diff --git a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/StashBufferSpec.scala b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/StashBufferSpec.scala
index 71e768b00a..9f648144df 100644
--- a/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/StashBufferSpec.scala
+++ b/akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/StashBufferSpec.scala
@@ -241,5 +241,11 @@ class StashBufferSpec extends AnyWordSpec with Matchers with LogCapturing {
       intercept[IllegalArgumentException](stash.unstashAll(Behaviors.unhandled))
     }
 
+    "answer thruthfully about its capacity" in {
+      val capacity = 42
+      val stash = StashBuffer[String](context, capacity)
+
+      stash.capacity should ===(capacity)
+    }
   }
 }
diff --git a/akka-actor-typed/src/main/mima-filters/2.6.3.backwards.excludes/pr-28739-expose-stashbuffer-capacity.excludes b/akka-actor-typed/src/main/mima-filters/2.6.3.backwards.excludes/pr-28739-expose-stashbuffer-capacity.excludes
new file mode 100644
index 0000000000..9fe23b3edc
--- /dev/null
+++ b/akka-actor-typed/src/main/mima-filters/2.6.3.backwards.excludes/pr-28739-expose-stashbuffer-capacity.excludes
@@ -0,0 +1,4 @@
+# https://github.com/akka/akka/pull/28739#issuecomment-602527515
+# StashBuffer trait is not meant to be extended by external users, and is marked as such with a @DoNotInherit
+ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.actor.typed.javadsl.StashBuffer.capacity")
+ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.actor.typed.scaladsl.StashBuffer.capacity")
\ No newline at end of file
diff --git a/akka-actor-typed/src/main/scala/akka/actor/typed/javadsl/StashBuffer.scala b/akka-actor-typed/src/main/scala/akka/actor/typed/javadsl/StashBuffer.scala
index 88a4534395..fac124ea41 100644
--- a/akka-actor-typed/src/main/scala/akka/actor/typed/javadsl/StashBuffer.scala
+++ b/akka-actor-typed/src/main/scala/akka/actor/typed/javadsl/StashBuffer.scala
@@ -42,6 +42,13 @@ import akka.japi.function.Procedure
    */
   def size: Int
 
+  /**
+   * What is the capacity of this buffer.
+   *
+   * @return the capacity of this buffer
+   */
+  def capacity: Int
+
   /**
    * @return `true` if no more messages can be added, i.e. size equals the capacity of the stash buffer
    */
diff --git a/akka-actor-typed/src/main/scala/akka/actor/typed/scaladsl/StashBuffer.scala b/akka-actor-typed/src/main/scala/akka/actor/typed/scaladsl/StashBuffer.scala
index 8f05a95e91..add12b5dac 100644
--- a/akka-actor-typed/src/main/scala/akka/actor/typed/scaladsl/StashBuffer.scala
+++ b/akka-actor-typed/src/main/scala/akka/actor/typed/scaladsl/StashBuffer.scala
@@ -55,6 +55,13 @@ import akka.annotation.{ DoNotInherit, InternalApi }
    */
   def size: Int
 
+  /**
+   * What is the capacity of this buffer.
+   *
+   * @return the capacity of this buffer
+   */
+  def capacity: Int
+
   /**
    * @return `true` if no more messages can be added, i.e. size equals the capacity of the stash buffer
    */