pjfanning · Sep 13, 2026 · Sep 12, 2026
diff --git a/...a-test/src/test/scala/org/apache/pekko/projection/cassandra/CassandraProjectionSpec.scala b/...a-test/src/test/scala/org/apache/pekko/projection/cassandra/CassandraProjectionSpec.scala
@@ -18,7 +18,6 @@ import java.util.concurrent.atomic.AtomicInteger
 import java.util.concurrent.atomic.AtomicReference
 
 import scala.annotation.tailrec
-import scala.collection.immutable
 import scala.concurrent.Await
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
@@ -584,10 +583,10 @@ class CassandraProjectionSpec
       val entityId = UUID.randomUUID().toString
       val projectionId = genRandomProjectionId()
 
-      def groupedHandler(): Handler[immutable.Seq[Envelope]] = new Handler[immutable.Seq[Envelope]] {
+      def groupedHandler(): Handler[Seq[Envelope]] = new Handler[Seq[Envelope]] {
         private var state: Future[Option[ConcatStr]] = repository.findById(entityId)
 
-        override def process(group: immutable.Seq[Envelope]): Future[Done] = {
+        override def process(group: Seq[Envelope]): Future[Done] = {
           val newState = state.flatMap { s =>
             val concatStr = group.foldLeft(s) {
               case (None, env)      => Some(ConcatStr(env.id, env.message))

diff --git a/...a/src/main/scala/org/apache/pekko/projection/cassandra/scaladsl/CassandraProjection.scala b/...a/src/main/scala/org/apache/pekko/projection/cassandra/scaladsl/CassandraProjection.scala
@@ -13,7 +13,6 @@
 
 package org.apache.pekko.projection.cassandra.scaladsl
 
-import scala.collection.immutable
 import scala.concurrent.Future
 import scala.concurrent.duration.Duration
 
@@ -88,7 +87,7 @@ object CassandraProjection {
   def groupedWithin[Offset, Envelope](
       projectionId: ProjectionId,
       sourceProvider: SourceProvider[Offset, Envelope],
-      handler: () => Handler[immutable.Seq[Envelope]]): GroupedProjection[Offset, Envelope] =
+      handler: () => Handler[Seq[Envelope]]): GroupedProjection[Offset, Envelope] =
     new CassandraProjectionImpl(
       projectionId,
       sourceProvider,

diff --git a/core-test/src/test/scala/org/apache/pekko/projection/internal/OffsetSerializationSpec.scala b/core-test/src/test/scala/org/apache/pekko/projection/internal/OffsetSerializationSpec.scala
@@ -17,8 +17,6 @@ import java.nio.charset.StandardCharsets
 import java.util.Base64
 import java.util.UUID
 
-import scala.collection.immutable
-
 import org.apache.pekko
 import pekko.actor.ExtendedActorSystem
 import pekko.actor.testkit.typed.scaladsl.LogCapturing
@@ -140,7 +138,7 @@ class OffsetSerializationSpec
       }
 
       val storageRepresentation = MultipleOffsets(
-        immutable.Seq(SingleOffset(ProjectionId(id.name, surrogateProjectionKey), LongManifest, "1", mergeable = true)))
+        Seq(SingleOffset(ProjectionId(id.name, surrogateProjectionKey), LongManifest, "1", mergeable = true)))
 
       actualRep shouldBe storageRepresentation
 
@@ -155,7 +153,7 @@ class OffsetSerializationSpec
       val mergeableOffset =
         MergeableOffset(Map(surrogateProjectionKey1 -> 1L, surrogateProjectionKey2 -> 2L))
       val storageRepresentation = MultipleOffsets(
-        immutable.Seq(
+        Seq(
           SingleOffset(ProjectionId(projectionName, surrogateProjectionKey1), LongManifest, "1", mergeable = true),
           SingleOffset(ProjectionId(projectionName, surrogateProjectionKey2), LongManifest, "2", mergeable = true)))
 

diff --git a/...g/apache/pekko/projection/internal/metrics/tools/InternalProjectionStateMetricsSpec.scala b/...g/apache/pekko/projection/internal/metrics/tools/InternalProjectionStateMetricsSpec.scala
@@ -15,7 +15,6 @@ package org.apache.pekko.projection.internal.metrics.tools
 
 import java.util.UUID
 
-import scala.collection.immutable
 import scala.concurrent.Await
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
@@ -161,8 +160,8 @@ object InternalProjectionStateMetricsSpec {
           }
           case groupedHandlerStrategy: GroupedHandlerStrategy[Envelope] @unchecked => {
             val adaptedHandler = () =>
-              new Handler[immutable.Seq[Envelope]] {
-                override def process(envelopes: immutable.Seq[Envelope]): Future[Done] =
+              new Handler[Seq[Envelope]] {
+                override def process(envelopes: Seq[Envelope]): Future[Done] =
                   groupedHandlerStrategy.handlerFactory().process(envelopes).flatMap { _ =>
                     offsetStore.saveOffset(projectionId, envelopes.last.offset)
                   }

diff --git a/...test/src/test/scala/org/apache/pekko/projection/internal/metrics/tools/TestHandlers.scala b/...test/src/test/scala/org/apache/pekko/projection/internal/metrics/tools/TestHandlers.scala
@@ -13,7 +13,6 @@
 
 package org.apache.pekko.projection.internal.metrics.tools
 
-import scala.collection.immutable
 import scala.concurrent.Future
 
 import org.apache.pekko
@@ -71,13 +70,13 @@ object TestHandlers {
    *                       trigger an error and then be removed from the stack. To fail an item multiple times
    *                       add its offset repeatedly. Uses `Int` instead of `Long` for convenience.
    */
-  def groupedWithErrors(erroredOffsets: Int*): () => Handler[immutable.Seq[Envelope]] = {
+  def groupedWithErrors(erroredOffsets: Int*): () => Handler[Seq[Envelope]] = {
     var nextProcessStrategy = ProcessStrategy(erroredOffsets.map {
       _.toLong
     }.toList)
     () =>
-      new Handler[immutable.Seq[Envelope]] {
-        override def process(envelopes: immutable.Seq[Envelope]): Future[Done] = {
+      new Handler[Seq[Envelope]] {
+        override def process(envelopes: Seq[Envelope]): Future[Done] = {
           nextProcessStrategy match {
             case SomeFailures(nextFail :: tail)
                 if envelopes

diff --git a/core/src/main/scala/org/apache/pekko/projection/internal/HandlerAdapter.scala b/core/src/main/scala/org/apache/pekko/projection/internal/HandlerAdapter.scala
@@ -13,7 +13,6 @@
 
 package org.apache.pekko.projection.internal
 
-import scala.collection.immutable
 import scala.concurrent.Future
 import scala.jdk.CollectionConverters._
 import scala.jdk.FutureConverters._
@@ -55,13 +54,13 @@ import pekko.projection.scaladsl
 }
 
 /**
- * INTERNAL API: Adapter from `javadsl.Handler[java.util.List[Envelope]]` to `scaladsl.Handler[immutable.Seq[Envelope]]`
+ * INTERNAL API: Adapter from `javadsl.Handler[java.util.List[Envelope]]` to `scaladsl.Handler[Seq[Envelope]]`
  */
 @InternalApi private[projection] class GroupedHandlerAdapter[Envelope](
     delegate: javadsl.Handler[java.util.List[Envelope]])
-    extends scaladsl.Handler[immutable.Seq[Envelope]] {
+    extends scaladsl.Handler[Seq[Envelope]] {
 
