diff --git a/source/blender/animrig/intern/versioning.cc b/source/blender/animrig/intern/versioning.cc
index 92d8a93085e..c28a83f1c68 100644
--- a/source/blender/animrig/intern/versioning.cc
+++ b/source/blender/animrig/intern/versioning.cc
@@ -18,6 +18,7 @@
 #include "DNA_action_defaults.h"
 #include "DNA_action_types.h"
 
+#include "BKE_lib_id.hh"
 #include "BKE_main.hh"
 #include "BKE_node.hh"
 #include "BKE_report.hh"
@@ -138,7 +139,7 @@ void convert_legacy_animato_action(bAction &dna_action)
 
 void tag_action_user_for_slotted_actions_conversion(ID &animated_id)
 {
-  animated_id.runtime.readfile_data->tags.action_assignment_needs_slot = true;
+  animated_id.runtime->readfile_data->tags.action_assignment_needs_slot = true;
 }
 
 void tag_action_users_for_slotted_actions_conversion(Main &bmain)
diff --git a/source/blender/blenkernel/BKE_lib_id.hh b/source/blender/blenkernel/BKE_lib_id.hh
index a1242cd5554..2b2079f8ea6 100644
--- a/source/blender/blenkernel/BKE_lib_id.hh
+++ b/source/blender/blenkernel/BKE_lib_id.hh
@@ -42,8 +42,10 @@
 #include "DNA_userdef_enums.h"
 
 struct BlendWriter;
+struct Depsgraph;
 struct GHash;
 struct ID;
+struct ID_Readfile_Data;
 struct Library;
 struct ListBase;
 struct Main;
@@ -51,6 +53,41 @@ struct PointerRNA;
 struct PropertyRNA;
 struct bContext;
 
+namespace blender::bke::id {
+
+/** Status used and counters created during id-remapping. */
+struct ID_Runtime_Remap {
+  /** Status during ID remapping. */
+  int status = 0;
+  /** During ID remapping the number of skipped use cases that refcount the data-block. */
+  int skipped_refcounted = 0;
+  /**
+   * During ID remapping the number of direct use cases that could be remapped
+   * (e.g. obdata when in edit mode).
+   */
+  int skipped_direct = 0;
+  /** During ID remapping, the number of indirect use cases that could not be remapped. */
+  int skipped_indirect = 0;
+};
+
+struct ID_Runtime {
+  ID_Runtime_Remap remap = {};
+  /**
+   * The depsgraph that owns this data block. This is only set on data-blocks which are
+   * copied-on-eval by the depsgraph. Additional data-blocks created during depsgraph evaluation
+   * are not owned by any specific depsgraph and thus this pointer is null for those.
+   */
+  Depsgraph *depsgraph = nullptr;
+
+  /**
+   * This data is only allocated & used during the readfile process. After that, the memory is
+   * freed and the pointer set to `nullptr`.
+   */
+  ID_Readfile_Data *readfile_data = nullptr;
+};
+
+}  // namespace blender::bke::id
+
 /**
  * Get allocation size of a given data-block type and optionally allocation `r_name`.
  */
@@ -58,6 +95,9 @@ size_t BKE_libblock_get_alloc_info(short type, const char **r_name);
 /**
  * Allocates and returns memory of the right size for the specified block type,
  * initialized to zero.
+ *
+ * \note: Typically, caller also needs to immediately call #BKE_libblock_runtime_ensure on the
+ * allocated ID data.
  */
 ID *BKE_libblock_alloc_notest(short type) ATTR_WARN_UNUSED_RESULT;
 /**
@@ -90,6 +130,14 @@ void *BKE_libblock_alloc_in_lib(Main *bmain,
  */
 void BKE_libblock_init_empty(ID *id) ATTR_NONNULL(1);
 
+/**
+ * Ensure that the given ID does have a valid runtime data.
+ *
+ * Low-level API, should not be needed in typical ID usages, where ID::runtime can always be
+ * assumed valid.
+ */
+void BKE_libblock_runtime_ensure(ID &id);
+
 /**
  * Reset the runtime counters used by ID remapping.
  */
@@ -445,20 +493,35 @@ enum {
 /**
  * Low-level ID freeing functions.
  *
- * \note These functions do NOT cover embedded IDs. Those are managed by the
+ * \note These `BKE_libblock_free_` functions do NOT cover embedded IDs. Those are managed by the
  * owning ID, and are typically allocated/freed from the IDType callbacks.
  */
-void BKE_libblock_free_datablock(ID *id, int flag) ATTR_NONNULL();
-void BKE_libblock_free_data(ID *id, bool do_id_user) ATTR_NONNULL();
-void BKE_libblock_free_runtime_data(ID *id) ATTR_NONNULL();
 
