedVector<Value, 1> v1;
+  v1.reserve(2);
+  v1.emplace_back(3);
+  v1.emplace_back(5);
+  int* addr1 = v1[0].value().get();
+  int* addr2 = v1[1].value().get();
+  Value* data1 = v1.data();
+  InlinedVector<Value, 1> v2;
+  EXPECT_EQ(v2.size(), 0UL);
+  v2 = std::move(v1);
+  EXPECT_EQ(v2.size(), 2UL);
+  EXPECT_EQ(*v2[0].value(), 3);
+  EXPECT_EQ(*v2[1].value(), 5);
+  EXPECT_EQ(addr1, v2[0].value().get());
+  EXPECT_EQ(addr2, v2[1].value().get());
+  // In this case, elements won't be moved, because we have just stolen
+  // the underlying storage.
+  EXPECT_EQ(data1, v2.data());
+}
+
 TEST(InlinedVectorTest, PopBackInlined) {
   InlinedVector<UniquePtr<int>, 2> v;
   // Add two elements, pop one out
diff --git a/test/core/iomgr/BUILD b/test/core/iomgr/BUILD
index 70ee83acd23..e278632e502 100644
--- a/test/core/iomgr/BUILD
+++ b/test/core/iomgr/BUILD
@@ -40,7 +40,7 @@ grpc_cc_library(
 grpc_cc_test(
     name = "combiner_test",
     srcs = ["combiner_test.cc"],
-    data = ["//third_party/toolchains:RBE_USE_MACHINE_TYPE_LARGE"],
+    exec_compatible_with = ["//third_party/toolchains/machine_size:large"],
     language = "C++",
     deps = [
         "//:gpr",
diff --git a/test/cpp/end2end/grpclb_end2end_test.cc b/test/cpp/end2end/grpclb_end2end_test.cc
index 6ce0696114e..5b304dc16b1 100644
--- a/test/cpp/end2end/grpclb_end2end_test.cc
+++ b/test/cpp/end2end/grpclb_end2end_test.cc
@@ -553,10 +553,11 @@ class GrpclbEnd2endTest : public ::testing::Test {
     return status;
   }
 
-  void CheckRpcSendOk(const size_t times = 1, const int timeout_ms = 1000) {
+  void CheckRpcSendOk(const size_t times = 1, const int timeout_ms = 1000,
+                      bool wait_for_ready = false) {
     for (size_t i = 0; i < times; ++i) {
       EchoResponse response;
-      const Status status = SendRpc(&response, timeout_ms);
+      const Status status = SendRpc(&response, timeout_ms, wait_for_ready);
       EXPECT_TRUE(status.ok()) << "code=" << status.error_code()
                                << " message=" << status.error_message();
       EXPECT_EQ(response.message(), kRequestMessage_);
@@ -717,10 +718,9 @@ TEST_F(SingleBalancerTest, InitiallyEmptyServerlist) {
   ScheduleResponseForBalancer(
       0, BalancerServiceImpl::BuildResponseForBackends(GetBackendPorts(), {}),
       kServerlistDelayMs);
-
   const auto t0 = system_clock::now();
   // Client will block: LB will initially send empty serverlist.
-  CheckRpcSendOk(1, kCallDeadlineMs);
+  CheckRpcSendOk(1, kCallDeadlineMs, true /* wait_for_ready */);
   const auto ellapsed_ms =
       std::chrono::duration_cast<std::chrono::milliseconds>(
           system_clock::now() - t0);
diff --git a/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc b/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
index 85767c8758f..dca97c85b19 100644
--- a/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
+++ b/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
@@ -94,6 +94,7 @@ static const grpc_event_engine_vtable* init_engine_vtable(bool) {
   g_vtable.pollset_destroy = pollset_destroy;
   g_vtable.pollset_work = pollset_work;
   g_vtable.pollset_kick = pollset_kick;
+  g_vtable.shutdown_background_closure = [] {};
   g_vtable.shutdown_engine = [] {};
 