-  override def process(envelopes: immutable.Seq[Envelope]): Future[Done] = {
+  override def process(envelopes: Seq[Envelope]): Future[Done] = {
     delegate.process(envelopes.asJava).asScala
   }
 

diff --git a/core/src/main/scala/org/apache/pekko/projection/internal/InternalProjectionState.scala b/core/src/main/scala/org/apache/pekko/projection/internal/InternalProjectionState.scala
@@ -13,7 +13,6 @@
 
 package org.apache.pekko.projection.internal
 
-import scala.collection.immutable
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
 import scala.concurrent.Promise
@@ -89,7 +88,7 @@ private[projection] abstract class InternalProjectionState[Offset, Envelope](
 
   protected def saveOffsetsAndReport(
       projectionId: ProjectionId,
-      batch: immutable.Seq[ProjectionContextImpl[Offset, Envelope]]): Future[Done] = {
+      batch: Seq[ProjectionContextImpl[Offset, Envelope]]): Future[Done] = {
 
     // The batch contains multiple projections contexts. Each of these contexts may represent
     // a single envelope or a group of envelopes. The size of the batch and the size of the
@@ -103,15 +102,15 @@ private[projection] abstract class InternalProjectionState[Offset, Envelope](
   /**
    * A convenience method to serialize asynchronous operations to occur one after another is complete
    */
-  private def serialize(batches: Map[String, immutable.Seq[ProjectionContextImpl[Offset, Envelope]]])(
-      op: (String, immutable.Seq[ProjectionContextImpl[Offset, Envelope]]) => Future[Done]): Future[Done] = {
+  private def serialize(batches: Map[String, Seq[ProjectionContextImpl[Offset, Envelope]]])(
+      op: (String, Seq[ProjectionContextImpl[Offset, Envelope]]) => Future[Done]): Future[Done] = {
 
     val logProgressEvery: Int = 5
     val size = batches.size
     logger.debug("Processing [{}] partitioned batches serially", size)
 
     def loop(
-        remaining: List[(String, immutable.Seq[ProjectionContextImpl[Offset, Envelope]])],
+        remaining: List[(String, Seq[ProjectionContextImpl[Offset, Envelope]])],
         n: Int): Future[Done] = {
       remaining match {
         case Nil                  => Future.successful(Done)
@@ -247,11 +246,11 @@ private[projection] abstract class InternalProjectionState[Offset, Envelope](
       HandlerRecoveryImpl[Offset, Envelope](projectionId, recoveryStrategy, logger, statusObserver, telemetry)
 
     def processGrouped(
-        handler: Handler[immutable.Seq[Envelope]],
+        handler: Handler[Seq[Envelope]],
         handlerRecovery: HandlerRecoveryImpl[Offset, Envelope],
-        envelopesAndOffsets: immutable.Seq[ProjectionContextImpl[Offset, Envelope]]): Future[Done] = {
+        envelopesAndOffsets: Seq[ProjectionContextImpl[Offset, Envelope]]): Future[Done] = {
 
-      def processEnvelopes(partitioned: immutable.Seq[ProjectionContextImpl[Offset, Envelope]]): Future[Done] = {
+      def processEnvelopes(partitioned: Seq[ProjectionContextImpl[Offset, Envelope]]): Future[Done] = {
         val first = partitioned.head
         val firstOffset = first.offset
         val lastOffset = partitioned.last.offset

diff --git a/core/src/main/scala/org/apache/pekko/projection/internal/OffsetSerialization.scala b/core/src/main/scala/org/apache/pekko/projection/internal/OffsetSerialization.scala
@@ -16,8 +16,6 @@ package org.apache.pekko.projection.internal
 import java.util.Base64
 import java.util.UUID
 
-import scala.collection.immutable
-
 import org.apache.pekko
 import pekko.actor.typed.ActorSystem
 import pekko.annotation.InternalApi
@@ -34,7 +32,7 @@ import pekko.serialization.Serializers
   sealed trait StorageRepresentation
   final case class SingleOffset(id: ProjectionId, manifest: String, offsetStr: String, mergeable: Boolean = false)
       extends StorageRepresentation
-  final case class MultipleOffsets(reps: immutable.Seq[SingleOffset]) extends StorageRepresentation
+  final case class MultipleOffsets(reps: Seq[SingleOffset]) extends StorageRepresentation
 
