diff --git a/lib/mongo/server/monitor.rb b/lib/mongo/server/monitor.rb
index 572484ed15..75f3d51e79 100644
--- a/lib/mongo/server/monitor.rb
+++ b/lib/mongo/server/monitor.rb
@@ -210,28 +210,41 @@ def scan!
         @mutex.synchronize do
           throttle_scan_frequency!
 
+          # When the streaming protocol is active the PushMonitor is the
+          # authoritative SDAM source and this scan only measures RTT on the
+          # dedicated connection. Per the Server Monitoring spec, an RTT
+          # command MUST NOT publish events or update the topology. Compute
+          # this before do_scan, which may (re)connect and change the state.
+          rtt_only = rtt_measurement_only?
+
           begin
-            result = do_scan
+            result = do_scan(publish_heartbeat: !rtt_only)
           rescue StandardError => e
-            run_sdam_flow({}, scan_error: e)
+            run_sdam_flow({}, scan_error: e, rtt_only: rtt_only)
           else
-            run_sdam_flow(result)
+            run_sdam_flow(result, rtt_only: rtt_only)
           end
         end
       end
 
-      def run_sdam_flow(result, awaited: false, scan_error: nil)
+      def run_sdam_flow(result, awaited: false, scan_error: nil, rtt_only: false)
         @sdam_mutex.synchronize do
           old_description = server.description
 
-          new_description = Description.new(
-            server.address,
-            result,
-            average_round_trip_time: server.round_trip_time_calculator.average_round_trip_time,
-            minimum_round_trip_time: server.round_trip_time_calculator.minimum_round_trip_time
-          )
-
-          server.cluster.run_sdam_flow(server.description, new_description, awaited: awaited, scan_error: scan_error)
+          # An RTT-only measurement (streaming protocol active) must not update
+          # the topology or publish SDAM events. The RTT it gathered is
+          # incorporated into the next streaming-hello description via the
+          # shared RTT calculator. The scheduling below still runs so the
+          # monitor keeps pacing its checks.
+          unless rtt_only
+            new_description = Description.new(
+              server.address,
+              result,
+              average_round_trip_time: server.round_trip_time_calculator.average_round_trip_time,
+              minimum_round_trip_time: server.round_trip_time_calculator.minimum_round_trip_time
+            )
+            server.cluster.run_sdam_flow(server.description, new_description, awaited: awaited, scan_error: scan_error)
+          end
 
           server.description.tap do |new_description|
             unless awaited
@@ -272,8 +285,12 @@ def pre_stop
         server.scan_semaphore.signal
       end
 
-      def do_scan
-        monitoring.publish_heartbeat(server) do
+      def do_scan(publish_heartbeat: true)
+        if publish_heartbeat
+          monitoring.publish_heartbeat(server) do
+            check
+          end
+        else
           check
         end
       rescue StandardError => e
@@ -285,6 +302,28 @@ def do_scan
         raise e
       end
 
+      # Returns whether this scan is only an RTT measurement, which is the case
+      # when the streaming protocol is active: a dedicated connection is already
+      # established and the PushMonitor is running as the authoritative SDAM
+      # source. In the polling protocol there is no running PushMonitor, so the
+      # connection-reuse check is a real server check and not RTT-only.
+      #
+      # @return [ true | false ]
+      def rtt_measurement_only?
+        return false if @connection.nil?
+
+        # Only suppress the check while the server is in a known state and the
+        # PushMonitor is the authoritative streaming source. If the server is
+        # Unknown (e.g. an operation error or a streaming failure just marked
+        # it so), the polling Monitor must run a full check to recover it
+        # rather than waiting for the next streaming response - otherwise the
+        # server can stay Unknown long enough to fail server selection.
+        return false if server.unknown?
+
+        pm = push_monitor
+        !pm.nil? && pm.running?
+      end
+
       def check
         if @connection && @connection.pid != Process.pid
           log_warn("Detected PID change - Mongo client should have been reconnected (old pid #{@connection.pid}, new pid #{Process.pid}")
diff --git a/lib/mongo/server/push_monitor.rb b/lib/mongo/server/push_monitor.rb
index 280565416f..a2db56504a 100644
--- a/lib/mongo/server/push_monitor.rb
+++ b/lib/mongo/server/push_monitor.rb
@@ -118,6 +118,13 @@ def do_work
                                 log_prefix: options[:log_prefix],
                                 bg_error_backtrace: options[:bg_error_backtrace])
 
