diff --git a/mcrouter/lib/carbon/MessageCommon.h b/mcrouter/lib/carbon/MessageCommon.h
index 71193791..3d2fcd44 100644
--- a/mcrouter/lib/carbon/MessageCommon.h
+++ b/mcrouter/lib/carbon/MessageCommon.h
@@ -37,6 +37,9 @@ class MessageCommon {
   static constexpr std::string_view kCryptoAuthTokenHeader =
       "crypto_auth_tokens";
 
+  static constexpr std::string_view kClientIdentifierHeader =
+      "client_identifier";
+
  protected:
   std::string traceContext_;
 };
diff --git a/mcrouter/lib/carbon/RequestCommon.h b/mcrouter/lib/carbon/RequestCommon.h
index bcd1c196..b0761248 100644
--- a/mcrouter/lib/carbon/RequestCommon.h
+++ b/mcrouter/lib/carbon/RequestCommon.h
@@ -24,11 +24,13 @@ class RequestCommon : public MessageCommon {
   RequestCommon(const RequestCommon& other) {
     traceContext_ = other.traceContext_;
     cryptoAuthToken_ = other.cryptoAuthToken_;
+    clientIdentifier_ = other.clientIdentifier_;
   }
   RequestCommon& operator=(const RequestCommon& other) {
     if (this != &other) {
       traceContext_ = other.traceContext_;
       cryptoAuthToken_ = other.cryptoAuthToken_;
+      clientIdentifier_ = other.clientIdentifier_;
     }
     return *this;
   }
@@ -83,7 +85,7 @@ class RequestCommon : public MessageCommon {
     return cryptoAuthToken_;
   }
 
-  const std::string& getClientIdentifier() const noexcept {
+  const std::optional<std::string>& getClientIdentifier() const noexcept {
     return clientIdentifier_;
   }
 
@@ -101,7 +103,7 @@ class RequestCommon : public MessageCommon {
   // cat token(s) in string serialzed format
   std::optional<std::string> cryptoAuthToken_;
   // Hash string of primary (non-host) tls client identities
-  std::string clientIdentifier_;
+  std::optional<std::string> clientIdentifier_;
 };
 