   final val StringManifest = "STR"
   final val LongManifest = "LNG"

diff --git a/core/src/main/scala/org/apache/pekko/projection/internal/OffsetStrategy.scala b/core/src/main/scala/org/apache/pekko/projection/internal/OffsetStrategy.scala
@@ -13,7 +13,6 @@
 
 package org.apache.pekko.projection.internal
 
-import scala.collection.immutable
 import scala.concurrent.duration.FiniteDuration
 
 import org.apache.pekko
@@ -128,10 +127,10 @@ private[projection] final case class SingleHandlerStrategy[Envelope](handlerFact
  */
 @InternalApi
 private[projection] final case class GroupedHandlerStrategy[Envelope](
-    handlerFactory: () => Handler[immutable.Seq[Envelope]],
+    handlerFactory: () => Handler[Seq[Envelope]],
     afterEnvelopes: Option[Int] = None,
     orAfterDuration: Option[FiniteDuration] = None)
-    extends FunctionHandlerStrategy[immutable.Seq[Envelope]](handlerFactory)
+    extends FunctionHandlerStrategy[Seq[Envelope]](handlerFactory)
 
 /**
  * INTERNAL API

diff --git a/core/src/main/scala/org/apache/pekko/projection/internal/Telemetry.scala b/core/src/main/scala/org/apache/pekko/projection/internal/Telemetry.scala
@@ -15,7 +15,6 @@ package org.apache.pekko.projection.internal
 
 import java.util
 
-import scala.collection.immutable
 import scala.jdk.CollectionConverters._
 
 import org.apache.pekko
@@ -122,7 +121,7 @@ trait Telemetry {
     dynamicAccess
       .createInstanceFor[Telemetry](
         fqcn,
-        immutable.Seq((classOf[ProjectionId], projectionId), (classOf[ActorSystem[?]], system)))
+        Seq((classOf[ProjectionId], projectionId), (classOf[ActorSystem[?]], system)))
       .get
   }
 }

diff --git a/docs/src/main/paradox/cassandra.md b/docs/src/main/paradox/cassandra.md
@@ -82,7 +82,7 @@ The envelopes are grouped within a time window, or limited by a number of envelo
 This window can be defined with `withGroup` of the returned `GroupedProjection`. The default settings for
 the window is defined in configuration section `pekko.projection.grouped`.
 
-When using `groupedWithin` the handler is a @scala[`Handler[immutable.Seq[EventEnvelope[ShoppingCart.Event]]]`]@java[`Handler<List<EventEnvelope<ShoppingCart.Event>>>`].
+When using `groupedWithin` the handler is a @scala[`Handler[Seq[EventEnvelope[ShoppingCart.Event]]]`]@java[`Handler<List<EventEnvelope<ShoppingCart.Event>>>`].
 The @ref:[`GroupedShoppingCartHandler` is shown below](#grouped-handler).
 
 It stores the offset in Cassandra immediately after the `handler` has processed the envelopes, but that

diff --git a/docs/src/main/paradox/jdbc.md b/docs/src/main/paradox/jdbc.md
@@ -125,7 +125,7 @@ The envelopes are grouped within a time window, or limited by a number of envelo
 This window can be defined with `withGroup` of the returned `GroupedProjection`. The default settings for
 the window is defined in configuration section `pekko.projection.grouped`.
 
-When using `groupedWithin` the handler is a @scala[`JdbcHandler[immutable.Seq[EventEnvelope[ShoppingCart.Event]]]`]@java[`JdbcHandler<List<EventEnvelope<ShoppingCart.Event>>>`].
+When using `groupedWithin` the handler is a @scala[`JdbcHandler[Seq[EventEnvelope[ShoppingCart.Event]]]`]@java[`JdbcHandler<List<EventEnvelope<ShoppingCart.Event>>>`].
 The @ref:[`GroupedShoppingCartHandler` is shown below](#grouped-handler).
 
