diff --git a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorRefSerializationSpec.scala b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorRefSerializationSpec.scala
index b01dc695af..99a448b530 100644
--- a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorRefSerializationSpec.scala
+++ b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorRefSerializationSpec.scala
@@ -5,7 +5,6 @@
 package akka.actor.typed.internal
 
 import akka.actor.typed.scaladsl.Behaviors
-import akka.actor.typed.scaladsl.adapter._
 import akka.actor.typed.ActorRef
 import akka.serialization.{ JavaSerializer, SerializationExtension }
 import akka.actor.testkit.typed.scaladsl.ScalaTestWithActorTestKit
@@ -32,7 +31,7 @@ class ActorRefSerializationSpec
     with WordSpecLike
     with LogCapturing {
 
-  val serialization = SerializationExtension(system.toClassic)
+  val serialization = SerializationExtension(system)
 
   "ActorRef[T]" must {
     "be serialized and deserialized by MiscMessageSerializer" in {
diff --git a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorSystemSpec.scala b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorSystemSpec.scala
index 9c42737e54..95e4427af0 100644
--- a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorSystemSpec.scala
+++ b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/ActorSystemSpec.scala
@@ -14,7 +14,6 @@ import akka.actor.{ Address, CoordinatedShutdown, InvalidMessageException }
 import akka.actor.testkit.typed.scaladsl.TestInbox
 import akka.actor.testkit.typed.scaladsl.LogCapturing
 import akka.actor.typed.scaladsl.Behaviors
-import akka.actor.typed.scaladsl.adapter._
 import org.scalatest._
 import org.scalatest.concurrent.Eventually
 import org.scalatest.concurrent.ScalaFutures
@@ -62,8 +61,7 @@ class ActorSystemSpec
         }
         inbox.receiveAll() should ===("hello" :: Nil)
         sys.whenTerminated.futureValue
-        CoordinatedShutdown(sys.toClassic).shutdownReason() should ===(
-          Some(CoordinatedShutdown.ActorSystemTerminateReason))
+        CoordinatedShutdown(sys).shutdownReason() should ===(Some(CoordinatedShutdown.ActorSystemTerminateReason))
       }
     }
 
@@ -98,8 +96,7 @@ class ActorSystemSpec
       // now we know that the guardian has started, and should receive PostStop
       sys.terminate()
       sys.whenTerminated.futureValue
-      CoordinatedShutdown(sys.toClassic).shutdownReason() should ===(
-        Some(CoordinatedShutdown.ActorSystemTerminateReason))
+      CoordinatedShutdown(sys).shutdownReason() should ===(Some(CoordinatedShutdown.ActorSystemTerminateReason))
       inbox.receiveAll() should ===("done" :: Nil)
     }
 
diff --git a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/receptionist/ServiceKeySerializationSpec.scala b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/receptionist/ServiceKeySerializationSpec.scala
index 5fd7908902..c78ccdd0ba 100644
--- a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/receptionist/ServiceKeySerializationSpec.scala
+++ b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/internal/receptionist/ServiceKeySerializationSpec.scala
@@ -6,7 +6,6 @@ package akka.actor.typed.internal.receptionist
 
 import akka.actor.typed.internal.ActorRefSerializationSpec
 import akka.actor.typed.receptionist.ServiceKey
-import akka.actor.typed.scaladsl.adapter._
 import akka.serialization.SerializationExtension
 import akka.actor.testkit.typed.scaladsl.ScalaTestWithActorTestKit
 import akka.actor.testkit.typed.scaladsl.LogCapturing
@@ -17,7 +16,7 @@ class ServiceKeySerializationSpec
     with WordSpecLike
     with LogCapturing {
 
-  val serialization = SerializationExtension(system.toClassic)
+  val serialization = SerializationExtension(system)
 
   "ServiceKey[T]" must {
     "be serialized and deserialized by ServiceKeySerializer" in {
diff --git a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/adapter/AdapterSpec.scala b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/adapter/AdapterSpec.scala
index e739a9dc3f..f147b634da 100644
--- a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/adapter/AdapterSpec.scala
+++ b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/adapter/AdapterSpec.scala
@@ -5,7 +5,6 @@
 package akka.actor.typed.scaladsl.adapter
 
 import scala.util.control.NoStackTrace
-
 import akka.actor.InvalidMessageException
 import akka.actor.testkit.typed.TestException
 import akka.actor.typed.scaladsl.Behaviors
@@ -20,6 +19,7 @@ import akka.actor.ActorInitializationException
 import akka.actor.testkit.typed.scaladsl.LogCapturing
 import akka.actor.testkit.typed.scaladsl.LoggingTestKit
 import akka.actor.typed.internal.adapter.SchedulerAdapter
+import akka.serialization.SerializationExtension
 import akka.{ actor => classic }
 import org.scalatest.{ BeforeAndAfterAll, Matchers, WordSpec }
 
@@ -183,6 +183,7 @@ class AdapterSpec extends WordSpec with Matchers with BeforeAndAfterAll with Log
   import AdapterSpec._
 
   implicit val system = akka.actor.ActorSystem("AdapterSpec")
+  def typedSystem: ActorSystem[Nothing] = system.toTyped
 
   "ActorSystem adaption" must {
     "only happen once for a given actor system" in {
@@ -224,6 +225,10 @@ class AdapterSpec extends WordSpec with Matchers with BeforeAndAfterAll with Log
       typedScheduler.getClass should ===(classOf[SchedulerAdapter])
       (typedScheduler.toClassic should be).theSameInstanceAs(system.scheduler)
     }
+
+    "allow seamless access to untyped extensions" in {
+      SerializationExtension(typedSystem) should not be (null)
+    }
   }
 
   "Adapted actors" must {
diff --git a/akka-actor/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-actor/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..9ef2560b7d
--- /dev/null
+++ b/akka-actor/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,12 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.util.ManifestInfo.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.actor.CoordinatedShutdown.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.actor.TypedActor.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.event.AddressTerminatedTopic.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.io.Dns.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.io.Tcp.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.io.Udp.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.io.UdpConnected.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.serialization.SerializationExtension.get")
+
diff --git a/akka-actor/src/main/scala/akka/actor/CoordinatedShutdown.scala b/akka-actor/src/main/scala/akka/actor/CoordinatedShutdown.scala
index ccf97f1229..0aad2ae89a 100644
--- a/akka-actor/src/main/scala/akka/actor/CoordinatedShutdown.scala
+++ b/akka-actor/src/main/scala/akka/actor/CoordinatedShutdown.scala
@@ -181,6 +181,8 @@ object CoordinatedShutdown extends ExtensionId[CoordinatedShutdown] with Extensi
 
   override def get(system: ActorSystem): CoordinatedShutdown = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): CoordinatedShutdown = super.get(system)
+
   override def lookup = CoordinatedShutdown
 
   override def createExtension(system: ExtendedActorSystem): CoordinatedShutdown = {
diff --git a/akka-actor/src/main/scala/akka/actor/Extension.scala b/akka-actor/src/main/scala/akka/actor/Extension.scala
index 97567e04aa..731766d6fe 100644
--- a/akka-actor/src/main/scala/akka/actor/Extension.scala
+++ b/akka-actor/src/main/scala/akka/actor/Extension.scala
@@ -31,6 +31,7 @@ package akka.actor
  *
  *   // Java API: retrieve the extension for the given system.
  *   override def get(system: ActorSystem): UdpExt = super.get(system)
+ *   override def get(system: ClassicActorSystemProvider): UdpExt = super.get(system)
  * }
  *
  * class Ext(system: ExtendedActorSystem) extends Extension {
@@ -77,6 +78,11 @@ trait ExtensionId[T <: Extension] {
     java.util.Objects.requireNonNull(system, "system must not be null!").registerExtension(this)
   }
 
+  /**
+   * Returns an instance of the extension identified by this ExtensionId instance.
+   */
+  def apply(system: ClassicActorSystemProvider): T = apply(system.classicSystem)
+
   /**
    * Returns an instance of the extension identified by this ExtensionId instance.
    * Java API
@@ -89,6 +95,18 @@ trait ExtensionId[T <: Extension] {
    */
   def get(system: ActorSystem): T = apply(system)
 