 /**
+ * Only free generic Python instance data (ID::py_instance).
+ *
  * In most cases #BKE_id_free_ex handles this, when lower level functions are called directly
  * this function will need to be called too, if Python has access to the data.
  *
  * ID data-blocks such as #Material.nodetree are not stored in #Main.
  */
 void BKE_libblock_free_data_py(ID *id);
+/**
+ * Only free generic runtime data (ID::runtime).
+ *
+ * In most cases #BKE_libblock_free_data handles this, but in rare cases (currently in readfile,
+ * when freeing linked ID placeholders), it is necessary.
+ */
+void BKE_libblock_free_runtime_data(ID *id);
+
+/** Free generic ID data, including the runtime and animation data, but not the python data. */
+void BKE_libblock_free_data(ID *id, bool do_id_user) ATTR_NONNULL();
+
+/**
+ * Free IDtype-specific data (does _not_ free generic ID data, use
+ * #BKE_libblock_free_data for that).
+ */
+void BKE_libblock_free_datablock(ID *id, int flag) ATTR_NONNULL();
 
 /**
  * Complete ID freeing, extended version for corner cases.
diff --git a/source/blender/blenkernel/intern/lib_id.cc b/source/blender/blenkernel/intern/lib_id.cc
index 82f1a2afa96..fc3bc9c10b2 100644
--- a/source/blender/blenkernel/intern/lib_id.cc
+++ b/source/blender/blenkernel/intern/lib_id.cc
@@ -1300,6 +1300,13 @@ void BKE_main_lib_objects_recalc_all(Main *bmain)
  *
  * **************************** */
 
+void BKE_libblock_runtime_ensure(ID &id)
+{
+  if (!id.runtime) {
+    id.runtime = MEM_new<blender::bke::id::ID_Runtime>(__func__);
+  }
+}
+
 size_t BKE_libblock_get_alloc_info(short type, const char **r_name)
 {
   const IDTypeInfo *id_type = BKE_idtype_get_info_from_idcode(type);
@@ -1322,7 +1329,8 @@ ID *BKE_libblock_alloc_notest(short type)
   const char *name;
   size_t size = BKE_libblock_get_alloc_info(type, &name);
   if (size != 0) {
-    return static_cast<ID *>(MEM_callocN(size, name));
+    ID *id = static_cast<ID *>(MEM_callocN(size, name));
+    return id;
   }
   BLI_assert_msg(0, "Request to allocate unknown data type");
   return nullptr;
@@ -1339,6 +1347,7 @@ void *BKE_libblock_alloc_in_lib(Main *bmain,
   BLI_assert((flag & LIB_ID_CREATE_NO_MAIN) != 0 || (flag & LIB_ID_CREATE_LOCAL) == 0);
 
   ID *id = BKE_libblock_alloc_notest(type);
+  BKE_libblock_runtime_ensure(*id);
 
   if (id) {
     if ((flag & LIB_ID_CREATE_NO_MAIN) != 0) {
@@ -1443,10 +1452,10 @@ void BKE_libblock_init_empty(ID *id)
 
 void BKE_libblock_runtime_reset_remapping_status(ID *id)
 {
-  id->runtime.remap.status = 0;
-  id->runtime.remap.skipped_refcounted = 0;
-  id->runtime.remap.skipped_direct = 0;
-  id->runtime.remap.skipped_indirect = 0;
+  id->runtime->remap.status = 0;
+  id->runtime->remap.skipped_refcounted = 0;
+  id->runtime->remap.skipped_direct = 0;
+  id->runtime->remap.skipped_indirect = 0;
 }
 
