diff --git a/build.sbt b/build.sbt
index 80c4f7d74e..210ed0eeb7 100644
--- a/build.sbt
+++ b/build.sbt
@@ -115,7 +115,7 @@ val scalaCollectionCompatVersion = "2.14.0"
 val scalaMacrosVersion = "2.1.1"
 val scalatestVersion = "3.2.19"
 val shapelessVersion = "2.3.13"
-val sparkeyVersion = "3.5.1"
+val sparkeyVersion = "3.7.0"
 val tensorFlowVersion = "1.1.0"
 val tensorFlowMetadataVersion = "1.16.1"
 val testContainersVersion = "0.44.1"
@@ -330,6 +330,17 @@ ThisBuild / mimaBinaryIssueFilters ++= Seq(
   ),
   ProblemFilters.exclude[MissingClassProblem](
     "org.apache.beam.sdk.extensions.sorter.BufferedExternalSorter$Options"
+  ),
+  // Private method sparkeySideInput(String, Function1) replaced by sparkeySideInputWithConfig
+  ProblemFilters.exclude[IncompatibleMethTypeProblem](
+    "com.spotify.scio.extra.sparkey.package#SparkeyScioContext.sparkeySideInput$extension"
+  ),
+  // Scala 2.12 generates different extension method names
+  ProblemFilters.exclude[DirectMissingMethodProblem](
+    "com.spotify.scio.extra.sparkey.package#SparkeyScioContext.sparkeySideInput$extension0"
+  ),
+  ProblemFilters.exclude[DirectMissingMethodProblem](
+    "com.spotify.scio.extra.sparkey.package#SparkeyScioContext.sparkeySideInput$extension1"
   )
 )
 
diff --git a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyReadConfig.scala b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyReadConfig.scala
new file mode 100644
index 0000000000..9809cec10d
--- /dev/null
+++ b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyReadConfig.scala
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2026 Spotify AB.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package com.spotify.scio.extra.sparkey
+
+import com.spotify.sparkey.LoadMode
+
+/**
+ * Configuration for reading Sparkey side inputs.
+ *
+ * @param loadMode
+ *   page cache prefetch mode for mmap-backed shards. Ignored for heap-backed shards.
+ * @param heapBudgetBytes
+ *   maximum bytes to read into JVM heap across all shards in this side input. Shards are loaded
+ *   largest-first to maximize heap utilization. Shards that don't fit within the remaining budget
+ *   fall back to memory-mapped files. Default is 0 (all mmap, matching current behavior).
+ */
+case class SparkeyReadConfig(
+  loadMode: LoadMode = LoadMode.NONE,
+  heapBudgetBytes: Long = 0
+)
+
+object SparkeyReadConfig {
+  val Default: SparkeyReadConfig = SparkeyReadConfig()
+}
diff --git a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyUri.scala b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyUri.scala
index f0d4ed4e0d..697c2b735f 100644
--- a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyUri.scala
+++ b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/SparkeyUri.scala
@@ -29,6 +29,8 @@ import org.apache.beam.sdk.options.PipelineOptions
 
 import java.nio.file.Path
 import java.util.UUID
+import org.slf4j.LoggerFactory
+
 import scala.collection.mutable
 import scala.jdk.CollectionConverters._
 
@@ -76,11 +78,16 @@ case class SparkeyUri(path: String) {
     rfu.download(downloadPaths.asJava).asScala
   }
 
