diff --git a/scripts/startup/bl_ui/space_dopesheet.py b/scripts/startup/bl_ui/space_dopesheet.py
index d852ba8e13f..5fcb64b08f8 100644
--- a/scripts/startup/bl_ui/space_dopesheet.py
+++ b/scripts/startup/bl_ui/space_dopesheet.py
@@ -205,16 +205,10 @@ class DOPESHEET_HT_header(Header):
         st = context.space_data
 
         layout.template_header()
+        layout.prop(st, "ui_mode", text="")
 
-        if st.mode == 'TIMELINE':
-            from bl_ui.space_time import TIME_MT_editor_menus
-            TIME_MT_editor_menus.draw_collapsible(context, layout)
-            playback_controls(layout, context)
-        else:
-            layout.prop(st, "ui_mode", text="")
-
-            DOPESHEET_MT_editor_menus.draw_collapsible(context, layout)
-            DOPESHEET_HT_editor_buttons.draw_header(context, layout)
+        DOPESHEET_MT_editor_menus.draw_collapsible(context, layout)
+        DOPESHEET_HT_editor_buttons.draw_header(context, layout)
 
 
 # Header for "normal" dopesheet editor modes (e.g. Dope Sheet, Action, Shape Keys, etc.)
diff --git a/scripts/startup/bl_ui/space_time.py b/scripts/startup/bl_ui/space_time.py
index 9f4b0f66ea0..bb055ac1f53 100644
--- a/scripts/startup/bl_ui/space_time.py
+++ b/scripts/startup/bl_ui/space_time.py
@@ -126,71 +126,6 @@ def playback_controls(layout, context):
             sub.prop(scene, "frame_preview_end", text="End")
 
 
-class TIME_MT_editor_menus(Menu):
-    bl_idname = "TIME_MT_editor_menus"
-    bl_label = ""
-
-    def draw(self, context):
-        layout = self.layout
-        horizontal = (layout.direction == 'VERTICAL')
-        st = context.space_data
-        if horizontal:
-            row = layout.row()
-            sub = row.row(align=True)
-        else:
-            sub = layout
-
-        sub.menu("TIME_MT_view")
-        if st.show_markers:
-            sub.menu("TIME_MT_marker")
-
-
-class TIME_MT_marker(Menu):
-    bl_label = "Marker"
-
-    def draw(self, context):
-        layout = self.layout
-
-        marker_menu_generic(layout, context)
-
-
-class TIME_MT_view(Menu):
-    bl_label = "View"
-
-    def draw(self, context):
-        layout = self.layout
-
-        scene = context.scene
-        st = context.space_data
-
-        layout.prop(st, "show_region_hud")
-        layout.prop(st, "show_region_channels")
-        layout.separator()
-
-        # NOTE: "action" now, since timeline is in the dopesheet editor, instead of as own editor
-        layout.operator("action.view_all")
-        if context.scene.use_preview_range:
-            layout.operator("anim.scene_range_frame", text="Frame Preview Range")
-        else:
-            layout.operator("anim.scene_range_frame", text="Frame Scene Range")
-        layout.operator("action.view_frame")
-        layout.separator()
-
-        layout.prop(st, "show_markers")
-        layout.prop(st, "show_seconds")
-        layout.prop(st, "show_locked_time")
-        layout.separator()
-
-        layout.prop(scene, "show_keys_from_selected_only")
-        layout.prop(st.dopesheet, "show_only_errors")
-        layout.separator()
-
-        layout.menu("DOPESHEET_MT_cache")
-        layout.separator()
-
-        layout.menu("INFO_MT_area")
-
-
 def marker_menu_generic(layout, context):
 
     # layout.operator_context = 'EXEC_REGION_WIN'
@@ -357,9 +292,6 @@ class TIME_PT_auto_keyframing(TimelinePanelButtons, Panel):
 ###################################
 
 classes = (
-    TIME_MT_editor_menus,
-    TIME_MT_marker,
-    TIME_MT_view,
     TIME_PT_playback,
     TIME_PT_keyframing_settings,
     TIME_PT_auto_keyframing,
diff --git a/source/blender/blenkernel/BKE_blender_version.h b/source/blender/blenkernel/BKE_blender_version.h
index 7b810a88d15..427e9178fd4 100644
--- a/source/blender/blenkernel/BKE_blender_version.h
+++ b/source/blender/blenkernel/BKE_blender_version.h
@@ -27,7 +27,7 @@
 
 /* Blender file format version. */
 #define BLENDER_FILE_VERSION BLENDER_VERSION
-#define BLENDER_FILE_SUBVERSION 99
+#define BLENDER_FILE_SUBVERSION 100
 
 /* Minimum Blender version that supports reading file written with the current
  * version. Older Blender versions will test this and cancel loading the file, showing a warning to
diff --git a/source/blender/blenloader/intern/versioning_500.cc b/source/blender/blenloader/intern/versioning_500.cc
index 41c9bbc0e73..f2238ff0804 100644
--- a/source/blender/blenloader/intern/versioning_500.cc
+++ b/source/blender/blenloader/intern/versioning_500.cc
@@ -3778,6 +3778,35 @@ void blo_do_versions_500(FileData *fd, Library * /*lib*/, Main *bmain)
     }
   }
 
+  if (!MAIN_VERSION_FILE_ATLEAST(bmain, 500, 100)) {
+    LISTBASE_FOREACH (bScreen *, screen, &bmain->screens) {
+      LISTBASE_FOREACH (ScrArea *, area, &screen->areabase) {
+        LISTBASE_FOREACH (SpaceLink *, sl, &area->spacedata) {
+          if (!ELEM(sl->spacetype, SPACE_ACTION)) {
+            continue;
+          }
+          SpaceAction *saction = reinterpret_cast<SpaceAction *>(sl);
+          if (saction->mode != SACTCONT_TIMELINE) {
+            continue;
+          }
+          /* Switching to dopesheet since that is the closest to the timeline view. */
+          saction->mode = SACTCONT_DOPESHEET;
+          /* The multiplication by 2 assumes that the time control footer has the same size as the
+           * header. The header is only shown if there is enough space for both. */
+          const bool show_header = area->winy > (HEADERY * UI_SCALE_FAC) * 2;
+          LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
+            if (!show_header && region->regiontype == RGN_TYPE_HEADER) {
+              region->flag |= RGN_FLAG_HIDDEN;
+            }
+            if (region->regiontype == RGN_TYPE_FOOTER) {
+              region->flag &= ~RGN_FLAG_HIDDEN;
+            }
+          }
+        }
+      }
+    }
+  }
+
   /**
    * Always bump subversion in BKE_blender_version.h when adding versioning
    * code here, and wrap it inside a MAIN_VERSION_FILE_ATLEAST check.
diff --git a/source/blender/editors/animation/anim_filter.cc b/source/blender/editors/animation/anim_filter.cc
index 17436d39f00..a33b1127c13 100644
--- a/source/blender/editors/animation/anim_filter.cc
+++ b/source/blender/editors/animation/anim_filter.cc
@@ -140,11 +140,13 @@ bAction *ANIM_active_action_from_area(Scene *scene,
     case SACTCONT_DOPESHEET:
     case SACTCONT_MASK:
     case SACTCONT_CACHEFILE:
-    case SACTCONT_TIMELINE:
       if (r_action_user) {
         *r_action_user = nullptr;
       }
       return nullptr;
+    case SACTCONT_TIMELINE:
+      BLI_assert_unreachable();
+      break;
   }
 
   BLI_assert_unreachable();
@@ -247,29 +249,6 @@ static bool actedit_get_context(bAnimContext *ac, SpaceAction *saction)
       ac->data = &saction->ads;
       return true;
 