+  /**
+   * Returns an instance of the extension identified by this ExtensionId instance.
+   * Java API
+   * For extensions written in Scala that are to be used from Java also,
+   * this method should be overridden to get correct return type.
+   * {{{
+   * override def get(system: ClassicActorSystemProvider): TheExtension = super.get(system)
+   * }}}
+   *
+   */
+  def get(system: ClassicActorSystemProvider): T = apply(system)
+
   /**
    * Is used by Akka to instantiate the Extension identified by this ExtensionId,
    * internal use only.
diff --git a/akka-actor/src/main/scala/akka/actor/TypedActor.scala b/akka-actor/src/main/scala/akka/actor/TypedActor.scala
index b0662da676..18ec5bc3a8 100644
--- a/akka-actor/src/main/scala/akka/actor/TypedActor.scala
+++ b/akka-actor/src/main/scala/akka/actor/TypedActor.scala
@@ -106,6 +106,7 @@ trait TypedActorFactory {
 @deprecated("Use 'akka.actor.typed' API.", since = "2.6.0")
 object TypedActor extends ExtensionId[TypedActorExtension] with ExtensionIdProvider {
   override def get(system: ActorSystem): TypedActorExtension = super.get(system)
+  override def get(system: ClassicActorSystemProvider): TypedActorExtension = super.get(system)
 
   def lookup() = this
   def createExtension(system: ExtendedActorSystem): TypedActorExtension = new TypedActorExtension(system)
diff --git a/akka-actor/src/main/scala/akka/event/AddressTerminatedTopic.scala b/akka-actor/src/main/scala/akka/event/AddressTerminatedTopic.scala
index b83f7ad4fb..ea797a0f31 100644
--- a/akka-actor/src/main/scala/akka/event/AddressTerminatedTopic.scala
+++ b/akka-actor/src/main/scala/akka/event/AddressTerminatedTopic.scala
@@ -5,10 +5,12 @@
 package akka.event
 
 import java.util.concurrent.atomic.AtomicReference
+
 import scala.annotation.tailrec
 import akka.actor.ActorRef
 import akka.actor.ActorSystem
 import akka.actor.AddressTerminated
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -24,6 +26,7 @@ import akka.actor.ExtensionIdProvider
  */
 private[akka] object AddressTerminatedTopic extends ExtensionId[AddressTerminatedTopic] with ExtensionIdProvider {
   override def get(system: ActorSystem): AddressTerminatedTopic = super.get(system)
+  override def get(system: ClassicActorSystemProvider): AddressTerminatedTopic = super.get(system)
 
   override def lookup = AddressTerminatedTopic
 
diff --git a/akka-actor/src/main/scala/akka/io/Dns.scala b/akka-actor/src/main/scala/akka/io/Dns.scala
index 935956a680..009b9f5be4 100644
--- a/akka-actor/src/main/scala/akka/io/Dns.scala
+++ b/akka-actor/src/main/scala/akka/io/Dns.scala
@@ -145,6 +145,7 @@ object Dns extends ExtensionId[DnsExt] with ExtensionIdProvider {
    * Java API: retrieve the Udp extension for the given system.
    */
   override def get(system: ActorSystem): DnsExt = super.get(system)
+  override def get(system: ClassicActorSystemProvider): DnsExt = super.get(system)
 }
 
 class DnsExt private[akka] (val system: ExtendedActorSystem, resolverName: String, managerName: String)
diff --git a/akka-actor/src/main/scala/akka/io/Tcp.scala b/akka-actor/src/main/scala/akka/io/Tcp.scala
index d508dd7cb5..7ac471015e 100644
--- a/akka-actor/src/main/scala/akka/io/Tcp.scala
+++ b/akka-actor/src/main/scala/akka/io/Tcp.scala
@@ -48,6 +48,8 @@ object Tcp extends ExtensionId[TcpExt] with ExtensionIdProvider {
    */
   override def get(system: ActorSystem): TcpExt = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): TcpExt = super.get(system)
+
   /**
    * Scala API: this object contains all applicable socket options for TCP.
    *
diff --git a/akka-actor/src/main/scala/akka/io/Udp.scala b/akka-actor/src/main/scala/akka/io/Udp.scala
index 30db041256..d16b294470 100644
--- a/akka-actor/src/main/scala/akka/io/Udp.scala
+++ b/akka-actor/src/main/scala/akka/io/Udp.scala
@@ -40,6 +40,7 @@ object Udp extends ExtensionId[UdpExt] with ExtensionIdProvider {
    * Java API: retrieve the Udp extension for the given system.
    */
   override def get(system: ActorSystem): UdpExt = super.get(system)
+  override def get(system: ClassicActorSystemProvider): UdpExt = super.get(system)
 
   /**
    * The common interface for [[Command]] and [[Event]].
diff --git a/akka-actor/src/main/scala/akka/io/UdpConnected.scala b/akka-actor/src/main/scala/akka/io/UdpConnected.scala
index ac88ec7d4d..c63b303e62 100644
--- a/akka-actor/src/main/scala/akka/io/UdpConnected.scala
+++ b/akka-actor/src/main/scala/akka/io/UdpConnected.scala
@@ -38,6 +38,7 @@ object UdpConnected extends ExtensionId[UdpConnectedExt] with ExtensionIdProvide
    * Java API: retrieve the UdpConnected extension for the given system.
    */
   override def get(system: ActorSystem): UdpConnectedExt = super.get(system)
+  override def get(system: ClassicActorSystemProvider): UdpConnectedExt = super.get(system)
 
   /**
    * The common interface for [[Command]] and [[Event]].
diff --git a/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala b/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala
index 74fc0e8c11..0d22eb5568 100644
--- a/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala
+++ b/akka-actor/src/main/scala/akka/serialization/SerializationExtension.scala
@@ -4,6 +4,7 @@
 
 package akka.serialization
 
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.{ ActorSystem, ExtendedActorSystem, ExtensionId, ExtensionIdProvider }
 
 /**
@@ -12,6 +13,7 @@ import akka.actor.{ ActorSystem, ExtendedActorSystem, ExtensionId, ExtensionIdPr
  */
 object SerializationExtension extends ExtensionId[Serialization] with ExtensionIdProvider {
   override def get(system: ActorSystem): Serialization = super.get(system)
+  override def get(system: ClassicActorSystemProvider): Serialization = super.get(system)
   override def lookup = SerializationExtension
   override def createExtension(system: ExtendedActorSystem): Serialization = new Serialization(system)
 }
diff --git a/akka-actor/src/main/scala/akka/util/ManifestInfo.scala b/akka-actor/src/main/scala/akka/util/ManifestInfo.scala
index 89767a7856..58de6ed7f6 100644
--- a/akka-actor/src/main/scala/akka/util/ManifestInfo.scala
+++ b/akka-actor/src/main/scala/akka/util/ManifestInfo.scala
@@ -11,6 +11,7 @@ import java.util.jar.Attributes
 import java.util.jar.Manifest
 
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -40,6 +41,7 @@ object ManifestInfo extends ExtensionId[ManifestInfo] with ExtensionIdProvider {
     "com.typesafe.play")
 
   override def get(system: ActorSystem): ManifestInfo = super.get(system)
+  override def get(system: ClassicActorSystemProvider): ManifestInfo = super.get(system)
 
   override def lookup(): ManifestInfo.type = ManifestInfo
 
diff --git a/akka-cluster-metrics/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-cluster-metrics/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..1e6c1244bd
--- /dev/null
+++ b/akka-cluster-metrics/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.metrics.ClusterMetricsExtension.get")
+
diff --git a/akka-cluster-metrics/src/main/scala/akka/cluster/metrics/ClusterMetricsExtension.scala b/akka-cluster-metrics/src/main/scala/akka/cluster/metrics/ClusterMetricsExtension.scala
index e0d1bde6da..3f17bd6380 100644
--- a/akka-cluster-metrics/src/main/scala/akka/cluster/metrics/ClusterMetricsExtension.scala
+++ b/akka-cluster-metrics/src/main/scala/akka/cluster/metrics/ClusterMetricsExtension.scala
@@ -10,6 +10,7 @@ import akka.actor.SupervisorStrategy
 import akka.event.LoggingAdapter
 import akka.event.Logging
 import com.typesafe.config.Config
+
 import scala.collection.immutable
 import akka.actor.Props
 import akka.actor.Deploy
@@ -17,6 +18,7 @@ import akka.actor.ExtensionId
 import akka.actor.ExtensionIdProvider
 import akka.actor.ActorSystem
 import akka.actor.ActorRef
+import akka.actor.ClassicActorSystemProvider
 