-  def getReader(rfu: RemoteFileUtil): SparkeyReader = {
+  def getReader(rfu: RemoteFileUtil): SparkeyReader =
+    getReader(rfu, SparkeyReadConfig.Default)
+
+  def getReader(rfu: RemoteFileUtil, config: SparkeyReadConfig): SparkeyReader = {
     if (!isSharded) {
-      val path =
+      val file =
         if (isLocal) new File(basePath) else downloadRemoteUris(Seq(basePath), rfu).head.toFile
-      Sparkey.open(path)
+      val totalSize = Sparkey.getIndexFile(file).length() + Sparkey.getLogFile(file).length()
+      val useHeap = config.heapBudgetBytes > 0 && totalSize <= config.heapBudgetBytes
+      Sparkey.reader().file(file).useHeap(useHeap).open()
     } else {
       val (basePaths, numShards) =
         ShardedSparkeyUri.basePathsAndCount(EmptyMatchTreatment.DISALLOW, globExpression)
@@ -91,7 +98,10 @@ case class SparkeyUri(path: String) {
             .map(_.toAbsolutePath.toString.replaceAll("\\.sp[il]$", ""))
             .toSet
         }
-      new ShardedSparkeyReader(ShardedSparkeyUri.localReadersByShard(paths), numShards)
+      new ShardedSparkeyReader(
+        ShardedSparkeyUri.localReadersByShard(paths, config.heapBudgetBytes),
+        numShards
+      )
     }
   }
 
@@ -129,11 +139,75 @@ private[sparkey] object ShardedSparkeyUri {
   private[sparkey] def localReadersByShard(
     localBasePaths: Iterable[String]
   ): Map[Short, SparkeyReader] =
-    localBasePaths.iterator.map { path =>
-      val (shardIndex, _) = shardsFromPath(path)
-      val reader = Sparkey.open(new File(path + ".spi"))
-      (shardIndex, reader)
-    }.toMap
+    localReadersByShard(localBasePaths, 0)
+
+  private[sparkey] def localReadersByShard(
+    localBasePaths: Iterable[String],
+    heapBudgetBytes: Long
+  ): Map[Short, SparkeyReader] = {
+    if (heapBudgetBytes <= 0) {
+      // No heap budget — all mmap (current behavior)
+      localBasePaths.iterator.map { path =>
+        val (shardIndex, _) = shardsFromPath(path)
+        val reader = Sparkey.open(new File(path + ".spi"))
+        (shardIndex, reader)
+      }.toMap
+    } else {
+      // Sort shards largest-first for greedy budget allocation
+      val shardsWithSize = localBasePaths
+        .map { path =>
+          val (shardIndex, _) = shardsFromPath(path)
+          val file = new File(path + ".spi")
+          val size = Sparkey.getIndexFile(file).length() + Sparkey.getLogFile(file).length()
+          (shardIndex, path, size)
+        }
+        .toSeq
+        .sortBy(-_._3)
+
+      case class Acc(
+        readers: List[(Short, SparkeyReader)] = Nil,
+        remainingBudget: Long = heapBudgetBytes,
+        heapShards: Int = 0,
+        mmapShards: Int = 0
+      )
+
+      val result = shardsWithSize.foldLeft(Acc()) { case (acc, (shardIndex, path, size)) =>
+        val file = new File(path + ".spi")
+        val useHeap = size <= acc.remainingBudget
+        val reader = Sparkey.reader().file(file).useHeap(useHeap).open()
+        if (useHeap) {
+          acc.copy(
+            readers = (shardIndex, reader) :: acc.readers,
+            remainingBudget = acc.remainingBudget - size,
+            heapShards = acc.heapShards + 1
+          )
+        } else {
+          acc.copy(
+            readers = (shardIndex, reader) :: acc.readers,
+            mmapShards = acc.mmapShards + 1
+          )
+        }
+      }
+
+      val logger = LoggerFactory.getLogger(classOf[ShardedSparkeyReader])
+      val totalSize = shardsWithSize.map(_._3).sum
+      val heapBytes = heapBudgetBytes - result.remainingBudget
+      logger.info(
+        "Opened {} shards: {} on heap ({} bytes), {} mmap. " +
+          "Total data: {} bytes, heap budget: {} bytes",
+        Array[AnyRef](
+          Integer.valueOf(result.heapShards + result.mmapShards),
+          Integer.valueOf(result.heapShards),
+          java.lang.Long.valueOf(heapBytes),
+          Integer.valueOf(result.mmapShards),
+          java.lang.Long.valueOf(totalSize),
+          java.lang.Long.valueOf(heapBudgetBytes)
+        ): _*
+      )
+
+      result.readers.toMap
+    }
+  }
 
