diff --git a/src/khepri_machine.erl b/src/khepri_machine.erl
index 7b196535..116ae7dd 100644
--- a/src/khepri_machine.erl
+++ b/src/khepri_machine.erl
@@ -51,6 +51,9 @@
 %% </li>
 %% <li>Moved the expiration of dedups to the `tick' aux effect (see {@link
 %% handle_aux/5}). This also introduces a new command `#drop_dedups{}'.</li>
+%% <li>Added the `delete_reason' to the list of properties that can be
+%% retured. It is returned by default if the effective machine version is 2 or
+%% more.</li>
 %% </ul>
 %% </td>
 %% </tr>
@@ -98,8 +101,8 @@
 %% For internal use only.
 -export([clear_cache/1,
          ack_triggers_execution/2,
-         split_query_options/1,
-         split_command_options/1,
+         split_query_options/2,
+         split_command_options/2,
          split_put_options/1,
          insert_or_update_node/6,
          delete_matching_nodes/4,
@@ -118,7 +121,8 @@
          get_projections/1,
          has_projection/2,
          get_metrics/1,
-         get_dedups/1]).
+         get_dedups/1,
+         get_store_id/1]).
 
 -ifdef(TEST).
 -export([do_process_sync_command/3,
@@ -283,7 +287,7 @@ fold(StoreId, PathPattern, Fun, Acc, Options)
        is_function(Fun, 3) ->
     PathPattern1 = khepri_path:from_string(PathPattern),
     khepri_path:ensure_is_valid(PathPattern1),
-    {QueryOptions, TreeOptions} = split_query_options(Options),
+    {QueryOptions, TreeOptions} = split_query_options(StoreId, Options),
     Query = fun(State) ->
                     Tree = get_tree(State),
                     try
@@ -348,7 +352,8 @@ put(StoreId, PathPattern, Payload, Options)
     PathPattern1 = khepri_path:from_string(PathPattern),
     khepri_path:ensure_is_valid(PathPattern1),
     Payload1 = khepri_payload:prepare(Payload),
-    {CommandOptions, TreeAndPutOptions} = split_command_options(Options),
+    {CommandOptions, TreeAndPutOptions} = split_command_options(
+                                            StoreId, Options),
     Command = #put{path = PathPattern1,
                    payload = Payload1,
                    options = TreeAndPutOptions},
@@ -376,7 +381,7 @@ put(_StoreId, PathPattern, Payload, _Options) ->
 delete(StoreId, PathPattern, Options) when ?IS_KHEPRI_STORE_ID(StoreId) ->
     PathPattern1 = khepri_path:from_string(PathPattern),
     khepri_path:ensure_is_valid(PathPattern1),
-    {CommandOptions, TreeOptions} = split_command_options(Options),
+    {CommandOptions, TreeOptions} = split_command_options(StoreId, Options),
     %% TODO: Ensure `PutOptions' are not set this map.
     Command = #delete{path = PathPattern1,
                       options = TreeOptions},
@@ -722,14 +727,16 @@ get_projections_state(StoreId, Options)
             end,
     process_query(StoreId, Query, Options).
 
--spec split_query_options(Options) -> {QueryOptions, TreeOptions} when
+-spec split_query_options(StoreId, Options) ->
+    {QueryOptions, TreeOptions} when
+      StoreId :: khepri:store_id(),
       Options :: QueryOptions | TreeOptions,
       QueryOptions :: khepri:query_options(),
       TreeOptions :: khepri:tree_options().
 %% @private
 
-split_query_options(Options) ->
-    Options1 = set_default_options(Options),
+split_query_options(StoreId, Options) ->
+    Options1 = set_default_options(StoreId, Options),
     maps:fold(
       fun
           (Option, Value, {Q, T}) when
@@ -748,15 +755,16 @@ split_query_options(Options) ->
               {Q, T1}
       end, {#{}, #{}}, Options1).
 