 /**
  * Cluster metrics extension.
@@ -87,6 +89,7 @@ class ClusterMetricsExtension(system: ExtendedActorSystem) extends Extension {
 object ClusterMetricsExtension extends ExtensionId[ClusterMetricsExtension] with ExtensionIdProvider {
   override def lookup = ClusterMetricsExtension
   override def get(system: ActorSystem): ClusterMetricsExtension = super.get(system)
+  override def get(system: ClassicActorSystemProvider): ClusterMetricsExtension = super.get(system)
   override def createExtension(system: ExtendedActorSystem): ClusterMetricsExtension =
     new ClusterMetricsExtension(system)
 }
diff --git a/akka-cluster-sharding-typed/src/test/scala/akka/cluster/sharding/typed/JoinConfigCompatCheckerClusterShardingSpec.scala b/akka-cluster-sharding-typed/src/test/scala/akka/cluster/sharding/typed/JoinConfigCompatCheckerClusterShardingSpec.scala
index a1b27d16af..fbcfbb4087 100644
--- a/akka-cluster-sharding-typed/src/test/scala/akka/cluster/sharding/typed/JoinConfigCompatCheckerClusterShardingSpec.scala
+++ b/akka-cluster-sharding-typed/src/test/scala/akka/cluster/sharding/typed/JoinConfigCompatCheckerClusterShardingSpec.scala
@@ -8,7 +8,6 @@ import akka.actor.testkit.typed.scaladsl.ActorTestKit
 import akka.actor.testkit.typed.scaladsl.LogCapturing
 import akka.actor.testkit.typed.scaladsl.ScalaTestWithActorTestKit
 import akka.actor.typed.ActorSystem
-import akka.actor.typed.scaladsl.adapter._
 import akka.cluster.{ Cluster => ClassicCluster }
 import akka.testkit.LongRunningTest
 import com.typesafe.config.{ Config, ConfigFactory }
@@ -50,14 +49,14 @@ abstract class JoinConfigCompatCheckerClusterShardingSpec
   protected def join(sys: ActorSystem[_]): ClassicCluster = {
     if (sys eq system) {
       configured(system) should ===(JoinConfig.Shards)
-      val seedNode = ClassicCluster(system.toClassic)
+      val seedNode = ClassicCluster(system)
       seedNode.join(seedNode.selfAddress)
       val probe = createTestProbe()
       probe.awaitAssert(seedNode.readView.isSingletonCluster should ===(true), clusterWaitDuration)
       seedNode
     } else {
-      val joiningNode = ClassicCluster(sys.toClassic)
-      joiningNode.joinSeedNodes(im.Seq(ClassicCluster(system.toClassic).selfAddress))
+      val joiningNode = ClassicCluster(sys)
+      joiningNode.joinSeedNodes(im.Seq(ClassicCluster(system).selfAddress))
       joiningNode
     }
   }
diff --git a/akka-cluster-sharding/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-cluster-sharding/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..c7ba8e0493
--- /dev/null
+++ b/akka-cluster-sharding/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.sharding.ClusterSharding.get")
+
diff --git a/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterSharding.scala b/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterSharding.scala
index 86a9e39868..cd85c6492d 100755
--- a/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterSharding.scala
+++ b/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterSharding.scala
@@ -11,11 +11,11 @@ import java.util.concurrent.ConcurrentHashMap
 import scala.collection.immutable
 import scala.concurrent.Await
 import scala.util.control.NonFatal
-
 import akka.util.ccompat.JavaConverters._
 import akka.actor.Actor
 import akka.actor.ActorRef
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.Deploy
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
@@ -153,6 +153,7 @@ import akka.util.ByteString
 object ClusterSharding extends ExtensionId[ClusterSharding] with ExtensionIdProvider {
 
   override def get(system: ActorSystem): ClusterSharding = super.get(system)
+  override def get(system: ClassicActorSystemProvider): ClusterSharding = super.get(system)
 
   override def lookup = ClusterSharding
 
diff --git a/akka-cluster-tools/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-cluster-tools/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..5e2bf2f62c
--- /dev/null
+++ b/akka-cluster-tools/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,5 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.client.ClusterClientReceptionist.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.pubsub.DistributedPubSub.get")
+
diff --git a/akka-cluster-tools/src/main/scala/akka/cluster/client/ClusterClient.scala b/akka-cluster-tools/src/main/scala/akka/cluster/client/ClusterClient.scala
index 092af156ad..be0406feaf 100644
--- a/akka-cluster-tools/src/main/scala/akka/cluster/client/ClusterClient.scala
+++ b/akka-cluster-tools/src/main/scala/akka/cluster/client/ClusterClient.scala
@@ -8,7 +8,6 @@ import java.net.URLEncoder
 
 import scala.collection.immutable
 import scala.concurrent.duration._
-
 import akka.actor.Actor
 import akka.actor.ActorIdentity
 import akka.actor.ActorLogging
@@ -17,6 +16,7 @@ import akka.actor.ActorRef
 import akka.actor.ActorSystem
 import akka.actor.Address
 import akka.actor.Cancellable
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.DeadLetterSuppression
 import akka.actor.Deploy
 import akka.actor.ExtendedActorSystem
@@ -40,6 +40,7 @@ import com.typesafe.config.Config
 import akka.remote.DeadlineFailureDetector
 import akka.util.MessageBuffer
 import akka.util.ccompat._
+
 import scala.collection.immutable.{ HashMap, HashSet }
 
 @ccompatUsedUntil213
@@ -557,6 +558,7 @@ final class ClusterClient(settings: ClusterClientSettings) extends Actor with Ac
   since = "2.6.0")
 object ClusterClientReceptionist extends ExtensionId[ClusterClientReceptionist] with ExtensionIdProvider {
   override def get(system: ActorSystem): ClusterClientReceptionist = super.get(system)
+  override def get(system: ClassicActorSystemProvider): ClusterClientReceptionist = super.get(system)
 
   override def lookup() = ClusterClientReceptionist
 
diff --git a/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala b/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala
index 5dbe7e57ec..70517710b2 100644
--- a/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala
+++ b/akka-cluster-tools/src/main/scala/akka/cluster/pubsub/DistributedPubSubMediator.scala
@@ -920,6 +920,8 @@ class DistributedPubSubMediator(settings: DistributedPubSubSettings)
 object DistributedPubSub extends ExtensionId[DistributedPubSub] with ExtensionIdProvider {
   override def get(system: ActorSystem): DistributedPubSub = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): DistributedPubSub = super.get(system)
+
   override def lookup = DistributedPubSub
 
   override def createExtension(system: ExtendedActorSystem): DistributedPubSub =
diff --git a/akka-cluster-tools/src/multi-jvm/scala/akka/cluster/TestLeaseActor.scala b/akka-cluster-tools/src/multi-jvm/scala/akka/cluster/TestLeaseActor.scala
index c5e63c49d7..901ea4c4cc 100644
--- a/akka-cluster-tools/src/multi-jvm/scala/akka/cluster/TestLeaseActor.scala
+++ b/akka-cluster-tools/src/multi-jvm/scala/akka/cluster/TestLeaseActor.scala
@@ -8,11 +8,11 @@ import java.util.concurrent.atomic.AtomicReference
 
 import scala.concurrent.Future
 import scala.concurrent.duration._
-
 import akka.actor.Actor
 import akka.actor.ActorLogging
 import akka.actor.ActorRef
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -73,6 +73,7 @@ class TestLeaseActor extends Actor with ActorLogging {
 
 object TestLeaseActorClientExt extends ExtensionId[TestLeaseActorClientExt] with ExtensionIdProvider {
   override def get(system: ActorSystem): TestLeaseActorClientExt = super.get(system)
+  override def get(system: ClassicActorSystemProvider): TestLeaseActorClientExt = super.get(system)
   override def lookup = TestLeaseActorClientExt
   override def createExtension(system: ExtendedActorSystem): TestLeaseActorClientExt =
     new TestLeaseActorClientExt(system)
diff --git a/akka-cluster-tools/src/test/scala/akka/cluster/TestLease.scala b/akka-cluster-tools/src/test/scala/akka/cluster/TestLease.scala
index 92251a929a..89ec6cbe73 100644
--- a/akka-cluster-tools/src/test/scala/akka/cluster/TestLease.scala
+++ b/akka-cluster-tools/src/test/scala/akka/cluster/TestLease.scala
@@ -7,6 +7,7 @@ package akka.cluster
 import java.util.concurrent.ConcurrentHashMap
 import java.util.concurrent.atomic.AtomicReference
 
