diff --git a/esphome/components/number/__init__.py b/esphome/components/number/__init__.py
index ea0c2d77f66..fc0893323be 100644
--- a/esphome/components/number/__init__.py
+++ b/esphome/components/number/__init__.py
@@ -174,6 +174,10 @@ NumberInRangeCondition = number_ns.class_(
 
 NumberMode = number_ns.enum("NumberMode")
 
+# Schema default that also matches the C++ initializer in number_traits.h; codegen
+# skips the setter when the config equals it.
+DEFAULT_MODE = "AUTO"
+
 NUMBER_MODES = {
     "AUTO": NumberMode.NUMBER_MODE_AUTO,
     "BOX": NumberMode.NUMBER_MODE_BOX,
@@ -216,7 +220,7 @@ _NUMBER_SCHEMA = (
                 CONF_UNIT_OF_MEASUREMENT, visibility=cv.Visibility.ADVANCED
             ): validate_unit_of_measurement,
             cv.Optional(
-                CONF_MODE, default="AUTO", visibility=cv.Visibility.ADVANCED
+                CONF_MODE, default=DEFAULT_MODE, visibility=cv.Visibility.ADVANCED
             ): cv.enum(NUMBER_MODES, upper=True),
             cv.Optional(
                 CONF_DEVICE_CLASS, visibility=cv.Visibility.ADVANCED
@@ -286,10 +290,10 @@ async def setup_number_core_(
     cg.add(var.traits.set_max_value(max_value))
     cg.add(var.traits.set_step(step))
 
-    # Only set if non-default to avoid bloating setup() function
-    # (mode_ is initialized to NUMBER_MODE_AUTO in the header)
-    if config[CONF_MODE] != NumberMode.NUMBER_MODE_AUTO:
-        cg.add(var.traits.set_mode(config[CONF_MODE]))
+    # Skip the setter when the config matches the C++ initializer (DEFAULT_MODE).
+    # The validated value is the enum key string, not the C++ enum expression.
+    if (mode := config[CONF_MODE]) != DEFAULT_MODE:
+        cg.add(var.traits.set_mode(mode))
 
     CORE.add_job(_build_number_automations, var, config)
 
diff --git a/esphome/components/number/number_traits.h b/esphome/components/number/number_traits.h
index f855813c9bf..3c7942b9a36 100644
--- a/esphome/components/number/number_traits.h
+++ b/esphome/components/number/number_traits.h
@@ -31,7 +31,7 @@ class NumberTraits {
   float min_value_ = NAN;
   float max_value_ = NAN;
   float step_ = NAN;
-  NumberMode mode_{NUMBER_MODE_AUTO};
+  NumberMode mode_{NUMBER_MODE_AUTO};  // Keep in sync with DEFAULT_MODE in __init__.py
 };
 
 }  // namespace esphome::number
diff --git a/tests/component_tests/number/__init__.py b/tests/component_tests/number/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/component_tests/number/config/mode.yaml b/tests/component_tests/number/config/mode.yaml
new file mode 100644
index 00000000000..b3eae34436f
--- /dev/null
+++ b/tests/component_tests/number/config/mode.yaml
@@ -0,0 +1,28 @@
+---
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+number:
+  - platform: template
+    id: auto_number
+    min_value: 0
+    max_value: 10
+    step: 1
+    optimistic: true
+  - platform: template
+    id: box_number
+    min_value: 0
+    max_value: 10
+    step: 1
+    mode: box
+    optimistic: true
+  - platform: template
+    id: explicit_auto_number
+    min_value: 0
+    max_value: 10
+    step: 1
+    mode: auto
+    optimistic: true
diff --git a/tests/component_tests/number/test_number.py b/tests/component_tests/number/test_number.py
new file mode 100644
index 00000000000..b33508602af
--- /dev/null
+++ b/tests/component_tests/number/test_number.py
@@ -0,0 +1,16 @@
+"""Tests for the number component codegen."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+
+def test_default_mode_is_not_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Mode auto is the C++ initializer, so only a non default mode is set."""
+    main_cpp = generate_main(component_config_path("mode.yaml"))
+
+    assert "auto_number->traits.set_mode(" not in main_cpp
+    assert "explicit_auto_number->traits.set_mode(" not in main_cpp
+    assert "box_number->traits.set_mode(number::NUMBER_MODE_BOX);" in main_cpp