diff --git a/packages/home_capabilities/thermostat.py b/packages/home_capabilities/thermostat.py
index 9b4016a..24a0eba 100644
--- a/packages/home_capabilities/thermostat.py
+++ b/packages/home_capabilities/thermostat.py
@@ -16,16 +16,16 @@ class ThermostatState(BaseModel):
     Thermostat state model with validation.
     
     Attributes:
-        mode: Operating mode (off, heat, auto)
+        mode: Operating mode (off, heat, auto) - optional for SET commands
         target: Target temperature in °C [5.0..30.0]
         current: Current temperature in °C (optional in SET, required in STATE)
         battery: Battery level 0-100% (optional)
         window_open: Window open detection (optional)
     """
     
-    mode: Literal["off", "heat", "auto"] = Field(
-        ...,
-        description="Operating mode of the thermostat"
+    mode: Literal["off", "heat", "auto"] | None = Field(
+        None,
+        description="Operating mode of the thermostat (optional for SET commands)"
     )
     
     target: float | Decimal = Field(