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.{ ActorSystem, ExtendedActorSystem, Extension, ExtensionId, ExtensionIdProvider }
 import akka.coordination.lease.LeaseSettings
 import akka.coordination.lease.scaladsl.Lease
@@ -19,6 +20,7 @@ import akka.util.ccompat.JavaConverters._
 
 object TestLeaseExt extends ExtensionId[TestLeaseExt] with ExtensionIdProvider {
   override def get(system: ActorSystem): TestLeaseExt = super.get(system)
+  override def get(system: ClassicActorSystemProvider): TestLeaseExt = super.get(system)
   override def lookup = TestLeaseExt
   override def createExtension(system: ExtendedActorSystem): TestLeaseExt = new TestLeaseExt(system)
 }
diff --git a/akka-cluster-typed/src/main/scala/akka/cluster/typed/ClusterSingleton.scala b/akka-cluster-typed/src/main/scala/akka/cluster/typed/ClusterSingleton.scala
index f1971162c3..a6ec99657f 100644
--- a/akka-cluster-typed/src/main/scala/akka/cluster/typed/ClusterSingleton.scala
+++ b/akka-cluster-typed/src/main/scala/akka/cluster/typed/ClusterSingleton.scala
@@ -203,7 +203,6 @@ abstract class ClusterSingleton extends Extension {
 }
 
 object ClusterSingletonManagerSettings {
-  import akka.actor.typed.scaladsl.adapter._
 
   /**
    * Create settings from the default configuration
@@ -211,7 +210,7 @@ object ClusterSingletonManagerSettings {
    */
   def apply(system: ActorSystem[_]): ClusterSingletonManagerSettings =
     apply(system.settings.config.getConfig("akka.cluster.singleton"))
-      .withRemovalMargin(akka.cluster.Cluster(system.toClassic).downingProvider.downRemovalMargin)
+      .withRemovalMargin(akka.cluster.Cluster(system).downingProvider.downRemovalMargin)
 
   /**
    * Create settings from a configuration with the same layout as
diff --git a/akka-cluster-typed/src/main/scala/akka/cluster/typed/internal/AdaptedClusterImpl.scala b/akka-cluster-typed/src/main/scala/akka/cluster/typed/internal/AdaptedClusterImpl.scala
index e4563a514b..17155a3878 100644
--- a/akka-cluster-typed/src/main/scala/akka/cluster/typed/internal/AdaptedClusterImpl.scala
+++ b/akka-cluster-typed/src/main/scala/akka/cluster/typed/internal/AdaptedClusterImpl.scala
@@ -142,7 +142,7 @@ private[akka] final class AdapterClusterImpl(system: ActorSystem[_]) extends Clu
   import AdapterClusterImpl._
 
   require(system.isInstanceOf[ActorSystemAdapter[_]], "only adapted actor systems can be used for cluster features")
-  private val classicCluster = akka.cluster.Cluster(system.toClassic)
+  private val classicCluster = akka.cluster.Cluster(system)
 
   override def selfMember: Member = classicCluster.selfMember
   override def isTerminated: Boolean = classicCluster.isTerminated
diff --git a/akka-cluster-typed/src/test/scala/akka/cluster/typed/ActorSystemSpec.scala b/akka-cluster-typed/src/test/scala/akka/cluster/typed/ActorSystemSpec.scala
index a96498f90f..2352c09db0 100644
--- a/akka-cluster-typed/src/test/scala/akka/cluster/typed/ActorSystemSpec.scala
+++ b/akka-cluster-typed/src/test/scala/akka/cluster/typed/ActorSystemSpec.scala
@@ -72,7 +72,7 @@ class ActorSystemSpec
       akka.remote.classic.netty.tcp.port = 0
       akka.remote.artery.canonical.port = 0
       akka.remote.artery.canonical.hostname = 127.0.0.1
-      
+
       serializers {
           test = "akka.cluster.typed.ActorSystemSpec$$TestSerializer"
         }
@@ -114,8 +114,7 @@ class ActorSystemSpec
         }
         inbox.receiveAll() should ===("hello" :: Nil)
         sys.whenTerminated.futureValue
-        CoordinatedShutdown(sys.toClassic).shutdownReason() should ===(
-          Some(CoordinatedShutdown.ActorSystemTerminateReason))
+        CoordinatedShutdown(sys).shutdownReason() should ===(Some(CoordinatedShutdown.ActorSystemTerminateReason))
       }
     }
 
@@ -150,8 +149,7 @@ class ActorSystemSpec
       // now we know that the guardian has started, and should receive PostStop
       sys.terminate()
       sys.whenTerminated.futureValue
-      CoordinatedShutdown(sys.toClassic).shutdownReason() should ===(
-        Some(CoordinatedShutdown.ActorSystemTerminateReason))
+      CoordinatedShutdown(sys).shutdownReason() should ===(Some(CoordinatedShutdown.ActorSystemTerminateReason))
       inbox.receiveAll() should ===("done" :: Nil)
     }
 
diff --git a/akka-cluster-typed/src/test/scala/akka/cluster/typed/internal/receptionist/ClusterReceptionistSpec.scala b/akka-cluster-typed/src/test/scala/akka/cluster/typed/internal/receptionist/ClusterReceptionistSpec.scala
index 417a77c72a..dbd6fe4905 100644
--- a/akka-cluster-typed/src/test/scala/akka/cluster/typed/internal/receptionist/ClusterReceptionistSpec.scala
+++ b/akka-cluster-typed/src/test/scala/akka/cluster/typed/internal/receptionist/ClusterReceptionistSpec.scala
@@ -17,7 +17,6 @@ import akka.actor.typed.ActorRef
 import akka.actor.typed.receptionist.Receptionist
 import akka.actor.typed.receptionist.ServiceKey
 import akka.actor.typed.scaladsl.Behaviors
-import akka.actor.typed.scaladsl.adapter._
 import akka.cluster.MemberStatus
 import akka.cluster.typed.Cluster
 import akka.cluster.typed.Down
@@ -210,7 +209,7 @@ class ClusterReceptionistSpec extends WordSpec with Matchers with LogCapturing {
 
         regProbe2.expectMessageType[Listing].serviceInstances(PingKey).size should ===(2)
 
-        akka.cluster.Cluster(system1.toClassic).shutdown()
+        akka.cluster.Cluster(system1).shutdown()
 
         regProbe2.expectNoMessage(3.seconds)
 
diff --git a/akka-cluster-typed/src/test/scala/docs/akka/cluster/typed/DistributedPubSubExample.scala b/akka-cluster-typed/src/test/scala/docs/akka/cluster/typed/DistributedPubSubExample.scala
index 3e47cd356d..01b6960906 100644
--- a/akka-cluster-typed/src/test/scala/docs/akka/cluster/typed/DistributedPubSubExample.scala
+++ b/akka-cluster-typed/src/test/scala/docs/akka/cluster/typed/DistributedPubSubExample.scala
@@ -87,8 +87,7 @@ object Publisher {
       Behaviors.setup[AnyRef] { context =>
         import akka.cluster.pubsub.DistributedPubSub
         import akka.cluster.pubsub.DistributedPubSubMediator
-        import akka.actor.typed.scaladsl.adapter._
-        val mediator = DistributedPubSub(context.system.toClassic).mediator
+        val mediator = DistributedPubSub(context.system).mediator
 
         var registry: Map[DataKey, DataType] = Map.empty
 
@@ -263,8 +262,7 @@ object DataPlatform {
   def apply(): Behavior[ProvisionCommand] = {
     Behaviors.setup { context =>
       //#mediator
-      import akka.actor.typed.scaladsl.adapter._
-      val mediator = DistributedPubSub(context.system.toClassic).mediator
+      val mediator = DistributedPubSub(context.system).mediator
       //#mediator
       val service = context.spawn(DataService(mediator), "data")
 