-    case SACTCONT_TIMELINE: /* Timeline */
-      /* update scene-pointer (no need to check for pinning yet, as not implemented) */
-      saction->ads.source = reinterpret_cast<ID *>(ac->scene);
-
-      /* sync scene's "selected keys only" flag with our "only selected" flag
-       *
-       * XXX: This is a workaround for #55525. We shouldn't really be syncing the flags like this,
-       * but it's a simpler fix for now than also figuring out how the next/prev keyframe
-       * tools should work in the 3D View if we allowed full access to the timeline's
-       * dopesheet filters (i.e. we'd have to figure out where to host those settings,
-       * to be on a scene level like this flag currently is, along with several other unknowns).
-       */
-      if (ac->scene->flag & SCE_KEYS_NO_SELONLY) {
-        saction->ads.filterflag &= ~ADS_FILTER_ONLYSEL;
-      }
-      else {
-        saction->ads.filterflag |= ADS_FILTER_ONLYSEL;
-      }
-
-      ac->datatype = ANIMCONT_TIMELINE;
-      ac->data = &saction->ads;
-      return true;
-
     default: /* unhandled yet */
       ac->datatype = ANIMCONT_NONE;
       ac->data = nullptr;
diff --git a/source/blender/editors/interface/templates/interface_template_search_menu.cc b/source/blender/editors/interface/templates/interface_template_search_menu.cc
index 7639643aee8..03ad498fe9b 100644
--- a/source/blender/editors/interface/templates/interface_template_search_menu.cc
+++ b/source/blender/editors/interface/templates/interface_template_search_menu.cc
@@ -624,10 +624,7 @@ static MenuSearch_Data *menu_items_from_ui_create(bContext *C,
           SPACE_MENU_MAP(SPACE_INFO, "INFO_MT_editor_menus");
           SPACE_MENU_MAP(SPACE_SEQ, "SEQUENCER_MT_editor_menus");
           SPACE_MENU_MAP(SPACE_TEXT, "TEXT_MT_editor_menus");
-          SPACE_MENU_MAP(SPACE_ACTION,
-                         (((const SpaceAction *)sl)->mode == SACTCONT_TIMELINE) ?
-                             "TIME_MT_editor_menus" :
-                             "DOPESHEET_MT_editor_menus");
+          SPACE_MENU_MAP(SPACE_ACTION, "DOPESHEET_MT_editor_menus");
           SPACE_MENU_MAP(SPACE_NLA, "NLA_MT_editor_menus");
           SPACE_MENU_MAP(SPACE_NODE, "NODE_MT_editor_menus");
           SPACE_MENU_MAP(SPACE_CONSOLE, "CONSOLE_MT_editor_menus");
diff --git a/source/blender/editors/screen/screen_ops.cc b/source/blender/editors/screen/screen_ops.cc
index 73f07eb99c3..49609e61c25 100644
--- a/source/blender/editors/screen/screen_ops.cc
+++ b/source/blender/editors/screen/screen_ops.cc
@@ -5584,12 +5584,8 @@ static bool match_region_with_redraws(const ScrArea *area,
     }
   }
   else if (regiontype == RGN_TYPE_HEADER) {
-    if (spacetype == SPACE_ACTION) {
-      /* The timeline shows the current frame in the header. Other headers
-       * don't need to be updated. */
-      SpaceAction *saction = (SpaceAction *)area->spacedata.first;
-      return saction->mode == SACTCONT_TIMELINE;
-    }
+    /* Since the timeline does not exist anymore, this doesn't need updating. */
+    return false;
   }
   else if (regiontype == RGN_TYPE_FOOTER) {
     /* The footer region in animation editors shows the current frame. */
diff --git a/source/blender/editors/space_action/action_draw.cc b/source/blender/editors/space_action/action_draw.cc
index 6810beca53a..14fbaac7d8b 100644
--- a/source/blender/editors/space_action/action_draw.cc
+++ b/source/blender/editors/space_action/action_draw.cc
@@ -319,10 +319,6 @@ static void draw_keyframes(bAnimContext *ac,
   int action_flag = saction->flag;
   bDopeSheet *ads = &saction->ads;
 
