Index: resources/celerity/map.php
===================================================================
--- resources/celerity/map.php
+++ resources/celerity/map.php
@@ -10,7 +10,7 @@
     'core.pkg.css' => '607946ba',
     'core.pkg.js' => 'c7854cc5',
     'darkconsole.pkg.js' => 'ca8671ce',
-    'differential.pkg.css' => '5a65a762',
+    'differential.pkg.css' => '6aef439e',
     'differential.pkg.js' => '322ea941',
     'diffusion.pkg.css' => '3783278d',
     'diffusion.pkg.js' => '7b51e80a',
@@ -60,7 +60,6 @@
     'rsrc/css/application/differential/core.css' => '8135cb0c',
     'rsrc/css/application/differential/local-commits-view.css' => '19649019',
     'rsrc/css/application/differential/results-table.css' => '239924f9',
-    'rsrc/css/application/differential/revision-comment-list.css' => 'bc291c47',
     'rsrc/css/application/differential/revision-comment.css' => '48186045',
     'rsrc/css/application/differential/revision-history.css' => 'f37aee8f',
     'rsrc/css/application/differential/revision-list.css' => 'f3c47d33',
@@ -144,7 +143,7 @@
     'rsrc/css/phui/phui-status.css' => '2f562399',
     'rsrc/css/phui/phui-tag-view.css' => '295d81c4',
     'rsrc/css/phui/phui-text.css' => '23e9b4b7',
-    'rsrc/css/phui/phui-timeline-view.css' => '6c5e2da9',
+    'rsrc/css/phui/phui-timeline-view.css' => 'd3ccba00',
     'rsrc/css/phui/phui-workboard-view.css' => 'bf70dd2e',
     'rsrc/css/phui/phui-workpanel-view.css' => '6f8527f6',
     'rsrc/css/sprite-actions.css' => '4557baf8',
@@ -359,7 +358,7 @@
     'rsrc/js/application/differential/behavior-edit-inline-comments.js' => '93f43142',
     'rsrc/js/application/differential/behavior-keyboard-nav.js' => 'da3e88f9',
     'rsrc/js/application/differential/behavior-populate.js' => 'ce0c217a',
-    'rsrc/js/application/differential/behavior-show-all-comments.js' => '784b8218',
+    'rsrc/js/application/differential/behavior-show-all-comments.js' => '7c273581',
     'rsrc/js/application/differential/behavior-show-field-details.js' => '441f2137',
     'rsrc/js/application/differential/behavior-show-more.js' => 'dd7e8ef5',
     'rsrc/js/application/differential/behavior-toggle-files.js' => 'ca3f91eb',
@@ -508,7 +507,6 @@
     'differential-results-table-css' => '239924f9',
     'differential-revision-add-comment-css' => 'c478bcaa',
     'differential-revision-comment-css' => '48186045',
-    'differential-revision-comment-list-css' => 'bc291c47',
     'differential-revision-history-css' => 'f37aee8f',
     'differential-revision-list-css' => 'f3c47d33',
     'differential-table-of-contents-css' => '19566f76',
@@ -549,7 +547,6 @@
     'javelin-behavior-differential-feedback-preview' => '127f2018',
     'javelin-behavior-differential-keyboard-navigation' => 'da3e88f9',
     'javelin-behavior-differential-populate' => 'ce0c217a',
-    'javelin-behavior-differential-show-all-comments' => '784b8218',
     'javelin-behavior-differential-show-field-details' => '441f2137',
     'javelin-behavior-differential-show-more' => 'dd7e8ef5',
     'javelin-behavior-differential-toggle-files' => 'ca3f91eb',
@@ -598,6 +595,7 @@
     'javelin-behavior-phabricator-remarkup-assist' => 'c021950a',
     'javelin-behavior-phabricator-reveal-content' => '8f24abfc',
     'javelin-behavior-phabricator-search-typeahead' => 'f6b56f7a',
+    'javelin-behavior-phabricator-show-all-transactions' => '7c273581',
     'javelin-behavior-phabricator-tooltips' => 'e5dd1c6d',
     'javelin-behavior-phabricator-transaction-comment-form' => '9084a36f',
     'javelin-behavior-phabricator-transaction-list' => 'bfb45968',
@@ -756,7 +754,7 @@
     'phui-status-list-view-css' => '2f562399',
     'phui-tag-view-css' => '295d81c4',
     'phui-text-css' => '23e9b4b7',
-    'phui-timeline-view-css' => '6c5e2da9',
+    'phui-timeline-view-css' => 'd3ccba00',
     'phui-workboard-view-css' => 'bf70dd2e',
     'phui-workpanel-view-css' => '6f8527f6',
     'policy-css' => '957ea14c',
@@ -1235,12 +1233,6 @@
       0 => 'javelin-install',
       1 => 'javelin-util',
     ),
-    '784b8218' =>
-    array(
-      0 => 'javelin-behavior',
-      1 => 'javelin-stratcom',
-      2 => 'javelin-dom',
-    ),
     '79473b62' =>
     array(
       0 => 'javelin-install',
@@ -1256,6 +1248,12 @@
       1 => 'javelin-dom',
       2 => 'javelin-reactor-dom',
     ),
+    '7c273581' =>
+    array(
+      0 => 'javelin-behavior',
+      1 => 'javelin-stratcom',
+      2 => 'javelin-dom',
+    ),
     '7e41274a' =>
     array(
       0 => 'javelin-install',
@@ -2114,11 +2112,10 @@
       5 => 'differential-table-of-contents-css',
       6 => 'differential-revision-comment-css',
       7 => 'differential-revision-add-comment-css',
-      8 => 'differential-revision-comment-list-css',
-      9 => 'phabricator-object-selector-css',
-      10 => 'phabricator-content-source-view-css',
-      11 => 'differential-local-commits-view-css',
-      12 => 'inline-comment-summary-css',
+      8 => 'phabricator-object-selector-css',
+      9 => 'phabricator-content-source-view-css',
+      10 => 'differential-local-commits-view-css',
+      11 => 'inline-comment-summary-css',
     ),
     'differential.pkg.js' =>
     array(
Index: resources/celerity/packages.php
===================================================================
--- resources/celerity/packages.php
+++ resources/celerity/packages.php
@@ -124,7 +124,6 @@
     'differential-table-of-contents-css',
     'differential-revision-comment-css',
     'differential-revision-add-comment-css',
-    'differential-revision-comment-list-css',
     'phabricator-object-selector-css',
     'phabricator-content-source-view-css',
     'differential-local-commits-view-css',
Index: src/applications/transactions/view/PhabricatorApplicationTransactionView.php
===================================================================
--- src/applications/transactions/view/PhabricatorApplicationTransactionView.php
+++ src/applications/transactions/view/PhabricatorApplicationTransactionView.php
@@ -51,7 +51,7 @@
     return $this;
   }
 