   return &g_vtable;
diff --git a/test/cpp/qps/BUILD b/test/cpp/qps/BUILD
index 26f43284a68..626ac5f3f2e 100644
--- a/test/cpp/qps/BUILD
+++ b/test/cpp/qps/BUILD
@@ -170,7 +170,7 @@ grpc_cc_test(
 grpc_cc_test(
     name = "qps_openloop_test",
     srcs = ["qps_openloop_test.cc"],
-    data = ["//third_party/toolchains:RBE_USE_MACHINE_TYPE_LARGE"],
+    exec_compatible_with = ["//third_party/toolchains/machine_size:large"],
     deps = [
         ":benchmark_config",
         ":driver_impl",
diff --git a/third_party/toolchains/BUILD b/third_party/toolchains/BUILD
index 02cd87a7b9b..e213461acc9 100644
--- a/third_party/toolchains/BUILD
+++ b/third_party/toolchains/BUILD
@@ -16,37 +16,72 @@ licenses(["notice"])  # Apache v2
 
 package(default_visibility = ["//visibility:public"])
 
-exports_files(["RBE_USE_MACHINE_TYPE_LARGE",])
-
 # Latest RBE Ubuntu16_04 container
 # Update every time when a new container is released.
 alias(
     name = "rbe_ubuntu1604",
-    actual = ":rbe_ubuntu1604_r328903",
+    actual = ":rbe_ubuntu1604_r342117",
+)
+
+alias(
+    name = "rbe_ubuntu1604_large",
+    actual = ":rbe_ubuntu1604_r342117_large",
 )
 