+        # The streaming check is the authoritative SDAM source, so its failure
+        # must mark the server Unknown and clear the pool here. While streaming
+        # is active the polling Monitor only measures RTT and ignores errors
+        # (per the Server Monitoring spec), so it can no longer be relied on to
+        # notice the failure.
+        monitor.run_sdam_flow({}, scan_error: e, awaited: true)
+
         # If a request failed on a connection, stop push monitoring.
         # In case the server is dead we don't want to have two connections
         # trying to connect unsuccessfully at the same time.
@@ -142,6 +149,13 @@ def check
             @server_pushing = false
             connection = PushMonitor::Connection.new(server.address, options)
             connection.connect!
+            # Identify the streaming connection to the server with a metadata
+            # handshake (carrying the appName) before streaming, mirroring the
+            # polling Monitor and the Server Monitoring spec, which establishes
+            # the monitoring connection with a handshake before issuing the
+            # awaitable hello. Without this, appName-scoped server behaviour
+            # never applies to the streaming hello.
+            connection.handshake!
             @connection = connection
           end
         end
diff --git a/spec/mongo/server/monitor_spec.rb b/spec/mongo/server/monitor_spec.rb
index 2978ae3bff..562085bcae 100644
--- a/spec/mongo/server/monitor_spec.rb
+++ b/spec/mongo/server/monitor_spec.rb
@@ -122,6 +122,151 @@
         end
       end
     end
+
+    context 'when streaming is active and the scan is an RTT-only measurement' do
+      # Steady-state streaming: the Monitor already has an established
+      # connection (used only for RTT measurement) and a running PushMonitor
+      # that is the authoritative SDAM source. Per the Server Monitoring spec
+      # ("Measuring RTT" / "SDAM Monitoring"), clients MUST NOT publish any
+      # events and MUST NOT update the topology when running an RTT command.
+
+      let(:hello_reply) do
+        {
+          'isWritablePrimary' => true,
+          'ok' => 1.0,
+          'minWireVersion' => 0,
+          'maxWireVersion' => 21,
+        }
+      end
+
+      let(:rtt_connection) do
+        double('monitor connection').tap do |conn|
+          allow(conn).to receive(:pid).and_return(Process.pid)
+          allow(conn).to receive(:check_document).and_return({ 'hello' => 1 })
+          allow(conn).to receive(:dispatch_bytes).and_return(
+            double('message', documents: [ hello_reply ])
+          )
+          allow(conn).to receive(:disconnect!)
+        end
+      end
+
+      let(:running_push_monitor) do
+        double('push monitor').tap do |push_monitor|
+          allow(push_monitor).to receive(:running?).and_return(true)
+          allow(push_monitor).to receive(:stop!)
+        end
+      end
+
+      before do
+        # The server must be in a known state for RTT-only suppression to
+        # apply; an Unknown server is always given a full recovery check.
+        server.update_description(Mongo::Server::Description.new(address, hello_reply))
+        expect(server.description).not_to be_unknown
+        monitor.instance_variable_set(:@connection, rtt_connection)
+        monitor.instance_variable_set(:@push_monitor, running_push_monitor)
+      end
+
+      it 'does not run the SDAM flow' do
+        expect(cluster).not_to receive(:run_sdam_flow)
+        monitor.scan!
+      end
+
+      it 'does not publish heartbeat events' do
+        expect(monitor.monitoring).not_to receive(:publish_heartbeat)
+        monitor.scan!
+      end
+    end
+
+    context 'when streaming is active but the server is Unknown' do
+      # Recovery path: even with an established connection and a running
+      # PushMonitor, an Unknown server must get a full check so it is
+      # recovered promptly, rather than waiting for the next streaming
+      # response (which could be up to heartbeatFrequencyMS away and would
+      # let server selection fail in the meantime).
+
+      let(:hello_reply) do
+        {
+          'isWritablePrimary' => true,
+          'ok' => 1.0,
+          'minWireVersion' => 0,
+          'maxWireVersion' => 21,
+        }
+      end
+
+      let(:rtt_connection) do
+        double('monitor connection').tap do |conn|
+          allow(conn).to receive(:pid).and_return(Process.pid)
+          allow(conn).to receive(:check_document).and_return({ 'hello' => 1 })
+          allow(conn).to receive(:dispatch_bytes).and_return(
+            double('message', documents: [ hello_reply ])
+          )
+          allow(conn).to receive(:disconnect!)
+        end
+      end
+
+      let(:running_push_monitor) do
+        double('push monitor').tap do |push_monitor|
+          allow(push_monitor).to receive(:running?).and_return(true)
+          allow(push_monitor).to receive(:stop!)
+        end
+      end
+
+      before do
+        # Server starts Unknown (monitoring_io is disabled).
+        expect(server.description).to be_unknown
+        monitor.instance_variable_set(:@connection, rtt_connection)
+        monitor.instance_variable_set(:@push_monitor, running_push_monitor)
+      end
+
+      it 'runs the SDAM flow to recover the server' do
+        expect(cluster).to receive(:run_sdam_flow)
+        monitor.scan!
+      end
+    end
+
+    context 'when in the polling protocol with an established connection' do
+      # Polling protocol (serverMonitoringMode=poll, FaaS, or pre-4.4): there
+      # is no PushMonitor, so reusing the connection to run hello is a real
+      # server check, not an RTT-only measurement. It must keep publishing
+      # events and running the SDAM flow exactly as before. This guards
+      # against the RTT-only suppression leaking into polling mode.
+
+      let(:hello_reply) do
+        {
+          'isWritablePrimary' => true,
+          'ok' => 1.0,
+          'minWireVersion' => 0,
+          'maxWireVersion' => 21,
+        }
+      end
+
+      let(:polling_connection) do
+        double('monitor connection').tap do |conn|
+          allow(conn).to receive(:pid).and_return(Process.pid)
+          allow(conn).to receive(:check_document).and_return({ 'hello' => 1 })
+          allow(conn).to receive(:dispatch_bytes).and_return(
+            double('message', documents: [ hello_reply ])
+          )
+          allow(conn).to receive(:disconnect!)
+        end
+      end
+
+      before do
+        monitor.instance_variable_set(:@connection, polling_connection)
+        # No PushMonitor exists in polling mode.
+        expect(monitor.push_monitor).to be_nil
+      end
+
+      it 'runs the SDAM flow' do
+        expect(cluster).to receive(:run_sdam_flow)
+        monitor.scan!
+      end
+
+      it 'publishes heartbeat events' do
+        expect(monitor.monitoring).to receive(:publish_heartbeat).and_call_original
+        monitor.scan!
+      end
+    end
   end
 