 /* ********** ID session-wise UID management. ********** */
@@ -1550,6 +1559,7 @@ void BKE_libblock_copy_in_lib(Main *bmain,
      * Clear and initialize it similar to BKE_libblock_alloc_in_lib. */
     const size_t size = BKE_libblock_get_alloc_info(GS(id->name), nullptr);
     memset(new_id, 0, size);
+    BKE_libblock_runtime_ensure(*new_id);
     STRNCPY(new_id->name, id->name);
     new_id->us = 0;
     new_id->tag |= ID_TAG_NOT_ALLOCATED | ID_TAG_NO_MAIN | ID_TAG_NO_USER_REFCOUNT;
diff --git a/source/blender/blenkernel/intern/lib_id_delete.cc b/source/blender/blenkernel/intern/lib_id_delete.cc
index e3775dc1bc3..72e3828ba48 100644
--- a/source/blender/blenkernel/intern/lib_id_delete.cc
+++ b/source/blender/blenkernel/intern/lib_id_delete.cc
@@ -71,9 +71,9 @@ void BKE_libblock_free_data(ID *id, const bool do_id_user)
     MEM_freeN(id->library_weak_reference);
   }
 
-  BKE_libblock_free_runtime_data(id);
-
   BKE_animdata_free(id, do_id_user);
+
+  BKE_libblock_free_runtime_data(id);
 }
 
 void BKE_libblock_free_datablock(ID *id, const int /*flag*/)
@@ -92,11 +92,15 @@ void BKE_libblock_free_datablock(ID *id, const int /*flag*/)
 
 void BKE_libblock_free_runtime_data(ID *id)
 {
-  /* During "normal" file loading this data is released when versioning ends. Some versioning code
-   * also deletes IDs, though. For example, in the startup blend file, brushes that were replaced
-   * by assets are deleted. This means that the regular "delete this ID" flow (aka this code here)
-   * also needs to free this data. */
-  BLO_readfile_id_runtime_data_free(*id);
+  if (id->runtime) {
+    /* During "normal" file loading this data is released when versioning ends. Some versioning
+     * code also deletes IDs, though. For example, in the startup blend file, brushes that were
+     * replaced by assets are deleted. This means that the regular "delete this ID" flow (aka this
+     * code here) also needs to free this data. */
+    BLO_readfile_id_runtime_data_free(*id);
+
+    MEM_SAFE_DELETE(id->runtime);
+  }
 }
 
 static int id_free(Main *bmain, void *idv, int flag, const bool use_flag_from_idtag)
diff --git a/source/blender/blenkernel/intern/lib_remap.cc b/source/blender/blenkernel/intern/lib_remap.cc
index 873536f0b98..d0f9f43736a 100644
--- a/source/blender/blenkernel/intern/lib_remap.cc
+++ b/source/blender/blenkernel/intern/lib_remap.cc
@@ -82,21 +82,21 @@ static void foreach_libblock_remap_callback_skip(const ID * /*id_owner*/,
   BLI_assert(id != nullptr);
 
   if (is_indirect) {
-    id->runtime.remap.skipped_indirect++;
+    id->runtime->remap.skipped_indirect++;
   }
   else if (violates_never_null || is_obj_editmode || is_reference) {
-    id->runtime.remap.skipped_direct++;
+    id->runtime->remap.skipped_direct++;
   }
   else {
     BLI_assert_unreachable();
   }
 
   if (cb_flag & IDWALK_CB_USER) {
-    id->runtime.remap.skipped_refcounted++;
+    id->runtime->remap.skipped_refcounted++;
   }
   else if (cb_flag & IDWALK_CB_USER_ONE) {
     /* No need to count number of times this happens, just a flag is enough. */
-    id->runtime.remap.status |= ID_REMAP_IS_USER_ONE_SKIPPED;
+    id->runtime->remap.status |= ID_REMAP_IS_USER_ONE_SKIPPED;
   }
 }
 
@@ -141,7 +141,7 @@ static void foreach_libblock_remap_callback_apply(ID *id_owner,
   ID *new_id = violates_never_null ? nullptr : *id_ptr;
 
   if (!is_indirect && new_id) {
-    new_id->runtime.remap.status |= ID_REMAP_IS_LINKED_DIRECT;
+    new_id->runtime->remap.status |= ID_REMAP_IS_LINKED_DIRECT;
   }
 
   if (skip_user_refcount) {
@@ -444,7 +444,7 @@ static void libblock_remap_data_update_tags(ID *old_id, ID *new_id, IDRemap *id_
   }
 
