diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index c00431caf..0c11909b6 100755
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -610,19 +610,30 @@ object Defaults extends BuildCommon {
     },
     externalHooks := {
       import sbt.nio.FileStamp.Formats.seqPathFileStampJsonFormatter
-      val current =
+      val currentInputs =
         (unmanagedSources / inputFileStamps).value ++ (managedSources / outputFileStamps).value
-      val previous = (externalHooks / inputFileStamps).previous
-      val changes = previous
-        .map(sbt.nio.Settings.changedFiles(_, current))
-        .getOrElse(FileChanges.noPrevious(current.map(_._1)))
-      ExternalHooks.default.value(changes, fileTreeView.value)
+      val previousInputs = (externalHooks / inputFileStamps).previous
+      val inputChanges = previousInputs
+        .map(sbt.nio.Settings.changedFiles(_, currentInputs))
+        .getOrElse(FileChanges.noPrevious(currentInputs.map(_._1)))
+      val currentOutputs = (dependencyClasspathFiles / outputFileStamps).value
+      val previousOutputs = (externalHooks / outputFileStamps).previous
+      val outputChanges = previousOutputs
+        .map(sbt.nio.Settings.changedFiles(_, currentOutputs))
+        .getOrElse(FileChanges.noPrevious(currentOutputs.map(_._1)))
+      ExternalHooks.default.value(inputChanges, outputChanges, fileTreeView.value)
     },
     externalHooks / inputFileStamps := {
       compile.value // ensures the inputFileStamps previous value is only set if compile succeeds.
       (unmanagedSources / inputFileStamps).value ++ (managedSources / outputFileStamps).value
     },
     externalHooks / inputFileStamps := (externalHooks / inputFileStamps).triggeredBy(compile).value,
+    externalHooks / outputFileStamps := {
+      compile.value // ensures the inputFileStamps previous value is only set if compile succeeds.
+      (dependencyClasspathFiles / outputFileStamps).value
+    },
+    externalHooks / outputFileStamps :=
+      (externalHooks / outputFileStamps).triggeredBy(compile).value,
     incOptions := { incOptions.value.withExternalHooks(externalHooks.value) },
     compileIncSetup := compileIncSetupTask.value,
     console := consoleTask.value,
@@ -2009,8 +2020,10 @@ object Classpaths {
         includeFilter in unmanagedJars value,
         excludeFilter in unmanagedJars value
       )
-    ).map(exportClasspath) :+
-      (sbt.nio.Keys.classpathFiles := data(fullClasspath.value).map(_.toPath))
+    ).map(exportClasspath) ++ Seq(
+      sbt.nio.Keys.classpathFiles := data(fullClasspath.value).map(_.toPath),
+      sbt.nio.Keys.dependencyClasspathFiles := data(dependencyClasspath.value).map(_.toPath),
+    )
 
   private[this] def exportClasspath(s: Setting[Task[Classpath]]): Setting[Task[Classpath]] =
     s.mapInitialize(init => Def.task { exportClasspath(streams.value, init.value) })
diff --git a/main/src/main/scala/sbt/internal/ExternalHooks.scala b/main/src/main/scala/sbt/internal/ExternalHooks.scala
index 269a249f4..97c495ab5 100644
--- a/main/src/main/scala/sbt/internal/ExternalHooks.scala
+++ b/main/src/main/scala/sbt/internal/ExternalHooks.scala
@@ -26,7 +26,8 @@ import scala.collection.JavaConverters._
 
 private[sbt] object ExternalHooks {
   private val javaHome = Option(System.getProperty("java.home")).map(Paths.get(_))
-  private type Func = (FileChanges, FileTreeView[(Path, FileAttributes)]) => ExternalHooks
+  private type Func =
+    (FileChanges, FileChanges, FileTreeView[(Path, FileAttributes)]) => ExternalHooks
   def default: Def.Initialize[sbt.Task[Func]] = Def.task {
     val unmanagedCache = unmanagedFileStampCache.value
     val managedCache = managedFileStampCache.value
@@ -37,15 +38,16 @@ private[sbt] object ExternalHooks {
     }
     val classGlob = classDirectory.value.toGlob / RecursiveGlob / "*.class"
     val options = (compileOptions in compile).value
-    (fc: FileChanges, fileTreeView: FileTreeView[(Path, FileAttributes)]) => {
+    ((inputFileChanges, outputFileChanges, fileTreeView) => {
       fileTreeView.list(classGlob).foreach {
         case (path, _) => managedCache.update(path, FileStamper.LastModified)
       }
-      apply(fc, options, unmanagedCache, managedCache)
-    }
+      apply(inputFileChanges, outputFileChanges, options, unmanagedCache, managedCache)
+    }): Func
   }
   private def apply(
-      changedFiles: FileChanges,
+      inputFileChanges: FileChanges,
+      outputFileChanges: FileChanges,
       options: CompileOptions,
       unmanagedCache: FileStamp.Cache,
       managedCache: FileStamp.Cache
@@ -62,7 +64,7 @@ private[sbt] object ExternalHooks {
           }
           private def add(f: File, set: java.util.Set[File]): Unit = { set.add(f); () }
           val allChanges = new java.util.HashSet[File]
-          changedFiles match {
+          inputFileChanges match {
             case FileChanges(c, d, m, _) =>
               c.foreach(add(_, getAdded, allChanges))
               d.foreach(add(_, getRemoved, allChanges))
@@ -99,9 +101,13 @@ private[sbt] object ExternalHooks {
         Optional.empty[Array[FileHash]]
 
       override def changedBinaries(previousAnalysis: CompileAnalysis): Option[Set[File]] = {
-        Some(previousAnalysis.readStamps.getAllBinaryStamps.asScala.flatMap {
+        val base =
+          (outputFileChanges.modified ++ outputFileChanges.created ++ outputFileChanges.deleted)
+            .map(_.toFile)
+            .toSet
+        Some(base ++ previousAnalysis.readStamps.getAllBinaryStamps.asScala.flatMap {
           case (file, stamp) =>
-            managedCache.get(file.toPath) match {
+            managedCache.getOrElseUpdate(file.toPath, FileStamper.LastModified) match {
               case Some(cachedStamp) if equiv(cachedStamp.stamp, stamp) => None
               case _ =>
                 javaHome match {
@@ -110,7 +116,7 @@ private[sbt] object ExternalHooks {
                   case _                                    => Some(file)
                 }
             }
-        }.toSet)
+        })
       }
 
       override def removedProducts(previousAnalysis: CompileAnalysis): Option[Set[File]] = {
diff --git a/main/src/main/scala/sbt/nio/Keys.scala b/main/src/main/scala/sbt/nio/Keys.scala
index 32b61b0bd..918641c51 100644
--- a/main/src/main/scala/sbt/nio/Keys.scala
+++ b/main/src/main/scala/sbt/nio/Keys.scala
@@ -160,6 +160,8 @@ object Keys {
   private[sbt] val managedFileStampCache = taskKey[FileStamp.Cache](
     "Map of managed file stamps that may be cleared between task evaluation runs."
   ).withRank(Invisible)
+  private[sbt] val dependencyClasspathFiles =
+    taskKey[Seq[Path]]("The dependency classpath for a task.").withRank(Invisible)
   private[sbt] val classpathFiles =
     taskKey[Seq[Path]]("The classpath for a task.").withRank(Invisible)
 
diff --git a/main/src/main/scala/sbt/nio/Settings.scala b/main/src/main/scala/sbt/nio/Settings.scala
index 1f22d406f..bc54946ba 100644
--- a/main/src/main/scala/sbt/nio/Settings.scala
+++ b/main/src/main/scala/sbt/nio/Settings.scala
@@ -242,12 +242,12 @@ private[sbt] object Settings {
     }
     prevMap.forEach((p, _) => deletedBuilder += p)
     val unmodified = unmodifiedBuilder.result()
-    if (unmodified.size == current.size) {
+    val deleted = deletedBuilder.result()
+    val created = createdBuilder.result()
+    val modified = modifiedBuilder.result()
+    if (created.isEmpty && deleted.isEmpty && modified.isEmpty) {
       FileChanges.unmodified(unmodifiedBuilder.result)
     } else {
-      val created = createdBuilder.result()
-      val deleted = deletedBuilder.result()
-      val modified = modifiedBuilder.result()
       FileChanges(created, deleted, modified, unmodified)
     }
   }