--spec split_command_options(Options) ->
+-spec split_command_options(StoreId, Options) ->
     {CommandOptions, TreeAndPutOptions} when
+      StoreId :: khepri:store_id(),
       Options :: CommandOptions | TreeAndPutOptions,
       CommandOptions :: khepri:command_options(),
       TreeAndPutOptions :: khepri:tree_options() | khepri:put_options().
 %% @private
 
-split_command_options(Options) ->
-    Options1 = set_default_options(Options),
+split_command_options(StoreId, Options) ->
+    Options1 = set_default_options(StoreId, Options),
     maps:fold(
       fun
           (Option, Value, {C, TP}) when
@@ -799,7 +807,7 @@ split_put_options(TreeAndPutOptions) ->
               {T1, P}
       end, {#{}, #{}}, TreeAndPutOptions).
 
-set_default_options(Options) ->
+set_default_options(StoreId, Options) ->
     %% By default, return payload-related properties. The caller can set
     %% `props_to_return' to an empty map to get a minimal return value.
     Options1 = case Options of
@@ -808,7 +816,21 @@ set_default_options(Options) ->
                    _ ->
                        Options#{props_to_return => ?DEFAULT_PROPS_TO_RETURN}
                end,
-    Options1.
+    %% We need to remove `delete_reason' from the list if the whole cluster is
+    %% still using a machine version that doesn't know about it. Otherwise old
+    %% versions of Khepri will crash when gathering the properties.
+    PropsToReturn0 = maps:get(props_to_return, Options1),
+    PropsToReturn1 = case effective_version(StoreId) of
+                         {ok, EffectiveMacVer} when EffectiveMacVer >= 2 ->
+                             PropsToReturn0;
+                         _ ->
+                             %% `delete_reason' was added in machine version
+                             %% 2. Also, previous versions didn't ignore
+                             %% unknown props_to_return and crashed.
+                             PropsToReturn0 -- [delete_reason]
+                     end,
+    Options2 = Options1#{props_to_return => PropsToReturn1},
+    Options2.
 
 -spec process_command(StoreId, Command, Options) -> Ret when
       StoreId :: khepri:store_id(),
@@ -1214,11 +1236,12 @@ can_skip_fence_preliminary_query(StoreId) ->
 
 -spec init(Params) -> State when
       Params :: machine_init_args(),
-      State :: state().
+      State :: khepri_machine_v0:state().
 %% @private
 
 init(Params) ->
-    %% Initialize the state.
+    %% Initialize the state. This function always return the oldest supported
+    %% state format.
     State = khepri_machine_v0:init(Params),
 
     %% Create initial "schema" if provided.
@@ -1742,7 +1765,7 @@ which_module(0) -> ?MODULE.
       EffectiveMacVer :: ra_machine:version().
 %% @doc Returns the effective state machine version of the local Ra server.
 
-effective_version(StoreId) ->
+effective_version(StoreId) when ?IS_KHEPRI_STORE_ID(StoreId) ->
     ThisNode = node(),
     RaServer = khepri_cluster:node_to_member(StoreId, ThisNode),
     case ra_counters:counters(RaServer, [effective_machine_version]) of
@@ -2392,6 +2415,17 @@ set_dedups(#khepri_machine{} = State, Dedups) ->
 set_dedups(State, _Dedups) ->
     State.
 