 The offset is stored in the same transaction used for the user defined `handler`, which means exactly-once

diff --git a/docs/src/main/paradox/r2dbc.md b/docs/src/main/paradox/r2dbc.md
@@ -160,7 +160,7 @@ The envelopes are grouped within a time window, or limited by a number of envelo
 This window can be defined with `withGroup` of the returned `GroupedProjection`. The default settings for
 the window is defined in configuration section `pekko.projection.grouped`.
 
-When using `groupedWithin` the handler is a @scala[`R2dbcHandler[immutable.Seq[EventEnvelope[ShoppingCart.Event]]]`]@java[`R2dbcHandler<List<EventEnvelope<ShoppingCart.Event>>>`].
+When using `groupedWithin` the handler is a @scala[`R2dbcHandler[Seq[EventEnvelope[ShoppingCart.Event]]]`]@java[`R2dbcHandler<List<EventEnvelope<ShoppingCart.Event>>>`].
 The @ref:[`GroupedShoppingCartHandler` is shown below](#grouped-handler).
 
 The offset is stored in the same transaction used for the user defined `handler`, which means exactly-once

diff --git a/docs/src/main/paradox/slick.md b/docs/src/main/paradox/slick.md
@@ -74,7 +74,7 @@ The envelopes are grouped within a time window, or limited by a number of envelo
 This window can be defined with `withGroup` of the returned `GroupedProjection`. The default settings for
 the window is defined in configuration section `pekko.projection.grouped`.
 
-When using `groupedWithin` the handler is a `SlickHandler[immutable.Seq[EventEnvelope[ShoppingCart.Event]]]`.
+When using `groupedWithin` the handler is a `SlickHandler[Seq[EventEnvelope[ShoppingCart.Event]]]`.
 The @ref:[`GroupedShoppingCartHandler` is shown below](#grouped-handler).
 
 The offset is stored in the same transaction as the `DBIO` returned from the `handler`, which means exactly-once

diff --git a/...rc/main/scala/org/apache/pekko/projection/state/scaladsl/DurableStateSourceProvider.scala b/...rc/main/scala/org/apache/pekko/projection/state/scaladsl/DurableStateSourceProvider.scala
@@ -13,7 +13,6 @@
 
 package org.apache.pekko.projection.state.scaladsl
 
-import scala.collection.immutable
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
 
@@ -112,7 +111,7 @@ object DurableStateSourceProvider {
   def sliceRanges(
       system: ActorSystem[?],
       durableStateStoreQueryPluginId: String,
-      numberOfRanges: Int): immutable.Seq[Range] =
+      numberOfRanges: Int): Seq[Range] =
     DurableStateStoreRegistry(system)
       .durableStateStoreFor[DurableStateStoreBySliceQuery[Any]](durableStateStoreQueryPluginId)
       .sliceRanges(numberOfRanges)

diff --git a/...c/main/scala/org/apache/pekko/projection/eventsourced/scaladsl/EventSourcedProvider.scala b/...c/main/scala/org/apache/pekko/projection/eventsourced/scaladsl/EventSourcedProvider.scala
@@ -15,7 +15,6 @@ package org.apache.pekko.projection.eventsourced.scaladsl
 
 import java.time.Instant
 
-import scala.collection.immutable
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
 import com.typesafe.config.Config
@@ -141,15 +140,15 @@ object EventSourcedProvider {
       .readJournalFor[EventsBySliceQuery](readJournalPluginId, readJournalConfig)
       .sliceForPersistenceId(persistenceId)
 
-  def sliceRanges(system: ActorSystem[?], readJournalPluginId: String, numberOfRanges: Int): immutable.Seq[Range] =
+  def sliceRanges(system: ActorSystem[?], readJournalPluginId: String, numberOfRanges: Int): Seq[Range] =
     PersistenceQuery(system).readJournalFor[EventsBySliceQuery](readJournalPluginId).sliceRanges(numberOfRanges)
 
