diff --git a/docs/PORT_CONNECTION_RULES.md b/docs/PORT_CONNECTION_RULES.md
index 61a964875..23f2523d1 100644
--- a/docs/PORT_CONNECTION_RULES.md
+++ b/docs/PORT_CONNECTION_RULES.md
@@ -179,6 +179,12 @@ InputPort<Point2D>("pointE", R"(json:{"x":9,"y":10})", "description")
 
 **Test reference:** `gtest_ports.cpp`
 
+## SubTree Model Defaults with `_autoremap`
+
+A `<SubTree>` entry in `<TreeNodesModel>` can declare an `input_port` with a literal `default`. With `_autoremap="true"`, that default is applied **only if no entry with that name exists in the parent blackboard chain at the moment the tree is created**. If the key is missing at that point, the literal default is stored in the SubTree's own blackboard and shadows the parent: a value written to the parent later (for instance by a `<Script>` that runs before the SubTree) is **not** seen by the SubTree. To make the parent value win, create the key in the blackboard before `createTree()` (e.g. `bb->set("in_value", 7)`), or remap the port explicitly (`in_value="{in_value}"`). Output and bidirectional ports and `{key}` defaults are not affected.
+
+**Test reference:** `gtest_subtree.cpp` - `SubtreeModelDefaultWithAutoremap`, `SubtreeModelDefaultWithAutoremapParentWins`, `SubtreeModelDefaultWithAutoremapCreationTimeRule` tests
+
 ## Validation Timeline
 
 ### At Tree Creation (XML Parsing)
diff --git a/src/xml_parsing.cpp b/src/xml_parsing.cpp
index 40e773742..5663c7889 100644
--- a/src/xml_parsing.cpp
+++ b/src/xml_parsing.cpp
@@ -1208,6 +1208,18 @@ void BT::XMLParser::PImpl::recursivelyCreateSubtree(
         for(const auto& [port_name, port_info] : subtree_model_ports)
         {
           auto it = subtree_remapping.find(port_name);
+          const auto& default_value = port_info.defaultValueString();
+          // _autoremap shares the port with the parent key of the same name; if
+          // that key doesn't exist (yet), an input port gets its literal default
+          // (#1271). NOTE: checked at creation time, so a parent key created
+          // later (e.g. by a Script) is shadowed by the default.
+          if(it == subtree_remapping.end() && do_autoremap &&
+             port_info.direction() == PortDirection::INPUT && !default_value.empty() &&
+             !TreeNode::isBlackboardPointer(default_value) &&
+             !new_bb->getEntry(port_name))
+          {
+            subtree_remapping.insert({ port_name, default_value });
+          }
           // don't override existing remapping
           if(it == subtree_remapping.end() && !do_autoremap)
           {
diff --git a/tests/gtest_subtree.cpp b/tests/gtest_subtree.cpp
index 0aa5849c7..56cf1fbeb 100644
--- a/tests/gtest_subtree.cpp
+++ b/tests/gtest_subtree.cpp
@@ -595,6 +595,133 @@ TEST(SubTree, SubtreeModels)
   tree.tickWhileRunning();
 }
 
+TEST(SubTree, SubtreeModelDefault)
+{
+  // clang-format off
+
+  static const char* xml_text = R"(
+<root main_tree_to_execute = "MainTree" BTCPP_format="4">
+  <TreeNodesModel>
+    <SubTree ID="MySub">
+      <input_port name="in_value" default="42"/>
+    </SubTree>
+  </TreeNodesModel>
+
+  <BehaviorTree ID="MainTree">
+    <Sequence>
+      <SubTree ID="MySub" />
+    </Sequence>
+  </BehaviorTree>
+
+  <BehaviorTree ID="MySub">
+    <Sequence>
+      <ScriptCondition code="in_value==42" />
+    </Sequence>
+  </BehaviorTree>
+</root>
+ )";
+
+  // clang-format on
+
+  BehaviorTreeFactory factory;
+  auto tree = factory.createTreeFromText(xml_text);
+  tree.tickWhileRunning();
+}
+
+TEST(SubTree, SubtreeModelDefaultWithAutoremap)
+{
+  // clang-format off
+
+  static const char* xml_text = R"(
+<root main_tree_to_execute = "MainTree" BTCPP_format="4">
+  <TreeNodesModel>
+    <SubTree ID="MySub">
+      <input_port name="in_value" default="42"/>
+    </SubTree>
+  </TreeNodesModel>
+
+  <BehaviorTree ID="MainTree">
+    <Sequence>
+      <SubTree ID="MySub" _autoremap="true" />
+    </Sequence>
+  </BehaviorTree>
+
+  <BehaviorTree ID="MySub">
+    <Sequence>
+      <ScriptCondition code="in_value==42" />
+    </Sequence>
+  </BehaviorTree>
+</root>
+ )";
+
+  // clang-format on
+
+  BehaviorTreeFactory factory;
+  auto tree = factory.createTreeFromText(xml_text);
+  tree.tickWhileRunning();
+}
+
+// With _autoremap, a parent key of the same name wins over the model default
+// (#1271), and the default stays local to the SubTree.
+TEST(SubTree, SubtreeModelDefaultWithAutoremapParentWins)
+{
+  static const char* xml_text = R"(
+<root main_tree_to_execute="MainTree" BTCPP_format="4">
+  <TreeNodesModel>
+    <SubTree ID="MySub">
+      <input_port name="in_value" default="42"/>
+      <input_port name="other" default="43"/>
+    </SubTree>
+  </TreeNodesModel>
+
+  <BehaviorTree ID="MainTree">
+    <SubTree ID="MySub" _autoremap="true" />
+  </BehaviorTree>
+
+  <BehaviorTree ID="MySub">
+    <ScriptCondition code="in_value==7 &amp;&amp; other==43" />
+  </BehaviorTree>
+</root>)";
+
+  BehaviorTreeFactory factory;
+  auto root_bb = Blackboard::create();
+  root_bb->set("in_value", 7);
+  auto tree = factory.createTreeFromText(xml_text, root_bb);
+  EXPECT_EQ(tree.tickWhileRunning(), NodeStatus::SUCCESS);
+  EXPECT_FALSE(root_bb->getEntry("other"));
+}
+
+// Deliberate creation-time rule (#1271): the model default is applied only if no
+// entry named "in_value" exists in the parent blackboard chain when the tree is
+// CREATED. A key written later (here by a Script) does not win; to make the parent
+// value win, set the key in the blackboard before createTree (see test above).
+TEST(SubTree, SubtreeModelDefaultWithAutoremapCreationTimeRule)
+{
+  static const char* xml_text = R"(
+<root main_tree_to_execute="MainTree" BTCPP_format="4">
+  <TreeNodesModel>
+    <SubTree ID="MySub">
+      <input_port name="in_value" default="42"/>
+    </SubTree>
+  </TreeNodesModel>
+
+  <BehaviorTree ID="MainTree">
+    <Sequence>
+      <Script code="in_value:=7" />
+      <SubTree ID="MySub" _autoremap="true" />
+    </Sequence>
+  </BehaviorTree>
+
+  <BehaviorTree ID="MySub">
+    <ScriptCondition code="in_value==42" />
+  </BehaviorTree>
+</root>)";
+
+  BehaviorTreeFactory factory;
+  auto tree = factory.createTreeFromText(xml_text);
+  EXPECT_EQ(tree.tickWhileRunning(), NodeStatus::SUCCESS);
+}
+
 class PrintToConsole : public BT::SyncActionNode
 {
 public: