diff --git a/static/constants.json b/static/constants.json
index eacd93a66b..00afe20218 100644
--- a/static/constants.json
+++ b/static/constants.json
@@ -1415,26 +1415,20 @@
       "chevron-left",
       "triangle-left"
     ],
-    "BACK_BUTTON_SIZE_OPTIONS": [
-      "small",
-      "medium",
-      "large"
-    ],
-    "DEFAULT_BACK_BUTTON_DISPLAY": [
-      "none",
-      "flex"
-    ],
     "DEFAULT_BACK_BUTTON_ICON": "arrow-left",
-    "DEFAULT_BACK_BUTTON_SIZE": "medium",
     "DEFAULT_BREADCRUMBS_DISPLAY": [
       "none",
       "flex"
     ],
     "DEFAULT_CONTEXT_BAR_ACTIONS_DISPLAY": [
-      "block",
+      "flex",
       "none"
     ],
-    "DEFAULT_HEADER_VARIANT": "large",
+    "DEFAULT_HEADER_VARIANT": "medium",
+    "DEFAULT_LEADING_ACTION_DISPLAY": [
+      "none",
+      "flex"
+    ],
     "DEFAULT_PARENT_LINK_DISPLAY": [
       "block",
       "none"
@@ -1443,7 +1437,7 @@
       "medium",
       "large"
     ],
-    "HEADING_TAG_FALLBACK": "h2",
+    "HEADING_TAG_FALLBACK": "h1",
     "HEADING_TAG_OPTIONS": [
       "h1",
       "h2",
diff --git a/static/info_arch.json b/static/info_arch.json
index a49eb830c5..a47fecc77c 100644
--- a/static/info_arch.json
+++ b/static/info_arch.json
@@ -16178,20 +16178,14 @@
         ]
       },
       {
-        "name": "back_button",
-        "description": "Optional back button prepend the title\nBy default shown on wider screens. Can be overridden with system_argument: display",
+        "name": "leading_action",
+        "description": "Optional leading action prepend the title\nBy default shown on wider screens. Can be overridden with system_argument: display",
         "parameters": [
-          {
-            "name": "size",
-            "type": "Symbol",
-            "default": "N/A",
-            "description": "One of `:large`, `:medium`, or `:small`."
-          },
           {
             "name": "icon",
-            "type": "String",
+            "type": "Symbol",
             "default": "N/A",
-            "description": "One of `arrow-left`, `chevron-left`, or `triangle-left`."
+            "description": "The name of an {{link_to_octicons}} icon to use."
           },
           {
             "name": "system_arguments",
@@ -16276,8 +16270,8 @@
         }
       },
       {
-        "preview_path": "primer/open_project/page_header/medium_title",
-        "name": "medium_title",
+        "preview_path": "primer/open_project/page_header/large_title",
+        "name": "large_title",
         "snapshot": "false",
         "skip_rules": {
           "wont_fix": [
@@ -16302,8 +16296,8 @@
         }
       },
       {
-        "preview_path": "primer/open_project/page_header/back_button",
-        "name": "back_button",
+        "preview_path": "primer/open_project/page_header/leading_action",
+        "name": "leading_action",
         "snapshot": "false",
         "skip_rules": {
           "wont_fix": [
diff --git a/static/previews.json b/static/previews.json
index 6bd45eb41c..b116b9b46b 100644
--- a/static/previews.json
+++ b/static/previews.json
@@ -5028,8 +5028,8 @@
         }
       },
       {
-        "preview_path": "primer/open_project/page_header/medium_title",
-        "name": "medium_title",
+        "preview_path": "primer/open_project/page_header/large_title",
+        "name": "large_title",
         "snapshot": "false",
         "skip_rules": {
           "wont_fix": [
@@ -5054,8 +5054,8 @@
         }
       },
       {
-        "preview_path": "primer/open_project/page_header/back_button",
-        "name": "back_button",
+        "preview_path": "primer/open_project/page_header/leading_action",
+        "name": "leading_action",
         "snapshot": "false",
         "skip_rules": {
           "wont_fix": [