   if (new_id != nullptr && (new_id->tag & ID_TAG_INDIRECT) &&
-      (new_id->runtime.remap.status & ID_REMAP_IS_LINKED_DIRECT))
+      (new_id->runtime->remap.status & ID_REMAP_IS_LINKED_DIRECT))
   {
     new_id->tag &= ~ID_TAG_INDIRECT;
     new_id->flag &= ~ID_FLAG_INDIRECT_WEAK_LINK;
@@ -569,13 +569,13 @@ static void libblock_remap_foreach_idpair(ID *old_id, ID *new_id, Main *bmain, i
      * count has actually been incremented for that, we have to decrease once more its user
      * count... unless we had to skip some 'user_one' cases. */
     if ((old_id->tag & ID_TAG_EXTRAUSER_SET) &&
-        !(old_id->runtime.remap.status & ID_REMAP_IS_USER_ONE_SKIPPED))
+        !(old_id->runtime->remap.status & ID_REMAP_IS_USER_ONE_SKIPPED))
     {
       id_us_clear_real(old_id);
     }
   }
 
-  const int skipped_refcounted = old_id->runtime.remap.skipped_refcounted;
+  const int skipped_refcounted = old_id->runtime->remap.skipped_refcounted;
   if (old_id->us - skipped_refcounted < 0) {
     CLOG_ERROR(&LOG,
                "Error in remapping process from '%s' (%p) to '%s' (%p): "
@@ -587,7 +587,7 @@ static void libblock_remap_foreach_idpair(ID *old_id, ID *new_id, Main *bmain, i
                old_id->us - skipped_refcounted);
   }
 
-  const int skipped_direct = old_id->runtime.remap.skipped_direct;
+  const int skipped_direct = old_id->runtime->remap.skipped_direct;
   if (skipped_direct == 0) {
     /* old_id is assumed to not be used directly anymore... */
     if (old_id->lib && (old_id->tag & ID_TAG_EXTERN)) {
diff --git a/source/blender/blenloader/intern/readfile.cc b/source/blender/blenloader/intern/readfile.cc
index 375b03fe105..e130c354ac6 100644
--- a/source/blender/blenloader/intern/readfile.cc
+++ b/source/blender/blenloader/intern/readfile.cc
@@ -2191,29 +2191,29 @@ static int direct_link_id_restore_recalc(const FileData *fd,
 
 static void readfile_id_runtime_data_ensure(ID &id)
 {
-  if (id.runtime.readfile_data) {
+  if (id.runtime->readfile_data) {
     return;
   }
-  id.runtime.readfile_data = MEM_callocN<ID_Readfile_Data>(__func__);
+  id.runtime->readfile_data = MEM_callocN<ID_Readfile_Data>(__func__);
 }
 
 ID_Readfile_Data::Tags BLO_readfile_id_runtime_tags(ID &id)
 {
-  if (!id.runtime.readfile_data) {
+  if (!id.runtime->readfile_data) {
     return ID_Readfile_Data::Tags{};
   }
-  return id.runtime.readfile_data->tags;
+  return id.runtime->readfile_data->tags;
 }
 
 ID_Readfile_Data::Tags &BLO_readfile_id_runtime_tags_for_write(ID &id)
 {
   readfile_id_runtime_data_ensure(id);
-  return id.runtime.readfile_data->tags;
+  return id.runtime->readfile_data->tags;
 }
 
 void BLO_readfile_id_runtime_data_free(ID &id)
 {
-  MEM_SAFE_FREE(id.runtime.readfile_data);
+  MEM_SAFE_FREE(id.runtime->readfile_data);
 }
 
 void BLO_readfile_id_runtime_data_free_all(Main &bmain)
@@ -2246,6 +2246,9 @@ static void direct_link_id_common(BlendDataReader *reader,
                                   const int id_tag,
                                   const ID_Readfile_Data::Tags id_read_tags)
 {
+  BLI_assert(id->runtime == nullptr);
+  BKE_libblock_runtime_ensure(*id);
+
   if (!BLO_read_data_is_undo(reader)) {
     /* When actually reading a file, we do want to reset/re-generate session UIDS.
      * In undo case, we want to re-use existing ones. */
@@ -2271,13 +2274,8 @@ static void direct_link_id_common(BlendDataReader *reader,
     id->tag = id_tag;
   }
 
