diff --git a/main-command/src/main/scala/sbt/BasicCommandStrings.scala b/main-command/src/main/scala/sbt/BasicCommandStrings.scala
index d7da62d90..f7f728a38 100644
--- a/main-command/src/main/scala/sbt/BasicCommandStrings.scala
+++ b/main-command/src/main/scala/sbt/BasicCommandStrings.scala
@@ -194,6 +194,8 @@ $AliasCommand name=
 
   def Client = "client"
   def ClientDetailed = "Provides an interactive prompt from which commands can be run on a server."
+  def DashClient = "-client"
+  def DashDashClient = "--client"
 
   def StashOnFailure = "sbtStashOnFailure"
   def PopOnFailure = "sbtPopOnFailure"
diff --git a/main-command/src/main/scala/sbt/BasicCommands.scala b/main-command/src/main/scala/sbt/BasicCommands.scala
index 896cd9fe1..cc58497a6 100644
--- a/main-command/src/main/scala/sbt/BasicCommands.scala
+++ b/main-command/src/main/scala/sbt/BasicCommands.scala
@@ -297,7 +297,7 @@ object BasicCommands {
         case e :: Nil if e.commandLine == "shell" => Nil
         case xs                                   => xs map (_.commandLine)
       })
-    NetworkClient.run(arguments)
+    NetworkClient.run(s0.configuration.baseDirectory, arguments)
     "exit" :: s0.copy(remainingCommands = Nil)
   }
 
diff --git a/main-command/src/main/scala/sbt/CommandUtil.scala b/main-command/src/main/scala/sbt/CommandUtil.scala
index 4087b5932..6bdfcf0be 100644
--- a/main-command/src/main/scala/sbt/CommandUtil.scala
+++ b/main-command/src/main/scala/sbt/CommandUtil.scala
@@ -15,6 +15,7 @@ import sbt.internal.util.complete.Parser
 import sbt.internal.util.complete.DefaultParsers._
 
 import sbt.io.IO
+import sbt.io.syntax._
 
 object CommandUtil {
   def readLines(files: Seq[File]): Seq[String] =
@@ -89,4 +90,7 @@ object CommandUtil {
     details.map { case (k, v) => k + "\n\n  " + v } mkString ("\n", "\n\n", "\n")
 
   final val HelpPatternFlags = Pattern.CASE_INSENSITIVE | Pattern.UNICODE_CASE
+
+  private[sbt] def isSbtBuild(baseDir: File) =
+    (baseDir / "project").exists() || (baseDir * "*.sbt").get.nonEmpty
 }
diff --git a/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala b/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala
index 758f8712d..90ef086e3 100644
--- a/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala
+++ b/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala
@@ -24,7 +24,7 @@ import sbt.io.syntax._
 import sbt.io.IO
 import sjsonnew.support.scalajson.unsafe.Converter
 
-class NetworkClient(arguments: List[String]) { self =>
+class NetworkClient(baseDirectory: File, arguments: List[String]) { self =>
   private val channelName = new AtomicReference("_")
   private val status = new AtomicReference("Ready")
   private val lock: AnyRef = new AnyRef {}
@@ -39,7 +39,7 @@ class NetworkClient(arguments: List[String]) { self =>
 
   // Open server connection based on the portfile
   def init(): ServerConnection = {
-    val portfile = (file("project") / "target" / "active.json").getAbsoluteFile
+    val portfile = baseDirectory / "project" / "target" / "active.json"
     if (!portfile.exists) sys.error("server does not seem to be running.")
     val (sk, tkn) = ClientSocket.socket(portfile)
     val conn = new ServerConnection(sk) {
@@ -190,9 +190,9 @@ class NetworkClient(arguments: List[String]) { self =>
 }
 
 object NetworkClient {
-  def run(arguments: List[String]): Unit =
+  def run(baseDirectory: File, arguments: List[String]): Unit =
     try {
-      new NetworkClient(arguments)
+      new NetworkClient(baseDirectory, arguments)
       ()
     } catch {
       case NonFatal(e) => println(e.getMessage)
diff --git a/main/src/main/scala/sbt/Main.scala b/main/src/main/scala/sbt/Main.scala
index 49094156b..720d3c10d 100644
--- a/main/src/main/scala/sbt/Main.scala
+++ b/main/src/main/scala/sbt/Main.scala
@@ -64,15 +64,30 @@ import CommandStrings.BootCommand
 final class xMain extends xsbti.AppMain {
   def run(configuration: xsbti.AppConfiguration): xsbti.MainResult = {
     import BasicCommands.early
-    import BasicCommandStrings.runEarly
+    import BasicCommandStrings.{ runEarly, DashClient, DashDashClient }
     import BuiltinCommands.defaults
     import sbt.internal.CommandStrings.{ BootCommand, DefaultsCommand, InitCommand }
-    val state = StandardMain.initialState(
-      configuration,
-      Seq(defaults, early),
-      runEarly(DefaultsCommand) :: runEarly(InitCommand) :: BootCommand :: Nil
-    )
-    StandardMain.runManaged(state)
+    import sbt.internal.client.NetworkClient
+
+    // if we detect -Dsbt.client=true or -client, run thin client.
+    val clientModByEnv = java.lang.Boolean.getBoolean("sbt.client")
+    val userCommands = configuration.arguments.map(_.trim)
+    if (clientModByEnv || (userCommands.exists { cmd =>
+          (cmd == DashClient) || (cmd == DashDashClient)
+        })) {
+      val args = userCommands.toList filterNot { cmd =>
+        (cmd == DashClient) || (cmd == DashDashClient)
+      }
+      NetworkClient.run(configuration.baseDirectory, args)
+      Exit(0)
+    } else {
+      val state = StandardMain.initialState(
+        configuration,
+        Seq(defaults, early),
+        runEarly(DefaultsCommand) :: runEarly(InitCommand) :: BootCommand :: Nil
+      )
+      StandardMain.runManaged(state)
+    }
   }
 }
 
@@ -861,9 +876,6 @@ object BuiltinCommands {
   private val sbtVersionRegex = """sbt\.version\s*=.*""".r
   private def isSbtVersionLine(s: String) = sbtVersionRegex.pattern matcher s matches ()
 
-  private def isSbtProject(baseDir: File, projectDir: File) =
-    projectDir.exists() || (baseDir * "*.sbt").get.nonEmpty
-
   private def writeSbtVersionUnconditionally(state: State) = {
     val baseDir = state.baseDir
     val sbtVersion = BuiltinCommands.sbtVersion(state)
@@ -877,7 +889,7 @@ object BuiltinCommands {
     if (sbtVersionAbsent) {
       val warnMsg = s"No sbt.version set in project/build.properties, base directory: $baseDir"
       try {
-        if (isSbtProject(baseDir, projectDir)) {
+        if (isSbtBuild(baseDir)) {
           val line = s"sbt.version=$sbtVersion"
           IO.writeLines(buildProps, line :: buildPropsLines)
           state.log info s"Updated file $buildProps: set sbt.version to $sbtVersion"