   /** @since 2.0.0 */
   def sliceRanges(
       system: ActorSystem[?],
       readJournalPluginId: String,
       readJournalConfig: Config,
-      numberOfRanges: Int): immutable.Seq[Range] =
+      numberOfRanges: Int): Seq[Range] =
     PersistenceQuery(system)
       .readJournalFor[EventsBySliceQuery](readJournalPluginId, readJournalConfig)
       .sliceRanges(numberOfRanges)

diff --git a/...est/scala/org/apache/pekko/projection/eventsourced/scaldsl/EventSourcedProviderSpec.scala b/...est/scala/org/apache/pekko/projection/eventsourced/scaldsl/EventSourcedProviderSpec.scala
@@ -17,7 +17,6 @@
 
 package org.apache.pekko.projection.eventsourced.scaldsl
 
-import scala.collection.immutable.Seq
 import scala.concurrent.Future
 import com.typesafe.config.ConfigFactory
 import org.apache.pekko

diff --git a/examples/src/test/scala/docs/jdbc/JdbcProjectionDocExample.scala b/examples/src/test/scala/docs/jdbc/JdbcProjectionDocExample.scala
@@ -99,15 +99,13 @@ object JdbcProjectionDocExample {
   // #handler
 
   // #grouped-handler
-  import scala.collection.immutable
-
   class GroupedShoppingCartHandler(repository: OrderRepository)
-      extends JdbcHandler[immutable.Seq[EventEnvelope[ShoppingCart.Event]], PlainJdbcSession] {
+      extends JdbcHandler[Seq[EventEnvelope[ShoppingCart.Event]], PlainJdbcSession] {
     private val logger = LoggerFactory.getLogger(getClass)
 
     override def process(
         session: PlainJdbcSession,
-        envelopes: immutable.Seq[EventEnvelope[ShoppingCart.Event]]): Unit = {
+        envelopes: Seq[EventEnvelope[ShoppingCart.Event]]): Unit = {
 
       // save all events in DB
       envelopes.map(_.event).foreach {

diff --git a/examples/src/test/scala/docs/slick/SlickProjectionDocExample.scala b/examples/src/test/scala/docs/slick/SlickProjectionDocExample.scala
@@ -94,13 +94,11 @@ class SlickProjectionDocExample {
   // #handler
 
   // #grouped-handler
-  import scala.collection.immutable
-
   class GroupedShoppingCartHandler(repository: OrderRepository)(implicit ec: ExecutionContext)
-      extends SlickHandler[immutable.Seq[EventEnvelope[ShoppingCart.Event]]] {
+      extends SlickHandler[Seq[EventEnvelope[ShoppingCart.Event]]] {
     private val logger = LoggerFactory.getLogger(getClass)
 
-    override def process(envelopes: immutable.Seq[EventEnvelope[ShoppingCart.Event]]): DBIO[Done] = {
+    override def process(envelopes: Seq[EventEnvelope[ShoppingCart.Event]]): DBIO[Done] = {
       val dbios = envelopes.map(_.event).map {
         case ShoppingCart.CheckedOut(cartId, time) =>
           logger.info(s"Shopping cart $cartId was checked out at $time")

diff --git a/...t/src/test/scala/org/apache/pekko/projection/grpc/internal/EventProducerServiceSpec.scala b/...t/src/test/scala/org/apache/pekko/projection/grpc/internal/EventProducerServiceSpec.scala
@@ -54,7 +54,6 @@ import org.scalatest.wordspec.AnyWordSpecLike
 
 import java.time.Instant
 import java.util.concurrent.ConcurrentHashMap
-import scala.collection.immutable
 import scala.concurrent.Future
 import scala.concurrent.Promise
 
@@ -92,7 +91,7 @@ object EventProducerServiceSpec {
     override def sliceForPersistenceId(persistenceId: String): Int =
       persistenceExt.sliceForPersistenceId(persistenceId)
 
-    override def sliceRanges(numberOfRanges: Int): immutable.Seq[Range] =
+    override def sliceRanges(numberOfRanges: Int): Seq[Range] =
       persistenceExt.sliceRanges(numberOfRanges)
   }
 }