-  if (!BLO_read_data_is_undo(reader)) {
-    /* Reset the runtime data, as there were versions of Blender that did not do
-     * this before writing to disk. */
-    id->runtime = ID_Runtime{};
-  }
   readfile_id_runtime_data_ensure(*id);
-  id->runtime.readfile_data->tags = id_read_tags;
+  id->runtime->readfile_data->tags = id_read_tags;
 
   if ((id_tag & ID_TAG_TEMP_MAIN) == 0) {
     BKE_lib_libblock_session_uid_ensure(id);
@@ -2561,6 +2559,7 @@ static ID *create_placeholder(Main *mainvar,
 {
   ListBase *lb = which_libbase(mainvar, idcode);
   ID *ph_id = BKE_libblock_alloc_notest(idcode);
+  BKE_libblock_runtime_ensure(*ph_id);
 
   *((short *)ph_id->name) = idcode;
   BLI_strncpy(ph_id->name + 2, idname, sizeof(ph_id->name) - 2);
@@ -4953,15 +4952,19 @@ static void read_library_linked_ids(FileData *basefd, FileData *fd, Main *mainva
         /* Transfer the readfile data from the placeholder to the real ID, but
          * only if the real ID has no readfile data yet. The same realid may be
          * referred to by multiple placeholders. */
-        if (realid && !realid->runtime.readfile_data) {
-          realid->runtime.readfile_data = id->runtime.readfile_data;
-          id->runtime.readfile_data = nullptr;
+        if (realid && !realid->runtime->readfile_data) {
+          realid->runtime->readfile_data = id->runtime->readfile_data;
+          id->runtime->readfile_data = nullptr;
         }
 
-        /* The 'readfile' runtime data needs to be freed here, as this ID placeholder does not go
-         * through versioning (the usual place where this data is freed). Since `id` is not a real
-         * ID, this shouldn't follow any pointers to embedded IDs. */
-        BLO_readfile_id_runtime_data_free(*id);
+        /* Ensure that the runtime pointer, and its 'readfile' sub-data, are properly freed, as
+         * this ID placeholder does not go through versioning (the usual place where this data is
+         * freed). Since `id` is not a real ID, this shouldn't follow any pointers to embedded IDs.
+         *
+         * WARNING! This placeholder ID is only an ID struct, with a very small subset of regular
+         * ID common data actually valid and needing to be freed. Therefore, calling
+         * #BKE_libblock_free_data on it would not work. */
+        BKE_libblock_free_runtime_data(id);
 
         MEM_freeN(id);
       }
diff --git a/source/blender/blenloader/intern/writefile.cc b/source/blender/blenloader/intern/writefile.cc
index a035ce11025..e7c7c8281e2 100644
--- a/source/blender/blenloader/intern/writefile.cc
+++ b/source/blender/blenloader/intern/writefile.cc
@@ -1336,6 +1336,7 @@ BLO_Write_IDBuffer::BLO_Write_IDBuffer(ID &id, const bool is_undo, const bool is
   }
   temp_id->us = 0;
   temp_id->icon_id = 0;
+  temp_id->runtime = nullptr;
   /* Those listbase data change every time we add/remove an ID, and also often when
    * renaming one (due to re-sorting). This avoids generating a lot of false 'is changed'
    * detections between undo steps. */
@@ -1349,8 +1350,6 @@ BLO_Write_IDBuffer::BLO_Write_IDBuffer(ID &id, const bool is_undo, const bool is
    * when we need to re-read the ID into its original address, this is currently cleared in
    * #direct_link_id_common in `readfile.cc` anyway. */
   temp_id->py_instance = nullptr;
-  /* Clear runtime data struct. */
-  temp_id->runtime = ID_Runtime{};
 }
 
 BLO_Write_IDBuffer::BLO_Write_IDBuffer(ID &id, BlendWriter *writer)
diff --git a/source/blender/depsgraph/intern/depsgraph_query.cc b/source/blender/depsgraph/intern/depsgraph_query.cc
index 68eb54db081..93add3829a4 100644
--- a/source/blender/depsgraph/intern/depsgraph_query.cc
+++ b/source/blender/depsgraph/intern/depsgraph_query.cc
@@ -14,6 +14,7 @@
 
 #include "BKE_action.hh" /* XXX: BKE_pose_channel_find_name */
 #include "BKE_idtype.hh"
+#include "BKE_lib_id.hh"
 #include "BKE_main.hh"
 
 #include "DNA_object_types.h"
@@ -283,7 +284,7 @@ const ID *DEG_get_original_id(const ID *id)
 