   def basePathsAndCount(
     emptyMatchTreatment: EmptyMatchTreatment,
diff --git a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/instances/ShardedSparkeyReader.scala b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/instances/ShardedSparkeyReader.scala
index af372b2c2d..30b3cf5565 100644
--- a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/instances/ShardedSparkeyReader.scala
+++ b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/instances/ShardedSparkeyReader.scala
@@ -18,7 +18,7 @@ package com.spotify.scio.extra.sparkey.instances
 
 import java.util
 
-import com.spotify.sparkey.{IndexHeader, LogHeader, SparkeyReader}
+import com.spotify.sparkey.{IndexHeader, LoadMode, LoadResult, LogHeader, SparkeyReader}
 
 import scala.util.hashing.MurmurHash3
 import scala.jdk.CollectionConverters._
@@ -81,6 +81,9 @@ class ShardedSparkeyReader(val sparkeys: Map[Short, SparkeyReader], val numShard
   override def iterator(): util.Iterator[SparkeyReader.Entry] =
     sparkeys.values.map(_.iterator.asScala).reduce(_ ++ _).asJava
 
+  override def load(mode: LoadMode, executor: java.util.concurrent.Executor): LoadResult =
+    LoadResult.combine(sparkeys.values.map(_.load(mode, executor)).toArray: _*)
+
   override def getLoadedBytes: Long = sparkeys.valuesIterator.map(_.getLoadedBytes).sum
 
   override def getTotalBytes: Long = sparkeys.valuesIterator.map(_.getTotalBytes).sum
diff --git a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/package.scala b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/package.scala
index f14b27dcd5..c2d54f7406 100644
--- a/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/package.scala
+++ b/scio-extra/src/main/scala/com/spotify/scio/extra/sparkey/package.scala
@@ -113,7 +113,11 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
   /** Enhanced version of [[ScioContext]] with Sparkey methods. */
   implicit class SparkeyScioContext(private val self: ScioContext) extends AnyVal {
 
-    private def sparkeySideInput[T](basePath: String, mapFn: SparkeyReader => T): SideInput[T] = {
+    private def sparkeySideInputWithConfig[T](
+      basePath: String,
+      mapFn: SparkeyReader => T,
+      config: SparkeyReadConfig
+    ): SideInput[T] = {
       if (self.isTest) {
         val id = self.testId.get
         val view = TestDataManager
@@ -126,7 +130,7 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
         val view: PCollectionView[SparkeyUri] = self
           .parallelize(paths)
           .applyInternal(View.asSingleton())
-        new SparkeySideInput(view, mapFn)
+        new SparkeySideInput(view, mapFn, config)
       }
     }
 
@@ -138,7 +142,21 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
      */
     @experimental
     def sparkeySideInput(basePath: String): SideInput[SparkeyReader] =
-      sparkeySideInput(basePath, identity)
+      sparkeySideInputWithConfig(basePath, identity, SparkeyReadConfig.Default)
+
+    /**
+     * Create a SideInput of `SparkeyReader` from a [[SparkeyUri]] base path, to be used with
+     * [[com.spotify.scio.values.SCollection.withSideInputs SCollection.withSideInputs]]. If the
+     * provided base path ends with "*", it will be treated as a sharded collection of Sparkey
+     * files.
+     *
+     * @param config
+     *   read configuration including page cache prefetch mode and heap budget for loading shards
+     *   into JVM heap memory instead of memory-mapped files.
+     */
+    @experimental
+    def sparkeySideInput(basePath: String, config: SparkeyReadConfig): SideInput[SparkeyReader] =
+      sparkeySideInputWithConfig(basePath, identity, config)
 
     /**
      * Create a SideInput of `TypedSparkeyReader` from a [[SparkeyUri]] base path, to be used with
@@ -152,14 +170,15 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
       decoder: Array[Byte] => T,
       cache: Cache[String, T] = null
     ): SideInput[TypedSparkeyReader[T]] =
-      sparkeySideInput(
+      sparkeySideInputWithConfig(
         basePath,
         reader =>
           new TypedSparkeyReader[T](
             reader,
             decoder,
             Option(cache).getOrElse(Cache.noOp[String, T])
-          )
+          ),
+        SparkeyReadConfig.Default
       )
 