@@ -337,7 +335,7 @@ object DistributedPubSubExample {
 
     // provision new data type
     val platformProbe = TestProbe[DataApi]()(system)
-    val mediator = DistributedPubSub(system.toClassic).mediator
+    val mediator = DistributedPubSub(system).mediator
     mediator ! DistributedPubSubMediator.Subscribe(IngestionTopic, platformProbe.ref.toClassic)
 
     system ! ProvisionDataType(key, "dummy-schema", platformProbe.ref)
diff --git a/akka-cluster/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-cluster/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..81ca3b809a
--- /dev/null
+++ b/akka-cluster/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.Cluster.get")
+
diff --git a/akka-cluster/src/main/scala/akka/cluster/Cluster.scala b/akka-cluster/src/main/scala/akka/cluster/Cluster.scala
index 91bf56b206..3ed3a97a3f 100644
--- a/akka-cluster/src/main/scala/akka/cluster/Cluster.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/Cluster.scala
@@ -35,6 +35,8 @@ import com.github.ghik.silencer.silent
 object Cluster extends ExtensionId[Cluster] with ExtensionIdProvider {
   override def get(system: ActorSystem): Cluster = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): Cluster = super.get(system)
+
   override def lookup = Cluster
 
   override def createExtension(system: ExtendedActorSystem): Cluster = new Cluster(system)
diff --git a/akka-coordination/src/main/scala/akka/coordination/lease/javadsl/LeaseProvider.scala b/akka-coordination/src/main/scala/akka/coordination/lease/javadsl/LeaseProvider.scala
index 8bc439dd5b..8c9af5312d 100644
--- a/akka-coordination/src/main/scala/akka/coordination/lease/javadsl/LeaseProvider.scala
+++ b/akka-coordination/src/main/scala/akka/coordination/lease/javadsl/LeaseProvider.scala
@@ -4,12 +4,14 @@
 
 package akka.coordination.lease.javadsl
 
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.{ ActorSystem, ExtendedActorSystem, Extension, ExtensionId, ExtensionIdProvider }
 import akka.coordination.lease.internal.LeaseAdapter
 import akka.coordination.lease.scaladsl.{ LeaseProvider => ScalaLeaseProvider }
 
 object LeaseProvider extends ExtensionId[LeaseProvider] with ExtensionIdProvider {
   override def get(system: ActorSystem): LeaseProvider = super.get(system)
+  override def get(system: ClassicActorSystemProvider): LeaseProvider = super.get(system)
 
   override def lookup = LeaseProvider
 
diff --git a/akka-coordination/src/main/scala/akka/coordination/lease/scaladsl/LeaseProvider.scala b/akka-coordination/src/main/scala/akka/coordination/lease/scaladsl/LeaseProvider.scala
index f5c6413d91..c8e81e32a4 100644
--- a/akka-coordination/src/main/scala/akka/coordination/lease/scaladsl/LeaseProvider.scala
+++ b/akka-coordination/src/main/scala/akka/coordination/lease/scaladsl/LeaseProvider.scala
@@ -10,6 +10,7 @@ import java.util.function.{ Function => JFunction }
 import scala.collection.immutable
 import scala.util.{ Failure, Success, Try }
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -19,6 +20,7 @@ import akka.coordination.lease.LeaseSettings
 
 object LeaseProvider extends ExtensionId[LeaseProvider] with ExtensionIdProvider {
   override def get(system: ActorSystem): LeaseProvider = super.get(system)
+  override def get(system: ClassicActorSystemProvider): LeaseProvider = super.get(system)
 
   override def lookup = LeaseProvider
 
diff --git a/akka-discovery/src/main/scala/akka/discovery/Discovery.scala b/akka-discovery/src/main/scala/akka/discovery/Discovery.scala
index 2b2b0a7ebf..762fe268ce 100644
--- a/akka-discovery/src/main/scala/akka/discovery/Discovery.scala
+++ b/akka-discovery/src/main/scala/akka/discovery/Discovery.scala
@@ -103,6 +103,8 @@ object Discovery extends ExtensionId[Discovery] with ExtensionIdProvider {
 
   override def get(system: ActorSystem): Discovery = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): Discovery = super.get(system)
+
   override def createExtension(system: ExtendedActorSystem): Discovery = new Discovery()(system)
 
   /**
diff --git a/akka-distributed-data/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-distributed-data/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..3cd3a28174
--- /dev/null
+++ b/akka-distributed-data/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.ddata.DistributedData.get")
+
diff --git a/akka-distributed-data/src/main/scala/akka/cluster/ddata/DistributedData.scala b/akka-distributed-data/src/main/scala/akka/cluster/ddata/DistributedData.scala
index d69d79d727..f28ca8e081 100644
--- a/akka-distributed-data/src/main/scala/akka/cluster/ddata/DistributedData.scala
+++ b/akka-distributed-data/src/main/scala/akka/cluster/ddata/DistributedData.scala
@@ -6,6 +6,7 @@ package akka.cluster.ddata
 
 import akka.actor.ActorRef
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -15,6 +16,7 @@ import akka.event.Logging
 
 object DistributedData extends ExtensionId[DistributedData] with ExtensionIdProvider {
   override def get(system: ActorSystem): DistributedData = super.get(system)
+  override def get(system: ClassicActorSystemProvider): DistributedData = super.get(system)
 
   override def lookup = DistributedData
 
diff --git a/akka-docs/src/test/java/jdocs/persistence/ResumableProjectionExample.java b/akka-docs/src/test/java/jdocs/persistence/ResumableProjectionExample.java
index 7c40f9a160..ffc20ab965 100644
--- a/akka-docs/src/test/java/jdocs/persistence/ResumableProjectionExample.java
+++ b/akka-docs/src/test/java/jdocs/persistence/ResumableProjectionExample.java
@@ -10,7 +10,6 @@ import akka.actor.typed.ActorSystem;
 import akka.actor.typed.Behavior;
 import akka.actor.typed.javadsl.AbstractBehavior;
 import akka.actor.typed.javadsl.ActorContext;
-import akka.actor.typed.javadsl.Adapter;
 import akka.actor.typed.javadsl.Behaviors;
 import akka.actor.typed.javadsl.Receive;
 import akka.actor.typed.javadsl.AskPattern;
@@ -31,7 +30,7 @@ public interface ResumableProjectionExample {
       throws Exception {
 
     final MyJavadslReadJournal readJournal =
-        PersistenceQuery.get(Adapter.toClassic(system))
+        PersistenceQuery.get(system)
             .getReadJournalFor(
                 MyJavadslReadJournal.class, "akka.persistence.query.my-read-journal");
 
diff --git a/akka-docs/src/test/scala/docs/extension/ExtensionDocSpec.scala b/akka-docs/src/test/scala/docs/extension/ExtensionDocSpec.scala
index 85750d66c1..f3e6086370 100644
--- a/akka-docs/src/test/scala/docs/extension/ExtensionDocSpec.scala
+++ b/akka-docs/src/test/scala/docs/extension/ExtensionDocSpec.scala
@@ -5,7 +5,9 @@
 package docs.extension
 
 import java.util.concurrent.atomic.AtomicLong
+
 import akka.actor.Actor
+import akka.actor.ClassicActorSystemProvider
 import akka.testkit.AkkaSpec
 
 //#extension
@@ -42,6 +44,7 @@ object CountExtension extends ExtensionId[CountExtensionImpl] with ExtensionIdPr
    * Java API: retrieve the Count extension for the given system.
    */
   override def get(system: ActorSystem): CountExtensionImpl = super.get(system)
+  override def get(system: ClassicActorSystemProvider): CountExtensionImpl = super.get(system)
 }
 //#extensionid
 
diff --git a/akka-docs/src/test/scala/docs/extension/SettingsExtensionDocSpec.scala b/akka-docs/src/test/scala/docs/extension/SettingsExtensionDocSpec.scala
index cf10e53b32..bff5d57556 100644
--- a/akka-docs/src/test/scala/docs/extension/SettingsExtensionDocSpec.scala
+++ b/akka-docs/src/test/scala/docs/extension/SettingsExtensionDocSpec.scala
@@ -10,10 +10,13 @@ import akka.actor.Extension
 import akka.actor.ExtensionId
 import akka.actor.ExtensionIdProvider
 import akka.actor.ExtendedActorSystem
+
 import scala.concurrent.duration.Duration
 import com.typesafe.config.Config
 import java.util.concurrent.TimeUnit
 