-  if (saction->mode == SACTCONT_TIMELINE) {
-    action_flag &= ~(SACTION_SHOW_INTERPOLATION | SACTION_SHOW_EXTREMES);
-  }
-
   const float channel_step = ANIM_UI_get_channel_step();
   float ymax = ANIM_UI_get_first_channel_top(v2d);
 
diff --git a/source/blender/editors/space_action/space_action.cc b/source/blender/editors/space_action/space_action.cc
index 7886aa2c3e8..05339c72b28 100644
--- a/source/blender/editors/space_action/space_action.cc
+++ b/source/blender/editors/space_action/space_action.cc
@@ -564,7 +564,7 @@ static void action_listener(const wmSpaceTypeListenerParams *params)
   switch (wmn->category) {
     case NC_GPENCIL:
       /* only handle these events for containers in which GPencil frames are displayed */
-      if (ELEM(saction->mode, SACTCONT_GPENCIL, SACTCONT_DOPESHEET, SACTCONT_TIMELINE)) {
+      if (ELEM(saction->mode, SACTCONT_GPENCIL, SACTCONT_DOPESHEET)) {
         if (wmn->action == NA_EDITED) {
           ED_area_tag_redraw(area);
         }
@@ -626,10 +626,8 @@ static void action_listener(const wmSpaceTypeListenerParams *params)
           }
           break;
         default:
-          if (saction->mode != SACTCONT_TIMELINE) {
-            /* Just redrawing the view will do. */
-            ED_area_tag_redraw(area);
-          }
+          /* Just redrawing the view will do. */
+          ED_area_tag_redraw(area);
           break;
       }
       break;
@@ -647,11 +645,6 @@ static void action_listener(const wmSpaceTypeListenerParams *params)
         case ND_POINTCACHE:
         case ND_MODIFIER:
         case ND_PARTICLE:
-          /* only needed in timeline mode */
-          if (saction->mode == SACTCONT_TIMELINE) {
-            ED_area_tag_refresh(area);
-            ED_area_tag_redraw(area);
-          }
           break;
         default: /* just redrawing the view will do */
           ED_area_tag_redraw(area);
@@ -710,39 +703,18 @@ static void action_listener(const wmSpaceTypeListenerParams *params)
 
 static void action_header_region_listener(const wmRegionListenerParams *params)
 {
-  ScrArea *area = params->area;
   ARegion *region = params->region;
   const wmNotifier *wmn = params->notifier;
-  SpaceAction *saction = (SpaceAction *)area->spacedata.first;
 
   /* context changes */
   switch (wmn->category) {
     case NC_SCREEN:
-      if (saction->mode == SACTCONT_TIMELINE) {
-        if (wmn->data == ND_ANIMPLAY) {
-          ED_region_tag_redraw(region);
-        }
-      }
       break;
     case NC_SCENE:
-      if (saction->mode == SACTCONT_TIMELINE) {
-        switch (wmn->data) {
-          case ND_RENDER_RESULT:
-          case ND_OB_SELECT:
-          case ND_FRAME:
-          case ND_FRAME_RANGE:
-          case ND_KEYINGSET:
-          case ND_RENDER_OPTIONS:
-            ED_region_tag_redraw(region);
-            break;
-        }
-      }
-      else {
-        switch (wmn->data) {
-          case ND_OB_ACTIVE:
-            ED_region_tag_redraw(region);
-            break;
-        }
+      switch (wmn->data) {
+        case ND_OB_ACTIVE:
+          ED_region_tag_redraw(region);
+          break;
       }
       break;
     case NC_ID:
@@ -898,54 +870,6 @@ static void action_foreach_id(SpaceLink *space_link, LibraryForeachIDData *data)
   }
 }
 