-# RBE Ubuntu16_04 r328903
+# RBE Ubuntu16_04 r342117
 platform(
-    name = "rbe_ubuntu1604_r328903",
+    name = "rbe_ubuntu1604_r342117",
     constraint_values = [
         "@bazel_tools//platforms:x86_64",
         "@bazel_tools//platforms:linux",
         "@bazel_tools//tools/cpp:clang",
         "@com_github_bazelbuild_bazeltoolchains//constraints:xenial",
         "@com_github_bazelbuild_bazeltoolchains//constraints/sanitizers:support_msan",
+        "//third_party/toolchains/machine_size:standard",
     ],
     remote_execution_properties = """
         properties: {
           name: "container-image"
-          value:"docker://gcr.io/cloud-marketplace/google/rbe-ubuntu16-04@sha256:59bf0e191a6b5cc1ab62c2224c810681d1326bad5a27b1d36c9f40113e79da7f"
+          value:"docker://gcr.io/cloud-marketplace/google/rbe-ubuntu16-04@sha256:f3120a030a19d67626ababdac79cc787e699a1aa924081431285118f87e7b375"
         }
         properties: {
           name: "gceMachineType"  # Small machines for majority of tests.
           value: "n1-highmem-2"
         }
+        """,
+)
+
+# RBE Ubuntu16_04 r342117 large
+platform(
+    name = "rbe_ubuntu1604_r342117_large",
+    constraint_values = [
+        "@bazel_tools//platforms:x86_64",
+        "@bazel_tools//platforms:linux",
+        "@bazel_tools//tools/cpp:clang",
+        "@com_github_bazelbuild_bazeltoolchains//constraints:xenial",
+        "@com_github_bazelbuild_bazeltoolchains//constraints/sanitizers:support_msan",
+        "//third_party/toolchains/machine_size:large",
+    ],
+    remote_execution_properties = """
+        properties: {
+          name: "container-image"
+          value:"docker://gcr.io/cloud-marketplace/google/rbe-ubuntu16-04@sha256:f3120a030a19d67626ababdac79cc787e699a1aa924081431285118f87e7b375"
+        }
         properties: {
-          name: "gceMachineType_LARGE"  # Large machines for a small set of resource-consuming tests such as combiner_tests under TSAN.
+          name: "gceMachineType"  # Large machines for some resource demanding tests (TSAN).
           value: "n1-standard-8"
         }
-        """,
+    """,
+)
+
+# This target is auto-generated from release/cpp.tpl and should not be
+# modified directly.
+toolchain(
+    name = "cc-toolchain-clang-x86_64-default",
+    exec_compatible_with = [
+    ],
+    target_compatible_with = [
+    ],
+    toolchain = "@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.1/bazel_0.16.1/default:cc-compiler-k8",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
 )
diff --git a/third_party/toolchains/RBE_USE_MACHINE_TYPE_LARGE b/third_party/toolchains/RBE_USE_MACHINE_TYPE_LARGE
deleted file mode 100644
index b1120238d7e..00000000000
--- a/third_party/toolchains/RBE_USE_MACHINE_TYPE_LARGE
+++ /dev/null
@@ -1 +0,0 @@
-# This file is a sentinel and is meant to be empty.
diff --git a/third_party/toolchains/machine_size/BUILD b/third_party/toolchains/machine_size/BUILD
new file mode 100644
index 00000000000..cc962946c31
--- /dev/null
+++ b/third_party/toolchains/machine_size/BUILD
@@ -0,0 +1,31 @@
+# Copyright 2018 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+licenses(["notice"])  # Apache v2
+
+package(default_visibility = ["//visibility:public"])
+
+constraint_setting(name = "machine_size")
+
+constraint_value(
+    name = "large",
+    constraint_setting = ":machine_size",
+)
+
+constraint_value(
+    name = "standard",
+    constraint_setting = ":machine_size",
+)
+
+# Add other constraint values as needed (tiny, huge, etc.) in the future.
diff --git a/third_party/upb b/third_party/upb
new file mode 160000
index 00000000000..9ce4a77f61c
--- /dev/null
+++ b/third_party/upb
@@ -0,0 +1 @@
+Subproject commit 9ce4a77f61c134bbed28bfd5be5cd7dc0e80f5e3
diff --git a/tools/doxygen/Doxyfile.c++ b/tools/doxygen/Doxyfile.c++
index fbac37e8e75..5c19711ee91 100644
--- a/tools/doxygen/Doxyfile.c++
+++ b/tools/doxygen/Doxyfile.c++
@@ -777,6 +777,7 @@ doc/environment_variables.md \
 doc/fail_fast.md \
 doc/fork_support.md \
 doc/g_stands_for.md \
+doc/grpc_release_schedule.md \
 doc/health-checking.md \
 doc/http-grpc-status-mapping.md \
 doc/http2-interop-test-descriptions.md \
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index f7a9c79620b..72b247c48da 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -777,6 +777,7 @@ doc/environment_variables.md \
 doc/fail_fast.md \
 doc/fork_support.md \
 doc/g_stands_for.md \
+doc/grpc_release_schedule.md \
 doc/health-checking.md \
 doc/http-grpc-status-mapping.md \
 doc/http2-interop-test-descriptions.md \
diff --git a/tools/doxygen/Doxyfile.core b/tools/doxygen/Doxyfile.core
index b78fb607ad3..8c557383b2e 100644
--- a/tools/doxygen/Doxyfile.core
+++ b/tools/doxygen/Doxyfile.core
@@ -784,6 +784,7 @@ doc/environment_variables.md \
 doc/fail_fast.md \
 doc/fork_support.md \
 doc/g_stands_for.md \
+doc/grpc_release_schedule.md \
 doc/health-checking.md \
 doc/http-grpc-status-mapping.md \
 doc/http2-interop-test-descriptions.md \
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index b4f15886c66..0f1943de25f 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -784,6 +784,7 @@ doc/environment_variables.md \
 doc/fail_fast.md \
 doc/fork_support.md \
 doc/g_stands_for.md \
+doc/grpc_release_schedule.md \
 doc/health-checking.md \
 doc/http-grpc-status-mapping.md \
 doc/http2-interop-test-descriptions.md \
diff --git a/tools/remote_build/rbe_common.bazelrc b/tools/remote_build/rbe_common.bazelrc
index 75a42a317e8..aa3ddb050cd 100644
--- a/tools/remote_build/rbe_common.bazelrc
+++ b/tools/remote_build/rbe_common.bazelrc
@@ -18,10 +18,10 @@
 
 startup --host_jvm_args=-Dbazel.DigestFunction=SHA256
 
-build --crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.0/bazel_0.16.1/default:toolchain
-build --extra_toolchains=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.0/bazel_0.16.1/cpp:cc-toolchain-clang-x86_64-default
+build --crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.1/bazel_0.16.1/default:toolchain
+build --extra_toolchains=//third_party/toolchains:cc-toolchain-clang-x86_64-default
 # Use custom execution platforms defined in third_party/toolchains
-build --extra_execution_platforms=//third_party/toolchains:rbe_ubuntu1604
+build --extra_execution_platforms=//third_party/toolchains:rbe_ubuntu1604,//third_party/toolchains:rbe_ubuntu1604_large
 build --host_platform=//third_party/toolchains:rbe_ubuntu1604
 build --platforms=//third_party/toolchains:rbe_ubuntu1604
 