-  public function buildEvents() {
+  public function buildEvents($with_hiding = false) {
     $user = $this->getUser();
 
     $anchor = $this->anchorOffset;
@@ -62,11 +62,50 @@
     $xactions = $this->groupRelatedTransactions($xactions);
     $groups = $this->groupDisplayTransactions($xactions);
 
+    // If the viewer has interacted with this object, we hide things from
+    // before their most recent interaction by default. This tends to make
+    // very long threads much more manageable, because you don't have to
+    // scroll through a lot of history and can focus on just new stuff.
+
+    $show_group = null;
+
+    if ($with_hiding) {
+      // Find the most recent comment by the viewer.
+      $group_keys = array_keys($groups);
+      $group_keys = array_reverse($group_keys);
+
+      // If we would only hide a small number of transactions, don't hide
+      // anything. Just don't examine the last few keys. Also, we always
+      // want to show the most recent pieces of activity, so don't examine
+      // the first few keys either.
+      $group_keys = array_slice($group_keys, 2, -2);
+
+      $type_comment = PhabricatorTransactions::TYPE_COMMENT;
+      foreach ($group_keys as $group_key) {
+        $group = $groups[$group_key];
+        foreach ($group as $xaction) {
+          if ($xaction->getAuthorPHID() == $user->getPHID() &&
+              $xaction->getTransactionType() == $type_comment) {
+            // This is the most recent group where the user commented.
+            $show_group = $group_key;
+            break 2;
+          }
+        }
+      }
+    }
+
     $events = array();
-    foreach ($groups as $group) {
+    $hide_by_default = ($show_group !== null);
+
+    foreach ($groups as $group_key => $group) {
+      if ($hide_by_default && ($show_group === $group_key)) {
+        $hide_by_default = false;
+      }
+
       $group_event = null;
       foreach ($group as $xaction) {
         $event = $this->renderEvent($xaction, $group, $anchor);
+        $event->setHideByDefault($hide_by_default);
         $anchor++;
         if (!$group_event) {
           $group_event = $event;
@@ -75,6 +114,7 @@
         }
       }
       $events[] = $group_event;
+
     }
 
     return $events;
@@ -86,7 +126,7 @@
     }
 
     $view = new PHUITimelineView();
-    $events = $this->buildEvents();
+    $events = $this->buildEvents($with_hiding = true);
     foreach ($events as $event) {
       $view->addEvent($event);
     }
Index: src/infrastructure/internationalization/translation/PhabricatorBaseEnglishTranslation.php
===================================================================
--- src/infrastructure/internationalization/translation/PhabricatorBaseEnglishTranslation.php
+++ src/infrastructure/internationalization/translation/PhabricatorBaseEnglishTranslation.php
@@ -826,6 +826,11 @@
         'users will need to sign again. Proceed carefully.',
       ),
 
+      '%s older changes(s) are hidden.' => array(
+        '%d older change is hidden.',
+        '%d older changes are hidden.',
+      ),
+
     );
   }
 
Index: src/view/phui/PHUITimelineEventView.php
===================================================================
--- src/view/phui/PHUITimelineEventView.php
+++ src/view/phui/PHUITimelineEventView.php
@@ -15,6 +15,16 @@
   private $transactionPHID;
   private $isPreview;
   private $eventGroup = array();
+  private $hideByDefault;
+
+  public function setHideByDefault($hide_by_default) {
+    $this->hideByDefault = $hide_by_default;
+    return $this;
+  }
+
+  public function getHideByDefault() {
+    return $this->hideByDefault;
+  }
 
   public function setTransactionPHID($transaction_phid) {
     $this->transactionPHID = $transaction_phid;
@@ -80,6 +90,10 @@
     return $this;
   }
 
+  public function getAnchor() {
+    return $this->anchor;
+  }
+
   public function setTitle($title) {
     $this->title = $title;
     return $this;
Index: src/view/phui/PHUITimelineView.php
===================================================================
--- src/view/phui/PHUITimelineView.php
+++ src/view/phui/PHUITimelineView.php
@@ -20,12 +20,74 @@
 
     $spacer = self::renderSpacer();
 
-    $events = array();
+    $hide = array();
+    $show = array();
+
     foreach ($this->events as $event) {
+      if ($event->getHideByDefault()) {
+        $hide[] = $event;
+      } else {
+        $show[] = $event;
+      }
+    }
+
+    $events = array();
+    if ($hide) {
+      $hidden = phutil_implode_html($spacer, $hide);
+      $count = count($hide);
+
+      $show_id = celerity_generate_unique_node_id();
+      $hide_id = celerity_generate_unique_node_id();
+      $link_id = celerity_generate_unique_node_id();
+
+      Javelin::initBehavior(
+        'phabricator-show-all-transactions',
+        array(
+          'anchors' => array_filter(mpull($hide, 'getAnchor')),
+          'linkID' => $link_id,
+          'hideID' => $hide_id,
+          'showID' => $show_id,
+        ));
+
+      $events[] = phutil_tag(
+        'div',
+        array(
+          'id' => $hide_id,
+          'class' => 'phui-timeline-older-transactions-are-hidden',
+        ),
+        array(
+          pht('%s older changes(s) are hidden.', new PhutilNumber($count)),
+          ' ',
+          javelin_tag(
+            'a',
+            array(
+              'href' => '#',
+              'mustcapture' => true,
+              'id' => $link_id,
+            ),
+            pht('Show all changes.')),
+        ));
+
+      $events[] = phutil_tag(
+        'div',
+        array(
+          'id' => $show_id,
+          'style' => 'display: none',
+        ),
+        $hidden);
+    }
+
+    if ($hide && $show) {
       $events[] = $spacer;
-      $events[] = $event;
     }
-    $events[] = $spacer;
+
+    if ($show) {
+      $events[] = phutil_implode_html($spacer, $show);
+    }
+
+    if ($events) {
+      $events = array($spacer, $events, $spacer);
+    }
 