-/**
- * \note Used for splitting out a subset of modes is more involved,
- * The previous non-timeline mode is stored so switching back to the
- * dope-sheet doesn't always reset the sub-mode.
- */
-static int action_space_subtype_get(ScrArea *area)
-{
-  SpaceAction *sact = static_cast<SpaceAction *>(area->spacedata.first);
-  return sact->mode == SACTCONT_TIMELINE ? SACTCONT_TIMELINE : SACTCONT_DOPESHEET;
-}
-
-static void action_space_subtype_set(ScrArea *area, int value)
-{
-  SpaceAction *sact = static_cast<SpaceAction *>(area->spacedata.first);
-  if (value == SACTCONT_TIMELINE) {
-    if (sact->mode != SACTCONT_TIMELINE) {
-      sact->mode_prev = sact->mode;
-    }
-    sact->mode = value;
-  }
-  else {
-    sact->mode = sact->mode_prev;
-  }
-}
-
-static void action_space_subtype_item_extend(bContext * /*C*/,
-                                             EnumPropertyItem **item,
-                                             int *totitem)
-{
-  RNA_enum_items_add(item, totitem, rna_enum_space_action_mode_items);
-}
-
-static blender::StringRefNull action_space_name_get(const ScrArea *area)
-{
-  SpaceAction *sact = static_cast<SpaceAction *>(area->spacedata.first);
-  const int index = max_ii(0, RNA_enum_from_value(rna_enum_space_action_mode_items, sact->mode));
-  const EnumPropertyItem item = rna_enum_space_action_mode_items[index];
-  return item.name;
-}
-
-static int action_space_icon_get(const ScrArea *area)
-{
-  SpaceAction *sact = static_cast<SpaceAction *>(area->spacedata.first);
-  const int index = max_ii(0, RNA_enum_from_value(rna_enum_space_action_mode_items, sact->mode));
-  const EnumPropertyItem item = rna_enum_space_action_mode_items[index];
-  return item.icon;
-}
-
 static void action_space_blend_read_data(BlendDataReader * /*reader*/, SpaceLink *sl)
 {
   SpaceAction *saction = (SpaceAction *)sl;
@@ -975,11 +899,6 @@ void ED_spacetype_action()
   st->refresh = action_refresh;
   st->id_remap = action_id_remap;
   st->foreach_id = action_foreach_id;
-  st->space_subtype_item_extend = action_space_subtype_item_extend;
-  st->space_subtype_get = action_space_subtype_get;
-  st->space_subtype_set = action_space_subtype_set;
-  st->space_name_get = action_space_name_get;
-  st->space_icon_get = action_space_icon_get;
   st->blend_read_data = action_space_blend_read_data;
   st->blend_read_after_liblink = nullptr;
   st->blend_write = action_space_blend_write;
diff --git a/source/blender/makesrna/RNA_enum_items.hh b/source/blender/makesrna/RNA_enum_items.hh
index 5f9b424617e..b99926dd40a 100644
--- a/source/blender/makesrna/RNA_enum_items.hh
+++ b/source/blender/makesrna/RNA_enum_items.hh
@@ -38,7 +38,6 @@ DEF_ENUM(rna_enum_space_sequencer_view_type_items)
 DEF_ENUM(rna_enum_space_type_items)
 DEF_ENUM(rna_enum_space_image_mode_items)
 DEF_ENUM(rna_enum_space_image_mode_all_items)
-DEF_ENUM(rna_enum_space_action_mode_items)
 DEF_ENUM(rna_enum_fileselect_params_sort_items)
 DEF_ENUM(rna_enum_region_type_items)
 DEF_ENUM(rna_enum_object_modifier_type_items)
diff --git a/source/blender/makesrna/intern/rna_action.cc b/source/blender/makesrna/intern/rna_action.cc
index 1c3db9d3892..2b1913bd5d7 100644
--- a/source/blender/makesrna/intern/rna_action.cc
+++ b/source/blender/makesrna/intern/rna_action.cc
@@ -1507,7 +1507,6 @@ bool rna_Action_actedit_assign_poll(PointerRNA *ptr, PointerRNA value)
     case SACTCONT_DOPESHEET:
     case SACTCONT_MASK:
     case SACTCONT_CACHEFILE:
-    case SACTCONT_TIMELINE:
       break;
   }
 