 Depsgraph *DEG_get_depsgraph_by_id(const ID &id)
 {
-  return id.runtime.depsgraph;
+  return id.runtime->depsgraph;
 }
 
 bool DEG_is_original_id(const ID *id)
diff --git a/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc b/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc
index de2530609cb..25b828d0e63 100644
--- a/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc
+++ b/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc
@@ -753,9 +753,15 @@ ID *deg_expand_eval_copy_datablock(const Depsgraph *depsgraph, const IDNode *id_
   DEG_COW_PRINT(
       "Expanding datablock for %s: id_orig=%p id_cow=%p\n", id_orig->name, id_orig, id_cow);
 
-  /* Sanity checks. */
+  /* Sanity checks.
+   *
+   * At this point, `id_cow` is essentially considered as a (partially dirty) allocated buffer (it
+   * has been freed, but not fully cleared, as a result of calling #deg_free_eval_copy_datablock on
+   * it). It is not expected to have any valid sub-data, not even a valid `ID::runtime` pointer.
+   */
   BLI_assert(check_datablock_expanded(id_cow) == false);
   BLI_assert(id_cow->py_instance == nullptr);
+  BLI_assert(id_cow->runtime == nullptr);
 
   /* Copy data from original ID to a copied version. */
   /* TODO(sergey): Avoid doing full ID copy somehow, make Mesh to reference
@@ -1022,7 +1028,7 @@ void deg_tag_eval_copy_id(deg::Depsgraph &depsgraph, ID *id_cow, const ID *id_or
   /* This ID is no longer localized, is a self-sustaining copy now. */
   id_cow->tag &= ~ID_TAG_LOCALIZED;
   id_cow->orig_id = (ID *)id_orig;
-  id_cow->runtime.depsgraph = &reinterpret_cast<::Depsgraph &>(depsgraph);
+  id_cow->runtime->depsgraph = &reinterpret_cast<::Depsgraph &>(depsgraph);
 }
 
 bool deg_eval_copy_is_expanded(const ID *id_cow)
diff --git a/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.h b/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.h
index 7da923ae296..f4cbc14059c 100644
--- a/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.h
+++ b/source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.h
@@ -13,6 +13,7 @@
 #include "DNA_ID.h"
 
 struct ID;
+struct Depsgraph;
 
 /* Uncomment this to have verbose log about original and evaluated pointers
  * logged, with detailed information when they are allocated, expanded
diff --git a/source/blender/depsgraph/intern/node/deg_node_id.cc b/source/blender/depsgraph/intern/node/deg_node_id.cc
index ddcb7c883d7..aad8aad42f3 100644
--- a/source/blender/depsgraph/intern/node/deg_node_id.cc
+++ b/source/blender/depsgraph/intern/node/deg_node_id.cc
@@ -81,6 +81,8 @@ void IDNode::init_copy_on_write(ID *id_cow_hint)
   }
   else if (deg_eval_copy_is_needed(id_orig)) {
     id_cow = BKE_libblock_alloc_notest(GS(id_orig->name));
+    /* No need to call #BKE_libblock_runtime_ensure here, this will be done by
+     * #BKE_libblock_copy_in_lib when #deg_expand_eval_copy_datablock is executed. */
     DEG_COW_PRINT(
         "Allocate memory for %s: id_orig=%p id_cow=%p\n", id_orig->name, id_orig, id_cow);
   }
diff --git a/source/blender/editors/include/UI_interface_c.hh b/source/blender/editors/include/UI_interface_c.hh
index 446b9f66557..4d2363d0860 100644
--- a/source/blender/editors/include/UI_interface_c.hh
+++ b/source/blender/editors/include/UI_interface_c.hh
@@ -31,6 +31,7 @@
 
 struct ARegion;
 struct AutoComplete;
+struct Depsgraph;
 struct EnumPropertyItem;
 struct FileSelectParams;
 struct ID;
diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index 092b12a0b3e..55e96221bfe 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -20,6 +20,9 @@
 #ifdef __cplusplus
 #  include <type_traits>
 
