Play 2.5 使用的 Akka Streams 是什么版本？

What is the version of Akka Streams that Play 2.5 uses?

From version 2.5, Play’s default stream processing library is Akka Streams.

我在任何地方都找不到官方文档，我想知道 Play 2.5 使用的 Akka Stream 版本到底是什么？

Play 2.5.x uses Akka 2.4.20:

object Dependencies {

  val akkaVersion = "2.4.20"
  ...
  val streamsDependencies = Seq(
    "org.reactivestreams" % "reactive-streams" % "1.0.0",
    "com.typesafe.akka" %% "akka-stream" % akkaVersion,
  ...
}