diff --git a/tildes/scss/modules/_comment.scss b/tildes/scss/modules/_comment.scss
index cf5d5c0..93db50b 100644
--- a/tildes/scss/modules/_comment.scss
+++ b/tildes/scss/modules/_comment.scss
@@ -142,6 +142,14 @@
   }
 }
 
+// uses @extend to only collapse everything inside the collapsed comment itself and
+// not its replies
+.is-comment-collapsed-individual {
+  & > .comment-itself {
+    @extend .is-comment-collapsed;
+  }
+}
+
 .is-comment-deleted, .is-comment-removed {
   font-size: 0.7rem;
   font-style: italic;
diff --git a/tildes/static/js/behaviors/comment-collapse-all-button.js b/tildes/static/js/behaviors/comment-collapse-all-button.js
index 64827a5..d90190b 100644
--- a/tildes/static/js/behaviors/comment-collapse-all-button.js
+++ b/tildes/static/js/behaviors/comment-collapse-all-button.js
@@ -1,5 +1,13 @@
 $.onmount('[data-js-comment-collapse-all-button]', function() {
     $(this).click(function(event) {
+        // first uncollapse any individually collapsed comments
+        $('.is-comment-collapsed-individual').each(
+            function(idx, child) {
+                $(child).find(
+                    '[data-js-comment-collapse-button]:first').trigger('click');
+            });
+
+        // then collapse all first-level replies
         $('.comment[data-comment-depth="1"]:not(.is-comment-collapsed)').each(
             function(idx, child) {
                 $(child).find(
diff --git a/tildes/static/js/behaviors/comment-collapse-button.js b/tildes/static/js/behaviors/comment-collapse-button.js
index 4edd188..f277838 100644
--- a/tildes/static/js/behaviors/comment-collapse-button.js
+++ b/tildes/static/js/behaviors/comment-collapse-button.js
@@ -3,7 +3,13 @@ $.onmount('[data-js-comment-collapse-button]', function() {
         $this = $(this);
         $comment = $this.closest('.comment');
 
-        $comment.toggleClass('is-comment-collapsed');
+        // if the comment is individually collapsed, just remove that class,
+        // otherwise toggle the collapsed state
+        if ($comment.hasClass('is-comment-collapsed-individual')) {
+            $comment.removeClass('is-comment-collapsed-individual');
+        } else {
+            $comment.toggleClass('is-comment-collapsed');
+        }
 
         if ($comment.hasClass('is-comment-collapsed')) {
             $this.text('+');
diff --git a/tildes/static/js/behaviors/comment-expand-all-button.js b/tildes/static/js/behaviors/comment-expand-all-button.js
index f870139..53c5ce5 100644
--- a/tildes/static/js/behaviors/comment-expand-all-button.js
+++ b/tildes/static/js/behaviors/comment-expand-all-button.js
@@ -1,6 +1,6 @@
 $.onmount('[data-js-comment-expand-all-button]', function() {
     $(this).click(function(event) {
-        $('.comment.is-comment-collapsed').each(
+        $('.is-comment-collapsed, .is-comment-collapsed-individual').each(
             function(idx, child) {
                 $(child).find(
                     '[data-js-comment-collapse-button]:first').trigger('click');
diff --git a/tildes/tildes/jinja.py b/tildes/tildes/jinja.py
index 227404a..1b5f3ed 100644
--- a/tildes/tildes/jinja.py
+++ b/tildes/tildes/jinja.py
@@ -31,7 +31,6 @@ def includeme(config: Configurator) -> None:
 
     settings["jinja2.lstrip_blocks"] = True
     settings["jinja2.trim_blocks"] = True
-    settings["jinja2.undefined"] = "strict"
 
     # add custom jinja filters
     settings["jinja2.filters"] = {"ago": descriptive_timedelta}
diff --git a/tildes/tildes/models/comment/comment_tree.py b/tildes/tildes/models/comment/comment_tree.py
index b04fdd7..b4299f6 100644
--- a/tildes/tildes/models/comment/comment_tree.py
+++ b/tildes/tildes/models/comment/comment_tree.py
@@ -1,5 +1,6 @@
 """Contains the CommentTree class."""
 
+from datetime import datetime
 from typing import Iterator, List, Optional, Sequence
 
 from prometheus_client import Histogram
@@ -16,6 +17,7 @@ class CommentTree:
         - `replies`: the list of all immediate children to that comment
         - `has_visible_descendant`: whether the comment has any visible descendants (if
           not, it can be pruned from the tree)
+        - `collapsed_state`: whether to display this comment in a collapsed state
     """
 
     def __init__(self, comments: Sequence[Comment], sort: CommentSortOption) -> None:
@@ -27,6 +29,11 @@ class CommentTree:
         # ensure that parent comments are always processed first
         self.comments = sorted(comments, key=lambda c: c.created_time)
 
+        for comment in self.comments:
+            comment.collapsed_state = None
+
+        self.comments_by_id = {comment.comment_id: comment for comment in comments}
+
         # if there aren't any comments, we can just bail out here
         if not self.comments:
             return
@@ -45,15 +52,12 @@ class CommentTree:
 
     def _build_tree(self) -> None:
         """Build the initial tree from the flat list of Comments."""
-        comments_by_id = {}
-
         for comment in self.comments:
             comment.replies = []
             comment.has_visible_descendant = False
-            comments_by_id[comment.comment_id] = comment
 
             if comment.parent_comment_id:
-                parent_comment = comments_by_id[comment.parent_comment_id]
+                parent_comment = self.comments_by_id[comment.parent_comment_id]
                 parent_comment.replies.append(comment)
 
