diff --git a/src/workflow/ArcanistWhichWorkflow.php b/src/workflow/ArcanistWhichWorkflow.php
--- a/src/workflow/ArcanistWhichWorkflow.php
+++ b/src/workflow/ArcanistWhichWorkflow.php
@@ -259,7 +259,7 @@
     $console = PhutilConsole::getConsole();
     $console->writeOut("**%s**\n", pht('REPOSITORY'));
 
-    $callsign = $this->getRepositoryCallsign();
+    $repo_name = $this->getRepositoryName();
 
     $console->writeOut(
       "%s\n\n",
@@ -272,11 +272,11 @@
       $console->writeOut("%s\n\n", $reason);
     }
 
-    if ($callsign) {
+    if ($repo_name) {
       $console->writeOut(
         "%s\n",
         pht('This working copy is associated with the %s repository.',
-        phutil_console_format('**%s**', $callsign)));
+        phutil_console_format('**%s**', $repo_name)));
     } else {
       $console->writeOut(
         "%s\n",
diff --git a/src/workflow/ArcanistWorkflow.php b/src/workflow/ArcanistWorkflow.php
--- a/src/workflow/ArcanistWorkflow.php
+++ b/src/workflow/ArcanistWorkflow.php
@@ -1107,8 +1107,17 @@
     // Don't amend the current commit if it has already been published.
     $repository = $this->loadProjectRepository();
     if ($repository) {
-      $callsign = $repository['callsign'];
-      $commit_name = 'r'.$callsign.$commit['commit'];
+      $repo_id = $repository['id'];
+      $commit_hash = $commit['commit'];
+      $callsign =  idx($repository, 'callsign');
+      if ($callsign) {
+        // The server might be too old to support the new style commit names,
+        // so prefer the old way
+        $commit_name = "r{$callsign}{$commit_hash}";
+      } else {
+        $commit_name = "R{$repo_id}:{$commit_hash}";
+      }
+
       $result = $this->getConduit()->callMethodSynchronous(
         'diffusion.querycommits',
         array('names' => array($commit_name)));
@@ -1686,18 +1695,17 @@
     return idx($this->getRepositoryInformation(), 'phid');
   }
 
-
   /**
-   * Get the callsign of the Phabricator repository this working copy
+   * Get the name of the Phabricator repository this working copy
    * corresponds to. Returns `null` if no repository can be identified.
    *
-   * @return string|null  Repository callsign, or null if no repository can be
+   * @return string|null  Repository name, or null if no repository can be
    *                      identified.
    *
    * @task phabrep
    */
-  final protected function getRepositoryCallsign() {
-    return idx($this->getRepositoryInformation(), 'callsign');
+  final protected function getRepositoryName() {
+    return idx($this->getRepositoryInformation(), 'name');
   }
 
 
@@ -2013,12 +2021,12 @@
     // If we know which repository we're in, try to tell Phabricator that we
     // pushed commits to it so it can update. This hint can help pull updates
     // more quickly, especially in rarely-used repositories.
-    if ($this->getRepositoryCallsign()) {
+    if ($this->getRepositoryPHID()) {
       try {
         $this->getConduit()->callMethodSynchronous(
           'diffusion.looksoon',
           array(
-            'callsigns' => array($this->getRepositoryCallsign()),
+            'repositories' => array($this->getRepositoryPHID()),
           ));
       } catch (ConduitClientException $ex) {
         // If we hit an exception, just ignore it. Likely, we are running