diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 7e7d87b05b..2ffc0c8a0c 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -122,6 +122,7 @@ phutil_register_library_map(array(
     'ConduitAPI_conpherence_createthread_Method' => 'applications/conpherence/conduit/ConduitAPI_conpherence_createthread_Method.php',
     'ConduitAPI_conpherence_querythread_Method' => 'applications/conpherence/conduit/ConduitAPI_conpherence_querythread_Method.php',
     'ConduitAPI_conpherence_querytransaction_Method' => 'applications/conpherence/conduit/ConduitAPI_conpherence_querytransaction_Method.php',
+    'ConduitAPI_conpherence_updatethread_Method' => 'applications/conpherence/conduit/ConduitAPI_conpherence_updatethread_Method.php',
     'ConduitAPI_daemon_launched_Method' => 'applications/daemon/conduit/ConduitAPI_daemon_launched_Method.php',
     'ConduitAPI_daemon_log_Method' => 'applications/daemon/conduit/ConduitAPI_daemon_log_Method.php',
     'ConduitAPI_daemon_setstatus_Method' => 'applications/daemon/conduit/ConduitAPI_daemon_setstatus_Method.php',
@@ -1963,6 +1964,7 @@ phutil_register_library_map(array(
     'ConduitAPI_conpherence_createthread_Method' => 'ConduitAPI_conpherence_Method',
     'ConduitAPI_conpherence_querythread_Method' => 'ConduitAPI_conpherence_Method',
     'ConduitAPI_conpherence_querytransaction_Method' => 'ConduitAPI_conpherence_Method',
+    'ConduitAPI_conpherence_updatethread_Method' => 'ConduitAPI_conpherence_Method',
     'ConduitAPI_daemon_launched_Method' => 'ConduitAPIMethod',
     'ConduitAPI_daemon_log_Method' => 'ConduitAPIMethod',
     'ConduitAPI_daemon_setstatus_Method' => 'ConduitAPIMethod',
diff --git a/src/applications/conpherence/conduit/ConduitAPI_conpherence_updatethread_Method.php b/src/applications/conpherence/conduit/ConduitAPI_conpherence_updatethread_Method.php
new file mode 100644
index 0000000000..9d2022f270
--- /dev/null
+++ b/src/applications/conpherence/conduit/ConduitAPI_conpherence_updatethread_Method.php
@@ -0,0 +1,104 @@
+<?php
+
+/**
+ * @group conduit
+ */
+final class ConduitAPI_conpherence_updatethread_Method
+  extends ConduitAPI_conpherence_Method {
+
+  public function getMethodDescription() {
+    return pht('Update an existing conpherence thread.');
+  }
+
+  public function defineParamTypes() {
+    return array(
+      'id' => 'optional int',
+      'phid' => 'optional phid',
+      'title' => 'optional string',
+      'message' => 'optional string',
+      'addParticipantPHIDs' => 'optional list<phids>',
+      'removeParticipantPHID' => 'optional phid'
+    );
+  }
+
+  public function defineReturnType() {
+    return 'bool';
+  }
+
+  public function defineErrorTypes() {
+    return array(
+      'ERR_USAGE_NO_THREAD_ID' => pht(
+        'You must specify a thread id or thread phid to query transactions '.
+        'from.'),
+      'ERR_USAGE_THREAD_NOT_FOUND' => pht(
+        'Thread does not exist or logged in user can not see it.'),
+      'ERR_USAGE_ONLY_SELF_REMOVE' => pht(
+        'Only a user can remove themselves from a thread.'),
+      'ERR_USAGE_NO_UPDATES' => pht(
+        'You must specify data that actually updates the conpherence.')
+    );
+  }
+
+  protected function execute(ConduitAPIRequest $request) {
+    $user = $request->getUser();
+    $id = $request->getValue('id');
+    $phid = $request->getValue('phid');
+    $query = id(new ConpherenceThreadQuery())
+      ->setViewer($user)
+      ->needFilePHIDs(true);
+    if ($id) {
+      $query->withIDs(array($id));
+    } else if ($phid) {
+      $query->withPHIDs(array($phid));
+    } else {
+      throw new ConduitException('ERR_USAGE_NO_THREAD_ID');
+    }
+    $conpherence = $query->executeOne();
+    if (!$conpherence) {
+      throw new ConduitException('ERR_USAGE_THREAD_NOT_FOUND');
+    }
+
+    $source = PhabricatorContentSource::newFromConduitRequest($request);
+    $editor = id(new ConpherenceEditor())
+      ->setContentSource($source)
+      ->setActor($user);
+    $xactions = array();
+    $add_participant_phids = $request->getValue('addParticipantPHIDs', array());
+    $remove_participant_phid = $request->getValue('removeParticipantPHID');
+    $message = $request->getValue('message');
+    $title = $request->getValue('title');
+    if ($add_participant_phids) {
+      $xactions[] = id(new ConpherenceTransaction())
+        ->setTransactionType(
+          ConpherenceTransactionType::TYPE_PARTICIPANTS)
+        ->setNewValue(array('+' => $add_participant_phids));
+    }
+    if ($remove_participant_phid) {
+      if ($remove_participant_phid != $user->getPHID()) {
+        throw new ConduitException('ERR_USAGE_ONLY_SELF_REMOVE');
+      }
+      $xactions[] = id(new ConpherenceTransaction())
+        ->setTransactionType(
+          ConpherenceTransactionType::TYPE_PARTICIPANTS)
+        ->setNewValue(array('-' => array($remove_participant_phid)));
+    }
+    if ($title) {
+      $xactions[] = id(new ConpherenceTransaction())
+        ->setTransactionType(ConpherenceTransactionType::TYPE_TITLE)
+        ->setNewValue($title);
+    }
+    if ($message) {
+      $xactions = array_merge(
+        $xactions,
+        $editor->generateTransactionsFromText($conpherence, $message));
+    }
+
+    try {
+      $xactions = $editor->applyTransactions($conpherence, $xactions);
+    } catch (PhabricatorApplicationTransactionNoEffectException $ex) {
+      throw new ConduitException('ERR_USAGE_NO_UPDATES');
+    }
+
+    return true;
+  }
+}