diff --git a/esphome/components/climate/__init__.py b/esphome/components/climate/__init__.py
index 0f8bdb8ab0b..7c9002d6dc3 100644
--- a/esphome/components/climate/__init__.py
+++ b/esphome/components/climate/__init__.py
@@ -490,9 +490,9 @@ async def climate_control_to_code(config, action_id, template_arg, args):
 
     # All configured fields are folded into a single stateless lambda whose
     # constants live in flash; the action stores only a function pointer.
-    # `call_setter` is the ClimateCall method invoked in the lambda body —
-    # for custom_fan_mode/custom_preset this dispatches to the std::string
-    # overload of set_fan_mode/set_preset respectively.
+    # For custom_fan_mode/custom_preset the static-string path emits the
+    # (const char *, size_t) overload of set_fan_mode/set_preset to avoid
+    # constructing a std::string and calling runtime strlen.
     FIELDS = (
         (CONF_MODE, "set_mode", ClimateMode),
         (CONF_TARGET_TEMPERATURE, "set_target_temperature", cg.float_),
@@ -516,16 +516,20 @@ async def climate_control_to_code(config, action_id, template_arg, args):
             inner = await cg.process_lambda(value, args, return_type=type_)
             body_lines.append(f"call.{setter}(({inner})({fwd_args}));")
         elif type_ is cg.std_string:
-            # Static custom strings: emit a flash literal and pass the codegen-known
-            # length to skip the runtime strlen inside set_fan_mode/set_preset.
+            # Static custom strings: emit a flash literal and pass the
+            # UTF-8 byte length to skip the runtime strlen inside
+            # set_fan_mode/set_preset.
             literal = cg.safe_exp(value)
-            body_lines.append(f"call.{setter}({literal}, {len(value)});")
+            body_lines.append(
+                f"call.{setter}({literal}, {len(value.encode('utf-8'))});"
+            )
         else:
             body_lines.append(f"call.{setter}({cg.safe_exp(value)});")
 
+    # Match ControlAction::ApplyFn signature: const Ts &... for trigger args.
     apply_args = [
         (ClimateCall.operator("ref"), "call"),
-        *args,
+        *((t.operator("const").operator("ref"), n) for t, n in args),
     ]
     apply_lambda = LambdaExpression(
         ["\n".join(body_lines)],
diff --git a/esphome/components/climate/automation.h b/esphome/components/climate/automation.h
index b0353a41f9b..71d23fd6b6d 100644
--- a/esphome/components/climate/automation.h
+++ b/esphome/components/climate/automation.h
@@ -6,13 +6,13 @@
 namespace esphome::climate {
 
 // All configured fields are baked into a single stateless lambda whose
-// constants live in flash. The action only stores a function pointer
-// (4 bytes) plus the parent (4 bytes), regardless of how many fields the
-// user set. Trigger args are forwarded to the apply function so user
-// lambdas (e.g. `target_temperature: !lambda "return x;"`) keep working.
+// constants live in flash. The action only stores one function pointer
+// plus one parent pointer, regardless of how many fields the user set.
+// Trigger args are forwarded to the apply function so user lambdas
+// (e.g. `target_temperature: !lambda "return x;"`) keep working.
 template<typename... Ts> class ControlAction : public Action<Ts...> {
  public:
-  using ApplyFn = void (*)(ClimateCall &, Ts...);
+  using ApplyFn = void (*)(ClimateCall &, const Ts &...);
   ControlAction(Climate *climate, ApplyFn apply) : climate_(climate), apply_(apply) {}
 
   void play(const Ts &...x) override {
diff --git a/tests/integration/fixtures/climate_control_action.yaml b/tests/integration/fixtures/climate_control_action.yaml
index 596151ea516..1dd300fcc29 100644
--- a/tests/integration/fixtures/climate_control_action.yaml
+++ b/tests/integration/fixtures/climate_control_action.yaml
@@ -44,7 +44,7 @@ climate:
       max_temperature: 30 °C
 
 button:
-  # Test 1: mode only (mask 1)
+  # mode only
   - platform: template
     id: btn_mode
     name: "Set Mode Heat"
@@ -53,7 +53,7 @@ button:
           id: test_climate
           mode: HEAT
 
-  # Test 2: mode + low + high (mask 0b1101 = 13)
+  # mode + target_temperature_low + target_temperature_high
   - platform: template
     id: btn_mode_temps
     name: "Set Mode Temps"
@@ -64,7 +64,7 @@ button:
           target_temperature_low: 19.0 °C
           target_temperature_high: 23.0 °C
 
-  # Test 3: just target_temp_low (mask 0b0100 = 4)
+  # target_temperature_low only
   - platform: template
     id: btn_low_only
     name: "Set Low Only"
@@ -73,7 +73,7 @@ button:
           id: test_climate
           target_temperature_low: 17.5 °C
 
-  # Test 4: lambda for target_temperature_high (exercises lambda path)
+  # Lambda path: target_temperature_high computed at runtime
   - platform: template
     id: btn_lambda_high
     name: "Lambda High"
@@ -82,7 +82,7 @@ button:
           id: test_climate
           target_temperature_high: !lambda "return id(test_target_temp);"
 
-  # Test 5: turn off via mode
+  # mode only — turn off via mode
   - platform: template
     id: btn_off
     name: "Set Off"
diff --git a/tests/integration/test_climate_control_action.py b/tests/integration/test_climate_control_action.py
index 0070f9829e2..2b0293b2095 100644
--- a/tests/integration/test_climate_control_action.py
+++ b/tests/integration/test_climate_control_action.py
@@ -1,8 +1,8 @@
 """Integration test for climate ControlAction.
 
 Tests that climate.control automation actions work correctly with the
-per-instance bitmask field storage. Exercises multiple field combinations
-to cover different bitmask variants and the lambda path.
+single stateless apply lambda/function pointer implementation. Exercises
+multiple field combinations and the lambda path.
 """
 
 from __future__ import annotations
@@ -61,24 +61,24 @@ async def test_climate_control_action(
             client.button_command(btn.key)
             return await wait_for_climate_state()
 
-        # Test 1: mode only (mask 1) — set HEAT
+        # mode only — set HEAT
         state = await press_and_wait("Set Mode Heat")
         assert state.mode == ClimateMode.HEAT
 
-        # Test 2: mode + low + high (mask 13) — HEAT_COOL with both temps
+        # mode + target_temperature_low + target_temperature_high
         state = await press_and_wait("Set Mode Temps")
         assert state.mode == ClimateMode.HEAT_COOL
         assert state.target_temperature_low == pytest.approx(19.0, abs=0.5)
         assert state.target_temperature_high == pytest.approx(23.0, abs=0.5)
 
-        # Test 3: low only (mask 4)
+        # target_temperature_low only
         state = await press_and_wait("Set Low Only")
         assert state.target_temperature_low == pytest.approx(17.5, abs=0.5)
 
-        # Test 4: lambda high — global is 21.5
+        # lambda path: target_temperature_high computed at runtime
         state = await press_and_wait("Lambda High")
         assert state.target_temperature_high == pytest.approx(21.5, abs=0.5)
 
-        # Test 5: turn off via mode (mask 1)
+        # mode only — turn off via mode
         state = await press_and_wait("Set Off")
         assert state.mode == ClimateMode.OFF