+import akka.actor.ClassicActorSystemProvider
+
 //#imports
 
 import akka.actor.Actor
@@ -39,6 +42,7 @@ object Settings extends ExtensionId[SettingsImpl] with ExtensionIdProvider {
    * Java API: retrieve the Settings extension for the given system.
    */
   override def get(system: ActorSystem): SettingsImpl = super.get(system)
+  override def get(system: ClassicActorSystemProvider): SettingsImpl = super.get(system)
 }
 //#extensionid
 
diff --git a/akka-multi-node-testkit/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-multi-node-testkit/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..d59d7d1f4e
--- /dev/null
+++ b/akka-multi-node-testkit/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.remote.testconductor.TestConductor.get")
+
diff --git a/akka-multi-node-testkit/src/main/scala/akka/remote/testconductor/Extension.scala b/akka-multi-node-testkit/src/main/scala/akka/remote/testconductor/Extension.scala
index e2919d971f..e7d2354507 100644
--- a/akka-multi-node-testkit/src/main/scala/akka/remote/testconductor/Extension.scala
+++ b/akka-multi-node-testkit/src/main/scala/akka/remote/testconductor/Extension.scala
@@ -4,6 +4,7 @@
 
 package akka.remote.testconductor
 
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.{ ActorContext, ActorSystem, ExtendedActorSystem, Extension, ExtensionId, ExtensionIdProvider }
 import akka.remote.RemoteActorRefProvider
 import akka.util.Timeout
@@ -30,6 +31,7 @@ object TestConductor extends ExtensionId[TestConductorExt] with ExtensionIdProvi
    * Java API: retrieve the TestConductor extension for the given system.
    */
   override def get(system: ActorSystem): TestConductorExt = super.get(system)
+  override def get(system: ClassicActorSystemProvider): TestConductorExt = super.get(system)
 
   def apply()(implicit ctx: ActorContext): TestConductorExt = apply(ctx.system)
 
diff --git a/akka-persistence-query/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-persistence-query/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..d3a9331d47
--- /dev/null
+++ b/akka-persistence-query/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.persistence.query.PersistenceQuery.get")
+
diff --git a/akka-persistence-query/src/main/scala/akka/persistence/query/PersistenceQuery.scala b/akka-persistence-query/src/main/scala/akka/persistence/query/PersistenceQuery.scala
index 1808ce89cf..5d7ee48d17 100644
--- a/akka-persistence-query/src/main/scala/akka/persistence/query/PersistenceQuery.scala
+++ b/akka-persistence-query/src/main/scala/akka/persistence/query/PersistenceQuery.scala
@@ -18,10 +18,8 @@ import scala.reflect.ClassTag
  */
 object PersistenceQuery extends ExtensionId[PersistenceQuery] with ExtensionIdProvider {
 
-  /**
-   * Java API.
-   */
   override def get(system: ActorSystem): PersistenceQuery = super.get(system)
+  override def get(system: ClassicActorSystemProvider): PersistenceQuery = super.get(system)
 
   def createExtension(system: ExtendedActorSystem): PersistenceQuery = new PersistenceQuery(system)
 
diff --git a/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedBehaviorSpec.scala b/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedBehaviorSpec.scala
index 2ade41b6aa..de757ce07c 100644
--- a/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedBehaviorSpec.scala
+++ b/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedBehaviorSpec.scala
@@ -283,10 +283,9 @@ class EventSourcedBehaviorSpec
     with LogCapturing {
 
   import EventSourcedBehaviorSpec._
-  import akka.actor.typed.scaladsl.adapter._
 
   val queries: LeveldbReadJournal =
-    PersistenceQuery(system.toClassic).readJournalFor[LeveldbReadJournal](LeveldbReadJournal.Identifier)
+    PersistenceQuery(system).readJournalFor[LeveldbReadJournal](LeveldbReadJournal.Identifier)
 
   val pidCounter = new AtomicInteger(0)
   private def nextPid(): PersistenceId = PersistenceId.ofUniqueId(s"c${pidCounter.incrementAndGet()})")
diff --git a/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedEventAdapterSpec.scala b/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedEventAdapterSpec.scala
index 268377c635..b90ba5c5b6 100644
--- a/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedEventAdapterSpec.scala
+++ b/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/EventSourcedEventAdapterSpec.scala
@@ -96,13 +96,11 @@ class EventSourcedEventAdapterSpec
     State
   }
 
-  import akka.actor.typed.scaladsl.adapter._
-
   val pidCounter = new AtomicInteger(0)
   private def nextPid(): PersistenceId = PersistenceId.ofUniqueId(s"c${pidCounter.incrementAndGet()})")
 
   val queries: LeveldbReadJournal =
-    PersistenceQuery(system.toClassic).readJournalFor[LeveldbReadJournal](LeveldbReadJournal.Identifier)
+    PersistenceQuery(system).readJournalFor[LeveldbReadJournal](LeveldbReadJournal.Identifier)
 
   private def behavior(pid: PersistenceId, probe: ActorRef[String]): EventSourcedBehavior[String, String, String] =
     EventSourcedBehavior(pid, "", commandHandler = { (_, command) =>
diff --git a/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/SnapshotRecoveryWithEmptyJournalSpec.scala b/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/SnapshotRecoveryWithEmptyJournalSpec.scala
index fdcc8cec0d..8d3e38219a 100644
--- a/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/SnapshotRecoveryWithEmptyJournalSpec.scala
+++ b/akka-persistence-typed/src/test/scala/akka/persistence/typed/scaladsl/SnapshotRecoveryWithEmptyJournalSpec.scala
@@ -12,7 +12,6 @@ import akka.actor.testkit.typed.scaladsl.ScalaTestWithActorTestKit
 import akka.actor.typed.ActorRef
 import akka.actor.typed.Behavior
 import akka.actor.typed.scaladsl.Behaviors
-import akka.actor.typed.scaladsl.adapter._
 import akka.persistence.serialization.Snapshot
 import akka.persistence.typed.PersistenceId
 import akka.serialization.Serialization
@@ -64,7 +63,7 @@ class SnapshotRecoveryWithEmptyJournalSpec
 
   val snapshotsDir: File = new File(survivingSnapshotPath)
 
-  val serializationExtension: Serialization = SerializationExtension(system.toClassic)
+  val serializationExtension: Serialization = SerializationExtension(system)
 
   val persistenceId: String = system.name
 
diff --git a/akka-persistence/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-persistence/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..0dc201b334
--- /dev/null
+++ b/akka-persistence/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,6 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.persistence.fsm.SnapshotAfter.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.persistence.Persistence.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.persistence.journal.PersistencePluginProxyExtension.get")
+
diff --git a/akka-persistence/src/main/scala/akka/persistence/Persistence.scala b/akka-persistence/src/main/scala/akka/persistence/Persistence.scala
index 59b70f19a4..082a1c69ec 100644
--- a/akka-persistence/src/main/scala/akka/persistence/Persistence.scala
+++ b/akka-persistence/src/main/scala/akka/persistence/Persistence.scala
@@ -158,6 +158,8 @@ object Persistence extends ExtensionId[Persistence] with ExtensionIdProvider {
   /** Java API. */
   override def get(system: ActorSystem): Persistence = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): Persistence = super.get(system)
+
   def createExtension(system: ExtendedActorSystem): Persistence = new Persistence(system)
 
   def lookup() = Persistence
diff --git a/akka-persistence/src/main/scala/akka/persistence/fsm/PersistentFSM.scala b/akka-persistence/src/main/scala/akka/persistence/fsm/PersistentFSM.scala
index a41e72b12a..3c699cc4fa 100644
--- a/akka-persistence/src/main/scala/akka/persistence/fsm/PersistentFSM.scala
+++ b/akka-persistence/src/main/scala/akka/persistence/fsm/PersistentFSM.scala
@@ -24,6 +24,8 @@ import scala.reflect.ClassTag
 private[akka] object SnapshotAfter extends ExtensionId[SnapshotAfter] with ExtensionIdProvider {
   override def get(system: ActorSystem): SnapshotAfter = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): SnapshotAfter = super.get(system)
+
   override def lookup = SnapshotAfter
 
   override def createExtension(system: ExtendedActorSystem): SnapshotAfter = new SnapshotAfter(system.settings.config)
diff --git a/akka-persistence/src/main/scala/akka/persistence/journal/PersistencePluginProxy.scala b/akka-persistence/src/main/scala/akka/persistence/journal/PersistencePluginProxy.scala
index 38319682ac..4d1fe13490 100644
--- a/akka-persistence/src/main/scala/akka/persistence/journal/PersistencePluginProxy.scala
+++ b/akka-persistence/src/main/scala/akka/persistence/journal/PersistencePluginProxy.scala
@@ -68,6 +68,7 @@ object PersistencePluginProxyExtension
     new PersistencePluginProxyExtensionImpl(system)
   override def lookup(): ExtensionId[_ <: Extension] = PersistencePluginProxyExtension
   override def get(system: ActorSystem): PersistencePluginProxyExtensionImpl = super.get(system)
+  override def get(system: ClassicActorSystemProvider): PersistencePluginProxyExtensionImpl = super.get(system)
 }
 