     /**
@@ -171,7 +190,11 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
       basePath: String,
       cache: Cache[String, String]
     ): SideInput[CachedStringSparkeyReader] =
-      sparkeySideInput(basePath, reader => new CachedStringSparkeyReader(reader, cache))
+      sparkeySideInputWithConfig(
+        basePath,
+        reader => new CachedStringSparkeyReader(reader, cache),
+        SparkeyReadConfig.Default
+      )
   }
 
   /** Enhanced version of [[com.spotify.scio.values.SCollection SCollection]] with Sparkey methods. */
@@ -476,7 +499,11 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
      */
     @experimental
     def asSparkeySideInput: SideInput[SparkeyReader] =
-      new SparkeySideInput(self.applyInternal(View.asSingleton()), identity)
+      new SparkeySideInput(
+        self.applyInternal(View.asSingleton()),
+        identity,
+        SparkeyReadConfig.Default
+      )
 
     /**
      * Convert this SCollection to a SideInput of `SparkeyReader`, to be used with
@@ -490,7 +517,8 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
     ): SideInput[TypedSparkeyReader[T]] = {
       new SparkeySideInput(
         self.applyInternal(View.asSingleton()),
-        reader => new TypedSparkeyReader[T](reader, decoder, cache)
+        reader => new TypedSparkeyReader[T](reader, decoder, cache),
+        SparkeyReadConfig.Default
       )
     }
 
@@ -504,7 +532,8 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
     def asTypedSparkeySideInput[T](decoder: Array[Byte] => T): SideInput[TypedSparkeyReader[T]] =
       new SparkeySideInput(
         self.applyInternal(View.asSingleton()),
-        reader => new TypedSparkeyReader[T](reader, decoder, Cache.noOp)
+        reader => new TypedSparkeyReader[T](reader, decoder, Cache.noOp),
+        SparkeyReadConfig.Default
       )
 
     /**
@@ -517,7 +546,8 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
     ): SideInput[CachedStringSparkeyReader] =
       new SparkeySideInput(
         self.applyInternal(View.asSingleton()),
-        reader => new CachedStringSparkeyReader(reader, cache)
+        reader => new CachedStringSparkeyReader(reader, cache),
+        SparkeyReadConfig.Default
       )
   }
 
@@ -542,15 +572,19 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
 
   private class SparkeySideInput[T](
     val view: PCollectionView[SparkeyUri],
-    mapFn: SparkeyReader => T
+    mapFn: SparkeyReader => T,
+    config: SparkeyReadConfig
   ) extends SideInput[T] {
+    // Binary-compatible constructor (pre-3.6.1)
+    def this(view: PCollectionView[SparkeyUri], mapFn: SparkeyReader => T) =
+      this(view, mapFn, SparkeyReadConfig.Default)
     override def updateCacheOnGlobalWindow: Boolean = false
-    override def get[I, O](context: DoFn[I, O]#ProcessContext): T =
-      mapFn(
-        SparkeySideInput.checkMemory(
-          context.sideInput(view).getReader(RemoteFileUtil.create(context.getPipelineOptions))
-        )
-      )
+    override def get[I, O](context: DoFn[I, O]#ProcessContext): T = {
+      val uri = context.sideInput(view)
+      val rfu = RemoteFileUtil.create(context.getPipelineOptions)
+      val reader = SparkeySideInput.getOrCreateReader(uri, rfu, config)
+      mapFn(reader)
+    }
   }
 