diff --git a/source/blender/makesrna/intern/rna_space.cc b/source/blender/makesrna/intern/rna_space.cc
index 6c9b67c98e4..f59632b585c 100644
--- a/source/blender/makesrna/intern/rna_space.cc
+++ b/source/blender/makesrna/intern/rna_space.cc
@@ -212,10 +212,6 @@ const EnumPropertyItem rna_enum_space_file_browse_mode_items[] = {
   { \
     SACTCONT_DOPESHEET, "DOPESHEET", ICON_ACTION, "Dope Sheet", "Edit all keyframes in scene" \
   }
-#define SACT_ITEM_TIMELINE \
-  { \
-    SACTCONT_TIMELINE, "TIMELINE", ICON_TIME, "Timeline", "Timeline and playback controls" \
-  }
 #define SACT_ITEM_ACTION \
   { \
     SACTCONT_ACTION, "ACTION", ICON_OBJECT_DATA, "Action Editor", \
@@ -246,7 +242,6 @@ const EnumPropertyItem rna_enum_space_file_browse_mode_items[] = {
  * so show that using object-icon hint */
 static EnumPropertyItem rna_enum_space_action_mode_all_items[] = {
     SACT_ITEM_DOPESHEET,
-    SACT_ITEM_TIMELINE,
     SACT_ITEM_ACTION,
     SACT_ITEM_SHAPEKEY,
     SACT_ITEM_GPENCIL,
@@ -256,7 +251,6 @@ static EnumPropertyItem rna_enum_space_action_mode_all_items[] = {
 };
 static EnumPropertyItem rna_enum_space_action_ui_mode_items[] = {
     SACT_ITEM_DOPESHEET,
-    /* SACT_ITEM_TIMELINE, */
     SACT_ITEM_ACTION,
     SACT_ITEM_SHAPEKEY,
     SACT_ITEM_GPENCIL,
@@ -266,16 +260,7 @@ static EnumPropertyItem rna_enum_space_action_ui_mode_items[] = {
 };
 #endif
 
-/* Expose as `ui_mode`. */
-
-const EnumPropertyItem rna_enum_space_action_mode_items[] = {
-    SACT_ITEM_DOPESHEET,
-    SACT_ITEM_TIMELINE,
-    {0, nullptr, 0, nullptr, nullptr},
-};
-
 #undef SACT_ITEM_DOPESHEET
-#undef SACT_ITEM_TIMELINE
 #undef SACT_ITEM_ACTION
 #undef SACT_ITEM_SHAPEKEY
 #undef SACT_ITEM_GPENCIL
@@ -2349,21 +2334,10 @@ static void rna_SpaceDopeSheetEditor_mode_update(bContext *C, PointerRNA *ptr)
   SpaceAction *saction = (SpaceAction *)(ptr->data);
   ScrArea *area = CTX_wm_area(C);
 
-  /* Collapse (and show) summary channel and hide channel list for timeline */
-  if (saction->mode == SACTCONT_TIMELINE) {
-    saction->ads.flag |= ADS_FLAG_SUMMARY_COLLAPSED;
-    saction->ads.filterflag |= ADS_FILTER_SUMMARY;
-  }
-
   if (area && area->spacedata.first == saction) {
     ARegion *channels_region = BKE_area_find_region_type(area, RGN_TYPE_CHANNELS);
     if (channels_region) {
-      if (saction->mode == SACTCONT_TIMELINE) {
-        channels_region->flag |= RGN_FLAG_HIDDEN;
-      }
-      else {
-        channels_region->flag &= ~RGN_FLAG_HIDDEN;
-      }
+      channels_region->flag &= ~RGN_FLAG_HIDDEN;
       ED_region_visibility_change_update(C, area, channels_region);
     }
   }
@@ -2373,9 +2347,7 @@ static void rna_SpaceDopeSheetEditor_mode_update(bContext *C, PointerRNA *ptr)
 
   /* store current mode as "old mode",
    * so that returning from other editors doesn't always reset to "Action Editor" */
-  if (saction->mode != SACTCONT_TIMELINE) {
-    saction->mode_prev = saction->mode;
-  }
+  saction->mode_prev = saction->mode;
 }
 
 /* Space Graph Editor */