@@ -61,9 +61,9 @@ build:msan --cxxopt=--stdlib=libc++
 # setting LD_LIBRARY_PATH is necessary
 # to avoid "libc++.so.1: cannot open shared object file"
 build:msan --action_env=LD_LIBRARY_PATH=/usr/local/lib
-build:msan --host_crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.0/bazel_0.16.1/default:toolchain
+build:msan --host_crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.1/bazel_0.16.1/default:toolchain
 # override the config-agnostic crosstool_top
-build:msan --crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.0/bazel_0.16.1/msan:toolchain
+build:msan --crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/ubuntu16_04_clang/1.1/bazel_0.16.1/msan:toolchain
 
 # thread sanitizer: most settings are already in %workspace%/.bazelrc
 # we only need a few additional ones that are Foundry specific
@@ -71,6 +71,7 @@ build:tsan --copt=-gmlt
 # TODO(jtattermusch): use more reasonable test timeout
 build:tsan --test_timeout=3600
 build:tsan --test_tag_filters=-qps_json_driver
+build:tsan --extra_execution_platforms=//third_party/toolchains:rbe_ubuntu1604,//third_party/toolchains:rbe_ubuntu1604_large
 
 # undefined behavior sanitizer: most settings are already in %workspace%/.bazelrc
 # we only need a few additional ones that are Foundry specific
@@ -78,7 +79,7 @@ build:ubsan --copt=-gmlt
 # TODO(jtattermusch): use more reasonable test timeout
 build:ubsan --test_timeout=3600
 # override the config-agnostic crosstool_top
---crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/experimental/ubuntu16_04_clang/1.0/bazel_0.16.1/ubsan:toolchain
+--crosstool_top=@com_github_bazelbuild_bazeltoolchains//configs/experimental/ubuntu16_04_clang/1.1/bazel_0.16.1/ubsan:toolchain
 # TODO(jtattermusch): remove this once Foundry adds the env to the docker image.
 # ubsan needs symbolizer to work properly, otherwise the suppression file doesn't work
 # and we get test failures.
diff --git a/tools/run_tests/sanity/check_bazel_workspace.py b/tools/run_tests/sanity/check_bazel_workspace.py
index d562fffc8a9..35da88d70e6 100755
--- a/tools/run_tests/sanity/check_bazel_workspace.py
+++ b/tools/run_tests/sanity/check_bazel_workspace.py
@@ -42,6 +42,7 @@ _ZOPEFOUNDATION_ZOPE_INTERFACE_DEP_NAME = 'com_github_zopefoundation_zope_interf
 _TWISTED_CONSTANTLY_DEP_NAME = 'com_github_twisted_constantly'
 
 _GRPC_DEP_NAMES = [
+    'upb',
     'boringssl',
     'com_github_madler_zlib',
     'com_google_protobuf',
diff --git a/tools/run_tests/sanity/check_submodules.sh b/tools/run_tests/sanity/check_submodules.sh
index fa2628f18ea..f1103596d51 100755
--- a/tools/run_tests/sanity/check_submodules.sh
+++ b/tools/run_tests/sanity/check_submodules.sh
@@ -40,6 +40,7 @@ cat << EOF | awk '{ print $1 }' | sort > "$want_submodules"
  9245d481eb3e890f708ff2d7dadf2a10c04748ba third_party/libcxxabi (heads/release_60)
  48cb18e5c419ddd23d9badcfe4e9df7bde1979b2 third_party/protobuf (v3.6.0.1-37-g48cb18e5)
  e143189bf6f37b3957fb31743df6a1bcf4a8c685 third_party/protoc-gen-validate (v0.0.10)
+ 9ce4a77f61c134bbed28bfd5be5cd7dc0e80f5e3 third_party/upb (heads/upbc-cpp)
  cacf7f1d4e3d44d871b605da3b647f07d718623f third_party/zlib (v1.2.11)
 EOF