+-spec get_store_id(State) -> StoreId when
+      State :: khepri_machine:state(),
+      StoreId :: khepri:store_id().
+%% @doc Returns the store ID from the given state.
+%%
+%% @private
+
+get_store_id(State) ->
+    #config{store_id = StoreId} = get_config(State),
+    StoreId.
+
 -ifdef(TEST).
 -spec make_virgin_state(Params) -> State when
       Params :: khepri_machine:machine_init_args(),
diff --git a/src/khepri_tx.erl b/src/khepri_tx.erl
index a9a4d83c..78b5fa54 100644
--- a/src/khepri_tx.erl
+++ b/src/khepri_tx.erl
@@ -466,9 +466,11 @@ count(PathPattern) ->
 count(PathPattern, Options) ->
     PathPattern1 = khepri_tx_adv:path_from_string(PathPattern),
     {State, _SideEffects} = khepri_tx_adv:get_tx_state(),
+    StoreId = khepri_machine:get_store_id(State),
     Tree = khepri_machine:get_tree(State),
     Fun = fun khepri_tree:count_node_cb/3,
-    {_QueryOptions, TreeOptions} = khepri_machine:split_query_options(Options),
+    {_QueryOptions, TreeOptions} =
+    khepri_machine:split_query_options(StoreId, Options),
     TreeOptions1 = TreeOptions#{expect_specific_node => false},
     Ret = khepri_tree:fold(Tree, PathPattern1, Fun, 0, TreeOptions1),
     case Ret of
@@ -517,8 +519,10 @@ fold(PathPattern, Fun, Acc) ->
 fold(PathPattern, Fun, Acc, Options) ->
     PathPattern1 = khepri_tx_adv:path_from_string(PathPattern),
     {State, _SideEffects} = khepri_tx_adv:get_tx_state(),
+    StoreId = khepri_machine:get_store_id(State),
     Tree = khepri_machine:get_tree(State),
-    {_QueryOptions, TreeOptions} = khepri_machine:split_query_options(Options),
+    {_QueryOptions, TreeOptions} =
+    khepri_machine:split_query_options(StoreId, Options),
     TreeOptions1 = TreeOptions#{expect_specific_node => false},
     Ret = khepri_tree:fold(Tree, PathPattern1, Fun, Acc, TreeOptions1),
     case Ret of
diff --git a/src/khepri_tx_adv.erl b/src/khepri_tx_adv.erl
index 5ab4efa0..9e193aab 100644
--- a/src/khepri_tx_adv.erl
+++ b/src/khepri_tx_adv.erl
@@ -129,9 +129,11 @@ get_many(PathPattern, Options) ->
 
 do_get_many(PathPattern, Fun, Acc, Options) ->
     PathPattern1 = path_from_string(PathPattern),
-    {_QueryOptions, TreeOptions} = khepri_machine:split_query_options(Options),
     {State, _SideEffects} = get_tx_state(),
+    StoreId = khepri_machine:get_store_id(State),
     Tree = khepri_machine:get_tree(State),
+    {_QueryOptions, TreeOptions} =
+    khepri_machine:split_query_options(StoreId, Options),
     Ret = khepri_tree:fold(Tree, PathPattern1, Fun, Acc, TreeOptions),
     case Ret of
         {error, ?khepri_exception(_, _) = Exception} ->
@@ -210,14 +212,16 @@ put_many(PathPattern, Data, Options) ->
     ensure_updates_are_allowed(),
     PathPattern1 = path_from_string(PathPattern),
     Payload1 = khepri_payload:wrap(Data),
+    {State, _SideEffects} = get_tx_state(),
+    StoreId = khepri_machine:get_store_id(State),
     {_CommandOptions, TreeAndPutOptions} =
-    khepri_machine:split_command_options(Options),
+    khepri_machine:split_command_options(StoreId, Options),
     {TreeOptions, PutOptions} =
     khepri_machine:split_put_options(TreeAndPutOptions),
     %% TODO: Ensure `CommandOptions' is unset.
-    Fun = fun(State, SideEffects) ->
+    Fun = fun(State1, SideEffects) ->
                   khepri_machine:insert_or_update_node(
-                    State, PathPattern1, Payload1, PutOptions, TreeOptions,
+                    State1, PathPattern1, Payload1, PutOptions, TreeOptions,
                     SideEffects)
           end,
     handle_state_for_call(Fun).
@@ -401,13 +405,15 @@ delete_many(PathPattern) ->
 delete_many(PathPattern, Options) ->
     ensure_updates_are_allowed(),
     PathPattern1 = path_from_string(PathPattern),
+    {State, _SideEffects} = get_tx_state(),
+    StoreId = khepri_machine:get_store_id(State),
     {_CommandOptions, TreeOptions} =
-    khepri_machine:split_command_options(Options),
+    khepri_machine:split_command_options(StoreId, Options),
     %% TODO: Ensure `CommandOptions' is empty and `TreeOptions' doesn't
     %% contains put options.
-    Fun = fun(State, SideEffects) ->
+    Fun = fun(State1, SideEffects) ->
                   khepri_machine:delete_matching_nodes(
-                    State, PathPattern1, TreeOptions, SideEffects)
+                    State1, PathPattern1, TreeOptions, SideEffects)
           end,
     handle_state_for_call(Fun).