     return phutil_tag(
       'div',
Index: webroot/rsrc/css/application/differential/revision-comment-list.css
===================================================================
--- webroot/rsrc/css/application/differential/revision-comment-list.css
+++ /dev/null
@@ -1,12 +0,0 @@
-/**
- * @provides differential-revision-comment-list-css
- */
-
-.differential-older-comments-are-hidden {
-  background: {$lightyellow};
-  border: 1px solid {$yellow};
-  text-align: center;
-  padding: 12px;
-  color: {$darkgreytext};
-  margin-top: 16px;
-}
Index: webroot/rsrc/css/phui/phui-timeline-view.css
===================================================================
--- webroot/rsrc/css/phui/phui-timeline-view.css
+++ webroot/rsrc/css/phui/phui-timeline-view.css
@@ -260,3 +260,12 @@
   border-color: #efefef;
   border-width: 1px 0;
 }
+
+.phui-timeline-older-transactions-are-hidden {
+  background: {$lightyellow};
+  border: 1px solid {$yellow};
+  text-align: center;
+  padding: 12px;
+  color: {$darkgreytext};
+  margin-top: 16px;
+}
Index: webroot/rsrc/js/application/differential/behavior-show-all-comments.js
===================================================================
--- webroot/rsrc/js/application/differential/behavior-show-all-comments.js
+++ webroot/rsrc/js/application/differential/behavior-show-all-comments.js
@@ -1,59 +1,66 @@
 /**
- * @provides javelin-behavior-differential-show-all-comments
+ * @provides javelin-behavior-phabricator-show-all-transactions
  * @requires javelin-behavior
  *           javelin-stratcom
  *           javelin-dom
  */
 
-JX.behavior('differential-show-all-comments', function(config) {
+/**
+ * Automatically show older transactions if the user follows an anchor to a
+ * transaction which is hidden by the "N older changes are hidden." shield.
+ */
+JX.behavior('phabricator-show-all-transactions', function(config) {
 
-  var shown = false;
-  function reveal(node) {
-    if (shown) {
-      return false;
-    }
-    shown = true;
-    node = node || JX.DOM.find(
-      document.body,
-      'div',
-      'differential-all-comments-container');
-    if (node) {
-      JX.DOM.setContent(node, JX.$H(config.markup));
+  var revealed = false;
+
+  function get_hash() {
+    return window.location.hash.replace(/^#/, '');
+  }
+
+  function hash_is_hidden() {
+    var hash = get_hash();
+    for (var ii = 0; ii < config.anchors.length; ii++) {
+      if (config.anchors[ii] == hash) {
+        return true;
+      }
     }
-    return true;
+    return false;
   }
 
-  // Reveal the hidden comments if the user clicks "Show All Comments", or if
-  // there's an anchor in the URL, since we don't want to link to "#comment-3"
-  // and have it collapsed.
+  function reveal() {
+    if (revealed) {
+      return false;
+    }
+
+    JX.DOM.hide(JX.$(config.hideID));
+    JX.DOM.show(JX.$(config.showID));
+    revealed = true;
 
-  function at_comment_hash() {
-    return window.location.hash && window.location.hash.match(/comment/);
+    return true;
   }
 
-  if (at_comment_hash()) {
-    reveal();
-  } else {
-    JX.Stratcom.listen(
-      'hashchange',
-      null,
-      function(e) {
-        if (at_comment_hash() && reveal()) {
-          try {
-            var target = JX.$(window.location.hash.replace(/^#/, ''));
-            window.scrollTo(0, target.offsetTop);
-          } catch (ex) {
-          }
+  function check_hash() {
+    if (hash_is_hidden()) {
+      if (reveal()) {
+        try {
+          var target = JX.$(get_hash());
+          JX.DOM.scrollTo(target);
+        } catch (ignored) {
+          // We did our best.
         }
-      });
+      }
+    }
   }
 
-  JX.Stratcom.listen(
+  JX.DOM.listen(
+    JX.$(config.linkID),
     'click',
-    'differential-show-all-comments',
-    function(e) {
-      reveal(e.getNode('differential-all-comments-container'));
+    null,
+    function (e) {
       e.kill();
+      reveal();
     });
 
+  JX.Stratcom.listen('hashchange', null, check_hash);
+  check_hash();
 });