diff --git a/esphome/components/api/api_server.cpp b/esphome/components/api/api_server.cpp
index 949262098f..461a8a8c3a 100644
--- a/esphome/components/api/api_server.cpp
+++ b/esphome/components/api/api_server.cpp
@@ -639,6 +639,14 @@ bool APIServer::teardown() {
 #define USE_API_ACTION_CALL_TIMEOUT_MS 30000  // NOLINT
 #endif
 
+// SSO-friendly action call key - hex format guarantees max 11 chars ("ac_ffffffff")
+// which fits in any std::string SSO buffer (typically 12-15 bytes)
+static inline std::string make_action_call_key(uint32_t id) {
+  char buf[12];
+  size_t len = snprintf(buf, sizeof(buf), "ac_%x", id);
+  return std::string(buf, len);
+}
+
 uint32_t APIServer::register_active_action_call(uint32_t client_call_id, APIConnection *conn) {
   uint32_t action_call_id = this->next_action_call_id_++;
   // Handle wraparound (skip 0 as it means "no call")
@@ -648,18 +656,17 @@ uint32_t APIServer::register_active_action_call(uint32_t client_call_id, APIConn
   this->active_action_calls_.push_back({action_call_id, client_call_id, conn});
 
   // Schedule automatic cleanup after timeout (client will have given up by then)
-  this->set_timeout(str_sprintf("action_call_%u", action_call_id), USE_API_ACTION_CALL_TIMEOUT_MS,
-                    [this, action_call_id]() {
-                      ESP_LOGD(TAG, "Action call %u timed out", action_call_id);
-                      this->unregister_active_action_call(action_call_id);
-                    });
+  this->set_timeout(make_action_call_key(action_call_id), USE_API_ACTION_CALL_TIMEOUT_MS, [this, action_call_id]() {
+    ESP_LOGD(TAG, "Action call %u timed out", action_call_id);
+    this->unregister_active_action_call(action_call_id);
+  });
 
   return action_call_id;
 }
 
 void APIServer::unregister_active_action_call(uint32_t action_call_id) {
   // Cancel the timeout for this action call
-  this->cancel_timeout(str_sprintf("action_call_%u", action_call_id));
+  this->cancel_timeout(make_action_call_key(action_call_id));
 
   // Swap-and-pop is more efficient than remove_if for unordered vectors
   for (size_t i = 0; i < this->active_action_calls_.size(); i++) {
@@ -676,7 +683,7 @@ void APIServer::unregister_active_action_calls_for_connection(APIConnection *con
   for (size_t i = 0; i < this->active_action_calls_.size();) {
     if (this->active_action_calls_[i].connection == conn) {
       // Cancel the timeout for this action call
-      this->cancel_timeout(str_sprintf("action_call_%u", this->active_action_calls_[i].action_call_id));
+      this->cancel_timeout(make_action_call_key(this->active_action_calls_[i].action_call_id));
 
       std::swap(this->active_action_calls_[i], this->active_action_calls_.back());
       this->active_action_calls_.pop_back();