   # heartbeat interval is now taken out of cluster, monitor has no useful options
diff --git a/spec/mongo/server/push_monitor_spec.rb b/spec/mongo/server/push_monitor_spec.rb
index cab0d41065..56a15fd231 100644
--- a/spec/mongo/server/push_monitor_spec.rb
+++ b/spec/mongo/server/push_monitor_spec.rb
@@ -67,6 +67,19 @@
       end.should_not raise_error
     end
 
+    # The streaming connection must identify itself to the server with a
+    # metadata handshake (carrying the appName) before streaming, like the
+    # polling Monitor's connection does. Otherwise appName-scoped server
+    # behaviour (e.g. failCommand fail points used by the SDAM spec tests)
+    # never applies to the streaming hello, and the streaming check cannot
+    # observe monitor errors.
+    it 'performs a metadata handshake before streaming' do
+      expect_any_instance_of(Mongo::Server::PushMonitor::Connection)
+        .to receive(:handshake!).and_call_original
+
+      push_monitor.do_work
+    end
+
     context 'network error during check' do
       it 'does not propagate the exception' do
         push_monitor
@@ -89,6 +102,27 @@
 
         push_monitor.running?.should be false
       end
+
+      # Per the Server Monitoring spec ("Network or command error during server
+      # check"), the streaming monitor must mark the server Unknown and clear
+      # the pool when its check fails. In the Ruby driver the PushMonitor owns
+      # the streaming check, so it must run the SDAM flow with the scan error
+      # rather than relying on the polling Monitor to notice the failure.
+      it 'marks the server unknown via the SDAM flow' do
+        push_monitor
+
+        expect(Socket).to receive(:getaddrinfo).and_raise(SocketError.new('Test exception'))
+
+        expect(cluster).to receive(:run_sdam_flow) do |_previous_desc, updated_desc, options|
+          expect(updated_desc).to be_unknown
+          expect(options[:awaited]).to be true
+          expect(options[:scan_error]).to be_a(Mongo::Error::SocketError)
+        end
+
+        lambda do
+          push_monitor.do_work
+        end.should_not raise_error
+      end
     end
   end
 end
diff --git a/spec/spec_tests/data/sdam_unified/interruptInUse-pool-clear.yml b/spec/spec_tests/data/sdam_unified/interruptInUse-pool-clear.yml
index 9293a986d5..67cd7d3ae3 100644
--- a/spec/spec_tests/data/sdam_unified/interruptInUse-pool-clear.yml
+++ b/spec/spec_tests/data/sdam_unified/interruptInUse-pool-clear.yml
@@ -81,7 +81,7 @@ tests:
           failPoint:
             configureFailPoint: failCommand
             mode:
-              times: 1
+              times: 4
             data:
               failCommands:
                 - hello
@@ -182,7 +182,7 @@ tests:
           failPoint:
             configureFailPoint: failCommand
             mode:
-              times: 1
+              times: 4
             data:
               failCommands:
                 - hello
@@ -291,7 +291,7 @@ tests:
           failPoint:
             configureFailPoint: failCommand
             mode:
-              times: 1
+              times: 4
             data:
               failCommands:
                 - hello