                 # if this comment isn't deleted, work back up towards the root,
@@ -66,7 +70,7 @@ class CommentTree:
                             break
 
                         next_parent_id = parent_comment.parent_comment_id
-                        parent_comment = comments_by_id[next_parent_id]
+                        parent_comment = self.comments_by_id[next_parent_id]
             else:
                 self.tree.append(comment)
 
@@ -156,3 +160,61 @@ class CommentTree:
             num_comments_range=num_comments_range,
             order=self.sort.name,
         )
+
+    def collapse_old_comments(self, threshold: datetime) -> None:
+        """Collapse old comments in the tree.
+
+        Any comments newer than the threshold will be uncollapsed, along with their
+        direct parents. All comments with any uncollapsed descendant will be collapsed
+        individually. Branches with no uncollapsed comments will be collapsed fully.
+        """
+        for comment in reversed(self.comments):
+            # as soon as we reach an old comment, we can stop
+            if comment.created_time <= threshold:
+                break
+
+            if comment.is_deleted or comment.is_removed:
+                continue
+
+            # uncollapse the comment
+            comment.collapsed_state = "uncollapsed"
+
+            # fetch its direct parent and uncollapse it as well
+            parent_comment: Optional[Comment] = None
+            if comment.parent_comment_id:
+                parent_comment = self.comments_by_id[comment.parent_comment_id]
+                parent_comment.collapsed_state = "uncollapsed"
+
+            # then follow parents to the root, individually collapsing them all
+            while parent_comment:
+                if not parent_comment.collapsed_state:
+                    parent_comment.collapsed_state = "individual"
+
+                if parent_comment.parent_comment_id:
+                    parent_comment = self.comments_by_id[
+                        parent_comment.parent_comment_id
+                    ]
+                else:
+                    parent_comment = None
+
+        self._finalize_collapsing()
+
+    def _finalize_collapsing(self) -> None:
+        """Finish collapsing that was done partially by a different method."""
+        # if all the comments would end up collapsed, leave them all uncollapsed
+        if all([comment.collapsed_state is None for comment in self.comments]):
+            return
+
+        # go over each top-level comment and go into each branch depth-first. Any
+        # comment that still has its state as None can be fully collapsed (and we can
+        # stop looking down that branch)
+        def recursively_collapse(comment: Comment) -> None:
+            if not comment.collapsed_state:
+                comment.collapsed_state = "full"
+                return
+
+            for reply in comment.replies:
+                recursively_collapse(reply)
+
+        for comment in self.tree:
+            recursively_collapse(comment)
diff --git a/tildes/tildes/templates/macros/comments.jinja2 b/tildes/tildes/templates/macros/comments.jinja2
index 52dfe3d..6e6d5ea 100644
--- a/tildes/tildes/templates/macros/comments.jinja2
+++ b/tildes/tildes/templates/macros/comments.jinja2
@@ -35,7 +35,9 @@
 {% macro render_comment_contents(comment, is_individual_comment=False) %}
   <div class="comment-itself">
     <header>
-      <button class="btn btn-comment-collapse" data-js-comment-collapse-button>&minus;</button>
+      <button class="btn btn-comment-collapse" data-js-comment-collapse-button>
+        {{ "+" if comment.collapsed_state in ("full", "individual") else "−" }}
+      </button>
 
       {% if request.has_permission('view', comment) %}
         {{ username_linked(comment.user.username) }}
@@ -206,6 +208,12 @@
     {% elif request.has_permission('view_author', comment.topic) and comment.user == comment.topic.user %}
       {% do classes.append('is-comment-by-op') %}
     {% endif %}
+
+    {% if comment.collapsed_state == "full" %}
+      {% do classes.append("is-comment-collapsed") %}
+    {% elif comment.collapsed_state == "individual" %}
+      {% do classes.append("is-comment-collapsed-individual") %}
+    {% endif %}
   {% endif %}
 
   {{ classes|join(' ') }}
diff --git a/tildes/tildes/views/topic.py b/tildes/tildes/views/topic.py
index 7f2e53f..8cf9d4d 100644
--- a/tildes/tildes/views/topic.py
+++ b/tildes/tildes/views/topic.py
@@ -272,13 +272,17 @@ def get_topic(request: Request, comment_order: CommentSortOption) -> dict:
         .all()
     )
 
-    # if the feature's enabled, update their last visit to this topic
+    # if the user has the "mark new comments" feature enabled
     if request.user and request.user.track_comment_visits:
+        # update their last visit time for this topic
         statement = TopicVisit.generate_insert_statement(request.user, topic)
-
         request.db_session.execute(statement)
         mark_changed(request.db_session)
 
+        # collapse old comments if the user has a previous visit to the topic
+        if topic.last_visit_time:
+            tree.collapse_old_comments(topic.last_visit_time)
+
     return {
         "topic": topic,
         "log": log,