 } // namespace carbon
diff --git a/mcrouter/lib/carbon/example/gen/HelloGoodbyeThriftTransport.h b/mcrouter/lib/carbon/example/gen/HelloGoodbyeThriftTransport.h
index 901bbffc..f1852024 100644
--- a/mcrouter/lib/carbon/example/gen/HelloGoodbyeThriftTransport.h
+++ b/mcrouter/lib/carbon/example/gen/HelloGoodbyeThriftTransport.h
@@ -50,6 +50,10 @@ folly::Try<apache::thrift::RpcResponseComplete<hellogoodbye::GoodbyeReply>> send
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -86,6 +90,10 @@ folly::Try<apache::thrift::RpcResponseComplete<hellogoodbye::HelloReply>> sendSy
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -125,6 +133,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McVersionReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
diff --git a/mcrouter/lib/carbon/example/main.cpp b/mcrouter/lib/carbon/example/main.cpp
index 49e337cc..449ae94a 100644
--- a/mcrouter/lib/carbon/example/main.cpp
+++ b/mcrouter/lib/carbon/example/main.cpp
@@ -82,6 +82,11 @@ class ThriftHandler : virtual public hellogoodbye::thrift::HelloGoodbyeSvIf {
         LOG(INFO) << "Got optional header props " << it->second
                   << " from thrift header.";
       }
+      it = headers.find("client_identifier");
+      if (it != headers.end()) {
+        LOG(INFO) << "Got client_identifier " << it->second
+                  << " from thrift header.";
+      }
     } else {
       LOG(ERROR) << "Cannot get context.";
     }
diff --git a/mcrouter/lib/carbon/test/gen/AThriftTransport.h b/mcrouter/lib/carbon/test/gen/AThriftTransport.h
index 16ff272f..95cb868f 100644
--- a/mcrouter/lib/carbon/test/gen/AThriftTransport.h
+++ b/mcrouter/lib/carbon/test/gen/AThriftTransport.h
@@ -50,6 +50,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::A::TestAReply>> sen
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -86,6 +90,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McVersionReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
diff --git a/mcrouter/lib/carbon/test/gen/BThriftTransport.h b/mcrouter/lib/carbon/test/gen/BThriftTransport.h
index 24662d10..16402451 100644
--- a/mcrouter/lib/carbon/test/gen/BThriftTransport.h
+++ b/mcrouter/lib/carbon/test/gen/BThriftTransport.h
@@ -50,6 +50,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::B::TestBReply>> sen
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -86,6 +90,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McVersionReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
diff --git a/mcrouter/lib/carbon/test/gen/CarbonTestThriftTransport.h b/mcrouter/lib/carbon/test/gen/CarbonTestThriftTransport.h
index 3f5836ac..40ae29a8 100644
--- a/mcrouter/lib/carbon/test/gen/CarbonTestThriftTransport.h
+++ b/mcrouter/lib/carbon/test/gen/CarbonTestThriftTransport.h
@@ -50,6 +50,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::TestReply>> sendSyn
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -86,6 +90,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::TestReplyStringKey>
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -122,6 +130,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McVersionReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
diff --git a/mcrouter/lib/carbon/test/gen/CarbonThriftTestThriftTransport.h b/mcrouter/lib/carbon/test/gen/CarbonThriftTestThriftTransport.h
index 3f634110..c563d75e 100644
--- a/mcrouter/lib/carbon/test/gen/CarbonThriftTestThriftTransport.h
+++ b/mcrouter/lib/carbon/test/gen/CarbonThriftTestThriftTransport.h
@@ -50,6 +50,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::CustomReply>> sendS
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -86,6 +90,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::DummyThriftReply>>
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -122,6 +130,10 @@ folly::Try<apache::thrift::RpcResponseComplete<carbon::test::ThriftTestReply>> s
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -158,6 +170,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McVersionReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
diff --git a/mcrouter/lib/network/gen/MemcacheThriftTransport.h b/mcrouter/lib/network/gen/MemcacheThriftTransport.h
index b94c3b63..fcc82d34 100644
--- a/mcrouter/lib/network/gen/MemcacheThriftTransport.h
+++ b/mcrouter/lib/network/gen/MemcacheThriftTransport.h
@@ -50,6 +50,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McAddReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -86,6 +90,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McAppendReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -122,6 +130,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McCasReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -158,6 +170,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McDecrReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -194,6 +210,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McDeleteReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -230,6 +250,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McFlushAllReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -266,6 +290,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McFlushReReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -302,6 +330,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McGatReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -338,6 +370,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McGatsReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -374,6 +410,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McGetReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -410,6 +450,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McGetsReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -446,6 +490,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McIncrReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -482,6 +530,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McLeaseGetReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -518,6 +570,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McLeaseSetReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -554,6 +610,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McMetagetReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -590,6 +650,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McPrependReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -626,6 +690,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McReplaceReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -662,6 +730,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McSetReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -698,6 +770,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McTouchReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE
@@ -734,6 +810,10 @@ folly::Try<apache::thrift::RpcResponseComplete<McVersionReply>> sendSyncHelper(
     rpcOptions.setWriteHeader(
         std::string{carbon::MessageCommon::kCryptoAuthTokenHeader}, request.getCryptoAuthToken().value());
   }
+  if (FOLLY_UNLIKELY(request.getClientIdentifier().has_value())) {
+    rpcOptions.setWriteHeader(
+        std::string{carbon::MessageCommon::kClientIdentifierHeader}, request.getClientIdentifier().value());
+  }
   rpcOptions.setContextPropMask(0);
 
 #ifndef LIBMC_FBTRACE_DISABLE