+namespace blender::bke::id {
+struct ID_Runtime;
+}
 namespace blender::bke {
 struct PreviewImageRuntime;
 }
@@ -29,6 +32,7 @@ struct IDPropertyGroupChildrenSet;
 namespace blender::bke::library {
 struct LibraryRuntime;
 }
+using ID_RuntimeHandle = blender::bke::id::ID_Runtime;
 using PreviewImageRuntimeHandle = blender::bke::PreviewImageRuntime;
 using LibraryRuntimeHandle = blender::bke::library::LibraryRuntime;
 using IDPropertyGroupChildrenSet = blender::bke::idprop::IDPropertyGroupChildrenSet;
@@ -36,6 +40,7 @@ using IDPropertyGroupChildrenSet = blender::bke::idprop::IDPropertyGroupChildren
 typedef struct PreviewImageRuntimeHandle PreviewImageRuntimeHandle;
 typedef struct LibraryRuntimeHandle LibraryRuntimeHandle;
 typedef struct IDPropertyGroupChildrenSet IDPropertyGroupChildrenSet;
+typedef struct ID_RuntimeHandle ID_RuntimeHandle;
 #endif
 
 #ifdef __cplusplus
@@ -45,11 +50,9 @@ extern "C" {
 struct FileData;
 struct GHash;
 struct ID;
-struct ID_Readfile_Data;
 struct Library;
 struct PackedFile;
 struct UniqueName_Map;
-struct Depsgraph;
 
 typedef struct IDPropertyUIData {
   /** Tool-tip / property description pointer. Owned by the #IDProperty. */
@@ -380,37 +383,6 @@ enum {
   ID_REMAP_IS_USER_ONE_SKIPPED = 1 << 1,
 };
 
-/** Status used and counters created during id-remapping. */
-typedef struct ID_Runtime_Remap {
-  /** Status during ID remapping. */
-  int status;
-  /** During ID remapping the number of skipped use cases that refcount the data-block. */
-  int skipped_refcounted;
-  /**
-   * During ID remapping the number of direct use cases that could be remapped
-   * (e.g. obdata when in edit mode).
-   */
-  int skipped_direct;
-  /** During ID remapping, the number of indirect use cases that could not be remapped. */
-  int skipped_indirect;
-} ID_Runtime_Remap;
-
-typedef struct ID_Runtime {
-  ID_Runtime_Remap remap;
-  /**
-   * The depsgraph that owns this data block. This is only set on data-blocks which are
-   * copied-on-eval by the depsgraph. Additional data-blocks created during depsgraph evaluation
-   * are not owned by any specific depsgraph and thus this pointer is null for those.
-   */
-  struct Depsgraph *depsgraph;
-
-  /**
-   * This data is only allocated & used during the readfile process. After that, the memory is
-   * freed and the pointer set to `nullptr`.
-   */
-  struct ID_Readfile_Data *readfile_data;
-} ID_Runtime;
-
 typedef struct ID {
   /* There's a nasty circular dependency here.... 'void *' to the rescue! I
    * really wonder why this is needed. */
@@ -513,7 +485,17 @@ typedef struct ID {
    */
   struct LibraryWeakReference *library_weak_reference;
 
-  struct ID_Runtime runtime;
+  /**
+   * Allocated runtime data, never written on disk or in undo steps.
+   *
+   * _Always_ valid for code handling IDs managed by the `BKE_lib_id` API.
+   *
+   * Internal low-level implementation of ID creation/copying/deletion, and code handling IDs
+   * themselves in non-standard ways (mainly the CoW IDs in depsgraph, and some temporary IDs in
+   * readfile) may have to manage this pointer themselves (see also #BKE_libblock_runtime_ensure
+   * and #BKE_libblock_free_runtime_data).
+   */
+  ID_RuntimeHandle *runtime;
 } ID;
 
 /**
diff --git a/source/blender/makesdna/DNA_mask_types.h b/source/blender/makesdna/DNA_mask_types.h
index 4949bfdc5fa..39b0127f287 100644
--- a/source/blender/makesdna/DNA_mask_types.h
+++ b/source/blender/makesdna/DNA_mask_types.h
@@ -43,8 +43,6 @@ typedef struct Mask {
   int flag;
   char _pad[4];
 
-  void *_pad1;
-
   Mask_Runtime runtime;
 } Mask;
 
diff --git a/source/blender/makesdna/DNA_movieclip_types.h b/source/blender/makesdna/DNA_movieclip_types.h
index b98594227cf..171d51c98a3 100644
--- a/source/blender/makesdna/DNA_movieclip_types.h
+++ b/source/blender/makesdna/DNA_movieclip_types.h
@@ -90,8 +90,6 @@ typedef struct MovieClip {
   /** Grease pencil data. */
   struct bGPdata *gpd;
 