 final class PersistencePluginProxy(config: Config) extends Actor with Stash with ActorLogging {
diff --git a/akka-persistence/src/test/scala/akka/persistence/PersistentActorJournalProtocolSpec.scala b/akka-persistence/src/test/scala/akka/persistence/PersistentActorJournalProtocolSpec.scala
index 4e48b6bafb..206008055a 100644
--- a/akka-persistence/src/test/scala/akka/persistence/PersistentActorJournalProtocolSpec.scala
+++ b/akka-persistence/src/test/scala/akka/persistence/PersistentActorJournalProtocolSpec.scala
@@ -82,6 +82,7 @@ object JournalPuppet extends ExtensionId[JournalProbe] with ExtensionIdProvider
     new JournalProbe()(system)
 
   override def get(system: ActorSystem): JournalProbe = super.get(system)
+  override def get(system: ClassicActorSystemProvider): JournalProbe = super.get(system)
 }
 class JournalProbe(implicit private val system: ExtendedActorSystem) extends Extension {
   val probe = TestProbe()
diff --git a/akka-remote/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-remote/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..48213461d5
--- /dev/null
+++ b/akka-remote/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,7 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.remote.AddressUidExtension.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.remote.BoundAddressesExtension.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.remote.RemoteMetricsExtension.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.remote.serialization.ActorRefResolveThreadLocalCache.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.remote.transport.TransportAdaptersExtension.get")
diff --git a/akka-remote/src/main/scala/akka/remote/AddressUidExtension.scala b/akka-remote/src/main/scala/akka/remote/AddressUidExtension.scala
index 5756b842b1..4d2b8c5683 100644
--- a/akka-remote/src/main/scala/akka/remote/AddressUidExtension.scala
+++ b/akka-remote/src/main/scala/akka/remote/AddressUidExtension.scala
@@ -5,7 +5,9 @@
 package akka.remote
 
 import java.util.concurrent.ThreadLocalRandom
+
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -21,6 +23,7 @@ import akka.actor.ExtensionIdProvider
  */
 object AddressUidExtension extends ExtensionId[AddressUidExtension] with ExtensionIdProvider {
   override def get(system: ActorSystem): AddressUidExtension = super.get(system)
+  override def get(system: ClassicActorSystemProvider): AddressUidExtension = super.get(system)
 
   override def lookup = AddressUidExtension
 
diff --git a/akka-remote/src/main/scala/akka/remote/BoundAddressesExtension.scala b/akka-remote/src/main/scala/akka/remote/BoundAddressesExtension.scala
index 772b8dc377..ae6357f08e 100644
--- a/akka-remote/src/main/scala/akka/remote/BoundAddressesExtension.scala
+++ b/akka-remote/src/main/scala/akka/remote/BoundAddressesExtension.scala
@@ -6,6 +6,7 @@ package akka.remote
 
 import akka.actor.ActorSystem
 import akka.actor.Address
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -17,6 +18,7 @@ import akka.remote.artery.ArteryTransport
  */
 object BoundAddressesExtension extends ExtensionId[BoundAddressesExtension] with ExtensionIdProvider {
   override def get(system: ActorSystem): BoundAddressesExtension = super.get(system)
+  override def get(system: ClassicActorSystemProvider): BoundAddressesExtension = super.get(system)
 
   override def lookup = BoundAddressesExtension
 
diff --git a/akka-remote/src/main/scala/akka/remote/RemoteMetricsExtension.scala b/akka-remote/src/main/scala/akka/remote/RemoteMetricsExtension.scala
index aace1fe9b2..e562fd5c30 100644
--- a/akka-remote/src/main/scala/akka/remote/RemoteMetricsExtension.scala
+++ b/akka-remote/src/main/scala/akka/remote/RemoteMetricsExtension.scala
@@ -7,9 +7,9 @@ package akka.remote
 import java.util.concurrent.ConcurrentHashMap
 
 import scala.annotation.tailrec
-
 import akka.actor.ActorSelectionMessage
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -26,6 +26,7 @@ import com.github.ghik.silencer.silent
 @silent("deprecated")
 private[akka] object RemoteMetricsExtension extends ExtensionId[RemoteMetrics] with ExtensionIdProvider {
   override def get(system: ActorSystem): RemoteMetrics = super.get(system)
+  override def get(system: ClassicActorSystemProvider): RemoteMetrics = super.get(system)
 
   override def lookup = RemoteMetricsExtension
 
diff --git a/akka-remote/src/main/scala/akka/remote/serialization/ActorRefResolveCache.scala b/akka-remote/src/main/scala/akka/remote/serialization/ActorRefResolveCache.scala
index 732bc80422..a2b2f8da40 100644
--- a/akka-remote/src/main/scala/akka/remote/serialization/ActorRefResolveCache.scala
+++ b/akka-remote/src/main/scala/akka/remote/serialization/ActorRefResolveCache.scala
@@ -6,6 +6,7 @@ package akka.remote.serialization
 
 import akka.actor.ActorRef
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.EmptyLocalActorRef
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
@@ -23,6 +24,7 @@ private[akka] object ActorRefResolveThreadLocalCache
     with ExtensionIdProvider {
 
   override def get(system: ActorSystem): ActorRefResolveThreadLocalCache = super.get(system)
+  override def get(system: ClassicActorSystemProvider): ActorRefResolveThreadLocalCache = super.get(system)
 
   override def lookup = ActorRefResolveThreadLocalCache
 
diff --git a/akka-remote/src/main/scala/akka/remote/transport/AbstractTransportAdapter.scala b/akka-remote/src/main/scala/akka/remote/transport/AbstractTransportAdapter.scala
index 3e42c3fe20..14757c6583 100644
--- a/akka-remote/src/main/scala/akka/remote/transport/AbstractTransportAdapter.scala
+++ b/akka-remote/src/main/scala/akka/remote/transport/AbstractTransportAdapter.scala
@@ -49,6 +49,7 @@ class TransportAdapters(system: ExtendedActorSystem) extends Extension {
 @deprecated("Classic remoting is deprecated, use Artery", "2.6.0")
 object TransportAdaptersExtension extends ExtensionId[TransportAdapters] with ExtensionIdProvider {
   override def get(system: ActorSystem): TransportAdapters = super.get(system)
+  override def get(system: ClassicActorSystemProvider): TransportAdapters = super.get(system)
   override def lookup = TransportAdaptersExtension
   override def createExtension(system: ExtendedActorSystem): TransportAdapters =
     new TransportAdapters(system)
diff --git a/akka-remote/src/test/scala/akka/remote/artery/MetadataCarryingSpec.scala b/akka-remote/src/test/scala/akka/remote/artery/MetadataCarryingSpec.scala
index dbf936dbb0..24f17689c1 100644
--- a/akka-remote/src/test/scala/akka/remote/artery/MetadataCarryingSpec.scala
+++ b/akka-remote/src/test/scala/akka/remote/artery/MetadataCarryingSpec.scala
@@ -18,6 +18,7 @@ import akka.testkit.JavaSerializable
 
 object MetadataCarryingSpy extends ExtensionId[MetadataCarryingSpy] with ExtensionIdProvider {
   override def get(system: ActorSystem): MetadataCarryingSpy = super.get(system)
+  override def get(system: ClassicActorSystemProvider): MetadataCarryingSpy = super.get(system)
   override def lookup = MetadataCarryingSpy
   override def createExtension(system: ExtendedActorSystem): MetadataCarryingSpy = new MetadataCarryingSpy
 
diff --git a/akka-serialization-jackson/src/main/scala/akka/serialization/jackson/JacksonObjectMapperProvider.scala b/akka-serialization-jackson/src/main/scala/akka/serialization/jackson/JacksonObjectMapperProvider.scala
index 51761c0d4a..f1e23b818d 100644
--- a/akka-serialization-jackson/src/main/scala/akka/serialization/jackson/JacksonObjectMapperProvider.scala
+++ b/akka-serialization-jackson/src/main/scala/akka/serialization/jackson/JacksonObjectMapperProvider.scala
@@ -12,6 +12,7 @@ import scala.compat.java8.OptionConverters._
 import scala.util.Failure
 import scala.util.Success
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.DynamicAccess
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
@@ -44,6 +45,7 @@ import com.fasterxml.jackson.databind.json.JsonMapper
 
