diff --git a/scripts/arcanist.php b/scripts/arcanist.php
index 785f4f8a..058fdedf 100755
--- a/scripts/arcanist.php
+++ b/scripts/arcanist.php
@@ -42,6 +42,7 @@ $argv = $args->getUnconsumedArgumentVector();
 $config_trace_mode = $args->getArg('trace');
 
 $force_conduit = null;
+$force_conduit_version = null;
 $args = $argv;
 $load = array();
 $matches = null;
@@ -54,6 +55,9 @@ foreach ($args as $key => $arg) {
   } else if (preg_match('/^--conduit-uri=(.*)$/', $arg, $matches)) {
     unset($args[$key]);
     $force_conduit = $matches[1];
+  } else if (preg_match('/^--conduit-version=(.*)$/', $arg, $matches)) {
+    unset($args[$key]);
+    $force_conduit_version = $matches[1];
   }
 }
 
@@ -193,6 +197,10 @@ try {
   $workflow->setWorkingDirectory($working_directory);
   $workflow->parseArguments($args);
 
+  if ($force_conduit_version) {
+    $workflow->forceConduitVersion($force_conduit_version);
+  }
+
   $need_working_copy    = $workflow->requiresWorkingCopy();
   $need_conduit         = $workflow->requiresConduit();
   $need_auth            = $workflow->requiresAuthentication();
diff --git a/src/workflow/base/ArcanistBaseWorkflow.php b/src/workflow/base/ArcanistBaseWorkflow.php
index e7cb4560..426631b1 100644
--- a/src/workflow/base/ArcanistBaseWorkflow.php
+++ b/src/workflow/base/ArcanistBaseWorkflow.php
@@ -56,6 +56,7 @@ abstract class ArcanistBaseWorkflow {
   private $conduitURI;
   private $conduitCredentials;
   private $conduitAuthenticated;
+  private $forcedConduitVersion;
 
   private $userPHID;
   private $userName;
@@ -178,6 +179,14 @@ abstract class ArcanistBaseWorkflow {
     return $this;
   }
 
+  public function forceConduitVersion($version) {
+    $this->forcedConduitVersion = $version;
+    return $this;
+  }
+
+  public function getConduitVersion() {
+    return nonempty($this->forcedConduitVersion, 5);
+  }
 
   /**
    * Open and authenticate a conduit connection to a Phabricator server using
@@ -234,7 +243,7 @@ abstract class ArcanistBaseWorkflow {
         'conduit.connect',
         array(
           'client'              => 'arc',
-          'clientVersion'       => 4,
+          'clientVersion'       => $this->getConduitVersion(),
           'clientDescription'   => php_uname('n').':'.$description,
           'user'                => $user,
           'certificate'         => $certificate,
diff --git a/src/workflow/help/ArcanistHelpWorkflow.php b/src/workflow/help/ArcanistHelpWorkflow.php
index 47de7394..a9c00b4c 100644
--- a/src/workflow/help/ArcanistHelpWorkflow.php
+++ b/src/workflow/help/ArcanistHelpWorkflow.php
@@ -199,6 +199,11 @@ EOTEXT
           Ignore configured Conduit URI and use an explicit one instead. Mostly
           useful for Arcanist development.
 
+      __--conduit-version=...__
+          Ignore software version and claim to be running some other version
+          instead. Mostly useful for Arcanist development. May cause bad things
+          to happen.
+
 
 EOTEXT
     );
diff --git a/src/workflow/upgrade/ArcanistUpgradeWorkflow.php b/src/workflow/upgrade/ArcanistUpgradeWorkflow.php
index 58b51353..d2ced0e1 100644
--- a/src/workflow/upgrade/ArcanistUpgradeWorkflow.php
+++ b/src/workflow/upgrade/ArcanistUpgradeWorkflow.php
@@ -33,7 +33,7 @@ EOTEXT
   public function getCommandHelp() {
     return phutil_console_format(<<<EOTEXT
           Supports: cli
-          Upgrade arc to the latest version.
+          Upgrade arcanist and libphutil to the latest versions.
 EOTEXT
       );
   }
@@ -43,38 +43,44 @@ EOTEXT
   }
 
   public function run() {
-    echo "Upgrading arc...\n";
-    $root = dirname(phutil_get_library_root('arcanist'));
+    $roots = array();
+    $roots['libphutil'] = dirname(phutil_get_library_root('phutil'));
+    $roots['arcanist'] = dirname(phutil_get_library_root('arcanist'));
 
-    if (!Filesystem::pathExists($root.'/.git')) {
-      throw new ArcanistUsageException(
-        "arc must be in its git working copy to be automatically upgraded. ".
-        "This copy of arc (in '{$root}') is not in a git working copy.");
-    }
+    foreach ($roots as $lib => $root) {
+      echo "Upgrading {$lib}...\n";
 
-    $working_copy = ArcanistWorkingCopyIdentity::newFromPath($root);
+      if (!Filesystem::pathExists($root.'/.git')) {
+        throw new ArcanistUsageException(
+          "{$lib} must be in its git working copy to be automatically ".
+          "upgraded. This copy of {$lib} (in '{$root}') is not in a git ".
+          "working copy.");
+      }
 
-    $repository_api = ArcanistRepositoryAPI::newAPIFromWorkingCopyIdentity(
-      $working_copy);
-    $this->setRepositoryAPI($repository_api);
+      $working_copy = ArcanistWorkingCopyIdentity::newFromPath($root);
 
-    // Require no local changes.
-    $this->requireCleanWorkingCopy();
+      $repository_api = ArcanistRepositoryAPI::newAPIFromWorkingCopyIdentity(
+        $working_copy);
+      $this->setRepositoryAPI($repository_api);
 
-    // Require arc be on master.
-    $branch_name = $repository_api->getBranchName();
-    if ($branch_name != 'master') {
-      throw new ArcanistUsageException(
-        "arc must be on branch 'master' to be automatically upgraded. ".
-        "This copy of arc (in '{$root}') is on branch '{$branch_name}'.");
-    }
+      // Require no local changes.
+      $this->requireCleanWorkingCopy();
 
-    chdir($root);
-    try {
-      phutil_passthru('git pull --rebase');
-    } catch (Exception $ex) {
-      phutil_passthru('git rebase --abort');
-      throw $ex;
+      // Require the library be on master.
+      $branch_name = $repository_api->getBranchName();
+      if ($branch_name != 'master') {
+        throw new ArcanistUsageException(
+          "{$lib} must be on branch 'master' to be automatically upgraded. ".
+          "This copy of {$lib} (in '{$root}') is on branch '{$branch_name}'.");
+      }
+
+      chdir($root);
+      try {
+        phutil_passthru('git pull --rebase');
+      } catch (Exception $ex) {
+        phutil_passthru('git rebase --abort');
+        throw $ex;
+      }
     }
 
     echo phutil_console_wrap(