-  void *_pad1;
-
   /** Data for SfM tracking. */
   struct MovieTracking tracking;
   /**
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index 189021e8455..2ded1c0a399 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -2113,7 +2113,6 @@ typedef struct Scene {
   ListBase base DNA_DEPRECATED;
   /** Active base. */
   struct Base *basact DNA_DEPRECATED;
-  void *_pad1;
 
   /** 3d cursor location. */
   View3DCursor cursor;
@@ -2138,7 +2137,6 @@ typedef struct Scene {
 
   /** Default allocated now. */
   struct ToolSettings *toolsettings;
-  void *_pad4;
   struct DisplaySafeAreas safe_areas;
 
   /* Migrate or replace? depends on some internal things... */
@@ -2186,7 +2184,6 @@ typedef struct Scene {
   /** Physics simulation settings. */
   struct PhysicsSettings physics_settings;
 
-  void *_pad8;
   /**
    * XXX: runtime flag for drawing, actually belongs in the window,
    * only used by #BKE_object_handle_update()
diff --git a/source/blender/makesdna/DNA_sound_types.h b/source/blender/makesdna/DNA_sound_types.h
index 091808f010b..9ef7af6416c 100644
--- a/source/blender/makesdna/DNA_sound_types.h
+++ b/source/blender/makesdna/DNA_sound_types.h
@@ -20,6 +20,8 @@ typedef struct bSound {
 
   ID id;
 
+  void *_pad1;
+
   /**
    * The path to the sound file.
    */
diff --git a/source/blender/makesdna/DNA_text_types.h b/source/blender/makesdna/DNA_text_types.h
index 4f4a0ca15d8..a44deef7084 100644
--- a/source/blender/makesdna/DNA_text_types.h
+++ b/source/blender/makesdna/DNA_text_types.h
@@ -31,6 +31,8 @@ typedef struct Text {
 
   ID id;
 
+  void *_pad1;
+
   /**
    * Optional file path, when NULL text is considered internal.
    * Otherwise this path will be used when saving/reloading.
diff --git a/source/blender/makesdna/DNA_texture_types.h b/source/blender/makesdna/DNA_texture_types.h
index 143e1372a7c..69ed0e0874e 100644
--- a/source/blender/makesdna/DNA_texture_types.h
+++ b/source/blender/makesdna/DNA_texture_types.h
@@ -81,10 +81,11 @@ typedef struct Tex {
   /** Animation data (must be immediately after id for utilities to use it). */
   struct AnimData *adt;
 
+  void *_pad3;
+
   float noisesize, turbul;
   float bright, contrast, saturation, rfac, gfac, bfac;
   float filtersize;
-  char _pad2[4];
 
   /* newnoise: musgrave parameters */
   float mg_H, mg_lacunarity, mg_octaves, mg_offset, mg_gain;
@@ -122,7 +123,6 @@ typedef struct Tex {
   int sfra DNA_DEPRECATED;
 
   float checkerdist, nabla;
-  char _pad1[4];
 
   struct ImageUser iuser;
 
diff --git a/source/blender/makesdna/DNA_world_types.h b/source/blender/makesdna/DNA_world_types.h
index f47cd40eb36..815a777ce0a 100644
--- a/source/blender/makesdna/DNA_world_types.h
+++ b/source/blender/makesdna/DNA_world_types.h
@@ -49,17 +49,15 @@ typedef struct World {
    * bit 0: Do mist
    */
   short mode;
-  char _pad2[6];
+
+  /** Assorted settings. */
+  short flag;
 
   float misi, miststa, mistdist, misthi;
 
   /** Ambient occlusion. */
   float aodist, aoenergy;
 
-  /** Assorted settings. */
-  short flag;
-  char _pad3[2];
-
   /** Eevee settings. */
   /**
    * Resolution of the world probe when baked to a texture. Contains `eLightProbeResolution`.
@@ -73,11 +71,9 @@ typedef struct World {
   float sun_shadow_maximum_resolution;
   float sun_shadow_jitter_overblur;
   float sun_shadow_filter_radius;
-  char _pad4[4];
 
   short pr_texture;
   short use_nodes DNA_DEPRECATED;
-  char _pad[4];
 
   /* previews */
   struct PreviewImage *preview;
@@ -88,6 +84,8 @@ typedef struct World {
   /** Light-group membership information. */
   struct LightgroupMembership *lightgroup;
 
+  void *_pad1;
+
   /** Runtime. */
   ListBase gpumaterial;
   /* The Depsgraph::update_count when this World was last updated. */