 object JacksonObjectMapperProvider extends ExtensionId[JacksonObjectMapperProvider] with ExtensionIdProvider {
   override def get(system: ActorSystem): JacksonObjectMapperProvider = super.get(system)
+  override def get(system: ClassicActorSystemProvider): JacksonObjectMapperProvider = super.get(system)
 
   override def lookup = JacksonObjectMapperProvider
 
diff --git a/akka-stream/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-stream/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..6cd9e49627
--- /dev/null
+++ b/akka-stream/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,8 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.stream.javadsl.Tcp.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.stream.scaladsl.Tcp.apply")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.stream.scaladsl.Tcp.get")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("com.typesafe.sslconfig.akka.AkkaSSLConfig.apply")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("com.typesafe.sslconfig.akka.AkkaSSLConfig.get")
+
diff --git a/akka-stream/src/main/scala/akka/stream/StreamRefs.scala b/akka-stream/src/main/scala/akka/stream/StreamRefs.scala
index 2a59aefc76..1180cd0871 100644
--- a/akka-stream/src/main/scala/akka/stream/StreamRefs.scala
+++ b/akka-stream/src/main/scala/akka/stream/StreamRefs.scala
@@ -7,6 +7,7 @@ package akka.stream
 import akka.NotUsed
 import akka.actor.ActorRef
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
 import akka.actor.ExtensionId
@@ -120,11 +121,8 @@ final case class InvalidPartnerActorException(expectedRef: ActorRef, gotRef: Act
  * The stream ref resolver extension provides a way to serialize and deserialize streamrefs in user serializers.
  */
 object StreamRefResolver extends ExtensionId[StreamRefResolver] {
-
-  /**
-   * Java API
-   */
   override def get(system: ActorSystem): StreamRefResolver = super.get(system)
+  override def get(system: ClassicActorSystemProvider): StreamRefResolver = super.get(system)
 
   override def createExtension(system: ExtendedActorSystem): StreamRefResolver =
     new StreamRefResolverImpl(system)
diff --git a/akka-stream/src/main/scala/akka/stream/SystemMaterializer.scala b/akka-stream/src/main/scala/akka/stream/SystemMaterializer.scala
index 1916c7d5b7..ee634de66b 100644
--- a/akka-stream/src/main/scala/akka/stream/SystemMaterializer.scala
+++ b/akka-stream/src/main/scala/akka/stream/SystemMaterializer.scala
@@ -5,6 +5,7 @@
 package akka.stream
 
 import akka.actor.ActorSystem
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.Deploy
 import akka.actor.ExtendedActorSystem
 import akka.actor.Extension
@@ -29,6 +30,7 @@ import com.github.ghik.silencer.silent
  */
 object SystemMaterializer extends ExtensionId[SystemMaterializer] with ExtensionIdProvider {
   override def get(system: ActorSystem): SystemMaterializer = super.get(system)
+  override def get(system: ClassicActorSystemProvider): SystemMaterializer = super.get(system)
 
   override def lookup = SystemMaterializer
 
diff --git a/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala b/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala
index 96fb8e9907..fb309497a6 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala
@@ -174,6 +174,7 @@ private[akka] class SubFusingActorMaterializerImpl(
  */
 @InternalApi private[akka] object FlowNames extends ExtensionId[FlowNames] with ExtensionIdProvider {
   override def get(system: ActorSystem): FlowNames = super.get(system)
+  override def get(system: ClassicActorSystemProvider): FlowNames = super.get(system)
   override def lookup() = FlowNames
   override def createExtension(system: ExtendedActorSystem): FlowNames = new FlowNames
 }
diff --git a/akka-stream/src/main/scala/akka/stream/impl/streamref/StreamRefsMaster.scala b/akka-stream/src/main/scala/akka/stream/impl/streamref/StreamRefsMaster.scala
index dd3f295f1e..d9e8be1f65 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/streamref/StreamRefsMaster.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/streamref/StreamRefsMaster.scala
@@ -4,6 +4,7 @@
 
 package akka.stream.impl.streamref
 
+import akka.actor.ClassicActorSystemProvider
 import akka.actor.{ ActorSystem, ExtendedActorSystem, Extension, ExtensionId, ExtensionIdProvider }
 import akka.annotation.InternalApi
 import akka.stream.impl.SeqActorName
@@ -18,6 +19,7 @@ private[stream] object StreamRefsMaster extends ExtensionId[StreamRefsMaster] wi
   override def lookup(): StreamRefsMaster.type = this
 
   override def get(system: ActorSystem): StreamRefsMaster = super.get(system)
+  override def get(system: ClassicActorSystemProvider): StreamRefsMaster = super.get(system)
 }
 
 /** INTERNAL API */
diff --git a/akka-stream/src/main/scala/akka/stream/javadsl/Tcp.scala b/akka-stream/src/main/scala/akka/stream/javadsl/Tcp.scala
index fc8932eda6..c570052035 100644
--- a/akka-stream/src/main/scala/akka/stream/javadsl/Tcp.scala
+++ b/akka-stream/src/main/scala/akka/stream/javadsl/Tcp.scala
@@ -130,6 +130,8 @@ object Tcp extends ExtensionId[Tcp] with ExtensionIdProvider {
 
   override def get(system: ActorSystem): Tcp = super.get(system)
 
+  override def get(system: ClassicActorSystemProvider): Tcp = super.get(system)
+
   def lookup() = Tcp
 
   def createExtension(system: ExtendedActorSystem): Tcp = new Tcp(system)
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/Tcp.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/Tcp.scala
index ca38d3861c..d65f0ea485 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/Tcp.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/Tcp.scala
@@ -81,6 +81,7 @@ object Tcp extends ExtensionId[Tcp] with ExtensionIdProvider {
   def apply()(implicit system: ActorSystem): Tcp = super.apply(system)
 
   override def get(system: ActorSystem): Tcp = super.get(system)
+  override def get(system: ClassicActorSystemProvider): Tcp = super.get(system)
 
   def lookup() = Tcp
 
diff --git a/akka-stream/src/main/scala/com/typesafe/sslconfig/akka/AkkaSSLConfig.scala b/akka-stream/src/main/scala/com/typesafe/sslconfig/akka/AkkaSSLConfig.scala
index a332a8757d..6f98467417 100644
--- a/akka-stream/src/main/scala/com/typesafe/sslconfig/akka/AkkaSSLConfig.scala
+++ b/akka-stream/src/main/scala/com/typesafe/sslconfig/akka/AkkaSSLConfig.scala
@@ -22,6 +22,7 @@ object AkkaSSLConfig extends ExtensionId[AkkaSSLConfig] with ExtensionIdProvider
   //////////////////// EXTENSION SETUP ///////////////////
 
   override def get(system: ActorSystem): AkkaSSLConfig = super.get(system)
+  override def get(system: ClassicActorSystemProvider): AkkaSSLConfig = super.get(system)
   def apply()(implicit system: ActorSystem): AkkaSSLConfig = super.apply(system)
 
   override def lookup() = AkkaSSLConfig
diff --git a/akka-testkit/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes b/akka-testkit/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
new file mode 100644
index 0000000000..1b84c101aa
--- /dev/null
+++ b/akka-testkit/src/main/mima-filters/2.6.0.backwards.excludes/28294-add-ExtensionId-apply-get-overloads.excludes
@@ -0,0 +1,4 @@
+# Incompatibilities against Akka < 2.5.17 where extra static bridge methods were generated that
+# Mima now wrongly correlates with the new ones added in the PR
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.testkit.TestKitExtension.get")
+
diff --git a/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala b/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala
index 20952826df..0d59812a13 100644
--- a/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/TestKitExtension.scala
@@ -4,13 +4,16 @@
 
 package akka.testkit
 
+import akka.actor.ClassicActorSystemProvider
 import com.typesafe.config.Config
 import akka.util.Timeout
 import akka.actor.{ ActorSystem, ExtendedActorSystem, Extension, ExtensionId }
+
 import scala.concurrent.duration.FiniteDuration
 
 object TestKitExtension extends ExtensionId[TestKitSettings] {
   override def get(system: ActorSystem): TestKitSettings = super.get(system)
+  override def get(system: ClassicActorSystemProvider): TestKitSettings = super.get(system)
   def createExtension(system: ExtendedActorSystem): TestKitSettings = new TestKitSettings(system.settings.config)
 }