diff --git a/esphome/components/api/api_server.cpp b/esphome/components/api/api_server.cpp
index b1a5ee5d57..8b0130044e 100644
--- a/esphome/components/api/api_server.cpp
+++ b/esphome/components/api/api_server.cpp
@@ -421,7 +421,7 @@ void APIServer::handle_action_response(uint32_t call_id, bool success, const std
 #ifdef USE_API_HOMEASSISTANT_STATES
 // Helper to add subscription (reduces duplication)
 void APIServer::add_state_subscription_(const char *entity_id, const char *attribute,
-                                        std::function<void(std::string)> f, bool once) {
+                                        std::function<void(const std::string &)> f, bool once) {
   this->state_subs_.push_back(HomeAssistantStateSubscription{
       .entity_id = entity_id, .attribute = attribute, .callback = std::move(f), .once = once,
       // entity_id_dynamic_storage and attribute_dynamic_storage remain nullptr (no heap allocation)
@@ -430,7 +430,7 @@ void APIServer::add_state_subscription_(const char *entity_id, const char *attri
 
 // Helper to add subscription with heap-allocated strings (reduces duplication)
 void APIServer::add_state_subscription_(std::string entity_id, optional<std::string> attribute,
-                                        std::function<void(std::string)> f, bool once) {
+                                        std::function<void(const std::string &)> f, bool once) {
   HomeAssistantStateSubscription sub;
   // Allocate heap storage for the strings
   sub.entity_id_dynamic_storage = std::make_unique<std::string>(std::move(entity_id));
@@ -450,23 +450,23 @@ void APIServer::add_state_subscription_(std::string entity_id, optional<std::str
 
 // New const char* overload (for internal components - zero allocation)
 void APIServer::subscribe_home_assistant_state(const char *entity_id, const char *attribute,
-                                               std::function<void(std::string)> f) {
+                                               std::function<void(const std::string &)> f) {
   this->add_state_subscription_(entity_id, attribute, std::move(f), false);
 }
 
 void APIServer::get_home_assistant_state(const char *entity_id, const char *attribute,
-                                         std::function<void(std::string)> f) {
+                                         std::function<void(const std::string &)> f) {
   this->add_state_subscription_(entity_id, attribute, std::move(f), true);
 }
 
 // Existing std::string overload (for custom_api_device.h - heap allocation)
 void APIServer::subscribe_home_assistant_state(std::string entity_id, optional<std::string> attribute,
-                                               std::function<void(std::string)> f) {
+                                               std::function<void(const std::string &)> f) {
   this->add_state_subscription_(std::move(entity_id), std::move(attribute), std::move(f), false);
 }
 
 void APIServer::get_home_assistant_state(std::string entity_id, optional<std::string> attribute,
-                                         std::function<void(std::string)> f) {
+                                         std::function<void(const std::string &)> f) {
   this->add_state_subscription_(std::move(entity_id), std::move(attribute), std::move(f), true);
 }
 
diff --git a/esphome/components/api/api_server.h b/esphome/components/api/api_server.h
index ad7d8bf63d..dca9fbdffa 100644
--- a/esphome/components/api/api_server.h
+++ b/esphome/components/api/api_server.h
@@ -192,7 +192,7 @@ class APIServer : public Component,
   struct HomeAssistantStateSubscription {
     const char *entity_id;  // Pointer to flash (internal) or heap (external)
     const char *attribute;  // Pointer to flash or nullptr (nullptr means no attribute)
-    std::function<void(std::string)> callback;
+    std::function<void(const std::string &)> callback;
     bool once;
 
     // Dynamic storage for external components using std::string API (custom_api_device.h)
@@ -202,14 +202,16 @@ class APIServer : public Component,
   };
 
   // New const char* overload (for internal components - zero allocation)
-  void subscribe_home_assistant_state(const char *entity_id, const char *attribute, std::function<void(std::string)> f);
-  void get_home_assistant_state(const char *entity_id, const char *attribute, std::function<void(std::string)> f);
+  void subscribe_home_assistant_state(const char *entity_id, const char *attribute,
+                                      std::function<void(const std::string &)> f);
+  void get_home_assistant_state(const char *entity_id, const char *attribute,
+                                std::function<void(const std::string &)> f);
 