   /**
@@ -585,6 +619,40 @@ package object sparkey extends SparkeyReaderInstances with SparkeyCoders {
 
   private object SparkeySideInput {
     private val logger = LoggerFactory.getLogger(this.getClass)
+
+    private val readerCache =
+      new java.util.concurrent.ConcurrentHashMap[
+        String,
+        java.util.concurrent.CompletableFuture[SparkeyReader]
+      ]()
+
+    def getOrCreateReader(
+      uri: SparkeyUri,
+      rfu: RemoteFileUtil,
+      config: SparkeyReadConfig
+    ): SparkeyReader = {
+      val future = readerCache.computeIfAbsent(
+        uri.path,
+        _ =>
+          // supplyAsync so computeIfAbsent returns quickly (it holds a bucket lock)
+          java.util.concurrent.CompletableFuture.supplyAsync { () =>
+            logger.info("Loading sparkey reader for {}", uri.path)
+            val reader = uri.getReader(rfu, config)
+            reader.load(config.loadMode)
+            checkMemory(reader)
+            reader
+          }
+      )
+      try {
+        future.get()
+      } catch {
+        case e: java.util.concurrent.ExecutionException =>
+          // Remove failed entry so next attempt can retry
+          readerCache.remove(uri.path, future)
+          throw e.getCause
+      }
+    }
+
     def checkMemory(reader: SparkeyReader): SparkeyReader = {
       val memoryBytes = java.lang.management.ManagementFactory.getOperatingSystemMXBean
         .asInstanceOf[com.sun.management.OperatingSystemMXBean]
diff --git a/scio-extra/src/test/scala/com/spotify/scio/extra/sparkey/SparkeyTest.scala b/scio-extra/src/test/scala/com/spotify/scio/extra/sparkey/SparkeyTest.scala
index a8a128f3dd..1c674534bb 100644
--- a/scio-extra/src/test/scala/com/spotify/scio/extra/sparkey/SparkeyTest.scala
+++ b/scio-extra/src/test/scala/com/spotify/scio/extra/sparkey/SparkeyTest.scala
@@ -639,4 +639,51 @@ class SparkeyTest extends PipelineSpec {
     result should contain theSameElementsAs expectedOutput
   }
 
+  it should "support heap budget for sharded sparkey" in {
+    val (_, sparkeyUris) = runWithLocalOutput(_.parallelize(bigSideData).asSparkey(numShards = 4))
+    val sparkeyUri = sparkeyUris.head
+    val rfu = RemoteFileUtil.create(PipelineOptionsFactory.create())
+
+    // With no heap budget (default) — all mmap
+    val defaultReader = sparkeyUri.getReader(rfu, SparkeyReadConfig())
+    defaultReader.toMap shouldBe bigSideData.toMap
+    defaultReader.close()
+
+    // With large heap budget — all shards on heap
+    val heapReader = sparkeyUri.getReader(rfu, SparkeyReadConfig(heapBudgetBytes = Long.MaxValue))
+    heapReader.toMap shouldBe bigSideData.toMap
+    bigSideData.foreach { case (k, v) =>
+      heapReader.getAsString(k) shouldBe v
+    }
+    heapReader.close()
+
+    // With tiny heap budget — only smallest shards fit
+    val tinyReader = sparkeyUri.getReader(rfu, SparkeyReadConfig(heapBudgetBytes = 1))
+    tinyReader.toMap shouldBe bigSideData.toMap
+    tinyReader.close()
+
+    FileUtils.deleteDirectory(new File(sparkeyUri.basePath))
+  }
+
+  it should "support heap budget for unsharded sparkey" in {
+    val (_, sparkeyUris) = runWithLocalOutput(_.parallelize(sideData).asSparkey)
+    val basePath = sparkeyUris.head.basePath
+    val sparkeyUri = SparkeyUri(basePath)
+    val rfu = RemoteFileUtil.create(PipelineOptionsFactory.create())
+
+    // Large budget — on heap
+    val heapReader = sparkeyUri.getReader(rfu, SparkeyReadConfig(heapBudgetBytes = Long.MaxValue))
+    heapReader.toMap shouldBe sideData.toMap
+    heapReader.close()
+
+    // Tiny budget — mmap
+    val mmapReader = sparkeyUri.getReader(rfu, SparkeyReadConfig(heapBudgetBytes = 1))
+    mmapReader.toMap shouldBe sideData.toMap
+    mmapReader.close()
+
+    for (ext <- Seq(".spi", ".spl")) {
+      new File(basePath + ext).delete()
+    }
+  }
+
 }