   // Existing std::string overload (for custom_api_device.h - heap allocation)
   void subscribe_home_assistant_state(std::string entity_id, optional<std::string> attribute,
-                                      std::function<void(std::string)> f);
+                                      std::function<void(const std::string &)> f);
   void get_home_assistant_state(std::string entity_id, optional<std::string> attribute,
-                                std::function<void(std::string)> f);
+                                std::function<void(const std::string &)> f);
 
   const std::vector<HomeAssistantStateSubscription> &get_state_subs() const;
 #endif
@@ -233,10 +235,10 @@ class APIServer : public Component,
 #endif  // USE_API_NOISE
 #ifdef USE_API_HOMEASSISTANT_STATES
   // Helper methods to reduce code duplication
-  void add_state_subscription_(const char *entity_id, const char *attribute, std::function<void(std::string)> f,
+  void add_state_subscription_(const char *entity_id, const char *attribute, std::function<void(const std::string &)> f,
                                bool once);
   void add_state_subscription_(std::string entity_id, optional<std::string> attribute,
-                               std::function<void(std::string)> f, bool once);
+                               std::function<void(const std::string &)> f, bool once);
 #endif  // USE_API_HOMEASSISTANT_STATES
   // Pointers and pointer-like types first (4 bytes each)
   std::unique_ptr<socket::Socket> socket_ = nullptr;
diff --git a/esphome/components/api/custom_api_device.h b/esphome/components/api/custom_api_device.h
index 5e9165326d..ee14063512 100644
--- a/esphome/components/api/custom_api_device.h
+++ b/esphome/components/api/custom_api_device.h
@@ -122,7 +122,7 @@ class CustomAPIDevice {
    *   subscribe_homeassistant_state(&CustomNativeAPI::on_state_changed, "climate.kitchen", "current_temperature");
    * }
    *
-   * void on_state_changed(std::string state) {
+   * void on_state_changed(const std::string &state) {
    *   // State of sensor.weather_forecast is `state`
    * }
    * ```
@@ -133,7 +133,7 @@ class CustomAPIDevice {
    * @param attribute The entity state attribute to track.
    */
   template<typename T>
-  void subscribe_homeassistant_state(void (T::*callback)(std::string), const std::string &entity_id,
+  void subscribe_homeassistant_state(void (T::*callback)(const std::string &), const std::string &entity_id,
                                      const std::string &attribute = "") {
     auto f = std::bind(callback, (T *) this, std::placeholders::_1);
     global_api_server->subscribe_home_assistant_state(entity_id, optional<std::string>(attribute), f);
@@ -148,7 +148,7 @@ class CustomAPIDevice {
    *   subscribe_homeassistant_state(&CustomNativeAPI::on_state_changed, "sensor.weather_forecast");
    * }
    *
-   * void on_state_changed(std::string entity_id, std::string state) {
+   * void on_state_changed(const std::string &entity_id, const std::string &state) {
    *   // State of `entity_id` is `state`
    * }
    * ```
@@ -159,14 +159,14 @@ class CustomAPIDevice {
    * @param attribute The entity state attribute to track.
    */
   template<typename T>
-  void subscribe_homeassistant_state(void (T::*callback)(std::string, std::string), const std::string &entity_id,
-                                     const std::string &attribute = "") {
+  void subscribe_homeassistant_state(void (T::*callback)(const std::string &, const std::string &),
+                                     const std::string &entity_id, const std::string &attribute = "") {
     auto f = std::bind(callback, (T *) this, entity_id, std::placeholders::_1);
     global_api_server->subscribe_home_assistant_state(entity_id, optional<std::string>(attribute), f);
   }
 #else
   template<typename T>
-  void subscribe_homeassistant_state(void (T::*callback)(std::string), const std::string &entity_id,
+  void subscribe_homeassistant_state(void (T::*callback)(const std::string &), const std::string &entity_id,
                                      const std::string &attribute = "") {
     static_assert(sizeof(T) == 0,
                   "subscribe_homeassistant_state() requires 'homeassistant_states: true' in the 'api:' section "
@@ -174,8 +174,8 @@ class CustomAPIDevice {
   }
 
   template<typename T>
-  void subscribe_homeassistant_state(void (T::*callback)(std::string, std::string), const std::string &entity_id,
-                                     const std::string &attribute = "") {
+  void subscribe_homeassistant_state(void (T::*callback)(const std::string &, const std::string &),
+                                     const std::string &entity_id, const std::string &attribute = "") {
     static_assert(sizeof(T) == 0,
                   "subscribe_homeassistant_state() requires 'homeassistant_states: true' in the 'api:' section "
                   "of your YAML configuration");