diff --git a/esphome/components/api/api.proto b/esphome/components/api/api.proto
index d55cf10c47d..41ece9275fd 100644
--- a/esphome/components/api/api.proto
+++ b/esphome/components/api/api.proto
@@ -403,6 +403,9 @@ message WizardCapabilities {
 message SendspinCapabilities {
   // Bitmask of the Sendspin features this device supports
   uint32 feature_flags = 1;
+  // The Sendspin client_id: base64url of the client's static public key, 43 characters.
+  // Empty until the Sendspin client has started once since boot.
+  string client_id = 2 [(max_data_length) = 43];
 }
 
 message DeviceCapabilitiesResponse {
diff --git a/esphome/components/api/api_connection.cpp b/esphome/components/api/api_connection.cpp
index ca2397b5d78..bcb6486a84d 100644
--- a/esphome/components/api/api_connection.cpp
+++ b/esphome/components/api/api_connection.cpp
@@ -2131,6 +2131,7 @@ bool APIConnection::send_device_capabilities_response_() {
 #endif
 #if defined(USE_SENDSPIN) && defined(USE_ESP_IDF)
   resp.sendspin.feature_flags = sendspin_::global_sendspin_hub->get_feature_flags();
+  resp.sendspin.client_id = sendspin_::global_sendspin_hub->get_client_id();
 #endif
   return this->send_message(resp);
 }
diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index bcfa86763a1..227af11bc08 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -310,12 +310,14 @@ uint32_t WizardCapabilities::calc_size_msg(const void *self) {
 uint8_t *SendspinCapabilities::encode_msg(const void *self, uint8_t *__restrict__ pos PROTO_ENCODE_DEBUG_PARAM) {
   const auto &msg = *static_cast<const SendspinCapabilities *>(self);
   pos = ProtoEncode::encode_uint32(pos PROTO_ENCODE_DEBUG_ARG, 1, msg.feature_flags);
+  pos = ProtoEncode::encode_string(pos PROTO_ENCODE_DEBUG_ARG, 2, msg.client_id);
   return pos;
 }
 uint32_t SendspinCapabilities::calc_size_msg(const void *self) {
   const auto &msg = *static_cast<const SendspinCapabilities *>(self);
   uint32_t size = 0;
   size += ProtoSize::calc_uint32(1, msg.feature_flags);
+  size += !msg.client_id.empty() ? 2 + msg.client_id.size() : 0;
   return size;
 }
 #endif
diff --git a/esphome/components/api/api_pb2.h b/esphome/components/api/api_pb2.h
index 7c8082a8c7c..7ec8955610c 100644
--- a/esphome/components/api/api_pb2.h
+++ b/esphome/components/api/api_pb2.h
@@ -750,6 +750,7 @@ class WizardCapabilities final : public ProtoMessage {
 class SendspinCapabilities final : public ProtoMessage {
  public:
   uint32_t feature_flags{0};
+  StringRef client_id{nullptr, 0};  // null until set, encode only
   static uint8_t *encode_msg(const void *self, uint8_t *pos PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer.get_pos() PROTO_ENCODE_DEBUG_ARG);
diff --git a/esphome/components/api/api_pb2_dump.cpp b/esphome/components/api/api_pb2_dump.cpp
index ec224c46e29..23ce6319ed1 100644
--- a/esphome/components/api/api_pb2_dump.cpp
+++ b/esphome/components/api/api_pb2_dump.cpp
@@ -1119,6 +1119,7 @@ const char *WizardCapabilities::dump_to(DumpBuffer &out) const {
 const char *SendspinCapabilities::dump_to(DumpBuffer &out) const {
   MessageDumpHelper helper(out, ESPHOME_PSTR("SendspinCapabilities"));
   dump_field(out, ESPHOME_PSTR("feature_flags"), this->feature_flags);
+  dump_field(out, ESPHOME_PSTR("client_id"), this->client_id);
   return out.c_str();
 }
 #endif
diff --git a/esphome/components/sendspin/sendspin_hub.cpp b/esphome/components/sendspin/sendspin_hub.cpp
index 8b5eaeeed23..701676503f4 100644
--- a/esphome/components/sendspin/sendspin_hub.cpp
+++ b/esphome/components/sendspin/sendspin_hub.cpp
@@ -243,6 +243,14 @@ std::optional<std::string> SendspinHub::get_pairing_token() const {
   return this->client_->pairing_token();
 }
 
+// THREAD CONTEXT: Main loop
+StringRef SendspinHub::get_client_id() const {
+  if (this->client_ == nullptr) {
+    return StringRef();
+  }
+  return StringRef(this->client_->client_id());
+}
+
 // THREAD CONTEXT: Main loop (invoked from codegen before setup(), or from Sendspin components)
 void SendspinHub::set_unpaired_access_enabled(bool enabled) {
   this->unpaired_access_ = enabled;
diff --git a/esphome/components/sendspin/sendspin_hub.h b/esphome/components/sendspin/sendspin_hub.h
index cd8d0d0afaf..23c60d215b6 100644
--- a/esphome/components/sendspin/sendspin_hub.h
+++ b/esphome/components/sendspin/sendspin_hub.h
@@ -198,6 +198,12 @@ class SendspinHub final : public Component,
   /// started once; it stays available after the client stops. Main loop only.
   std::optional<std::string> get_pairing_token() const;
 
+  /// @brief Returns the Sendspin client_id: base64url of the client's static public key.
+  ///
+  /// Empty until the client has started once; it stays set after the client stops. The returned StringRef points into
+  /// the client's string, which start() may rewrite, so do not keep it past the current call. Main loop only.
+  StringRef get_client_id() const;
+
   /// @brief Sets the device information reported to the server in the `client/hello` message.
   ///
   /// Each takes a pointer to a string literal emitted by codegen, so it must stay valid for the
diff --git a/tests/unit_tests/components/api/test_api_proto.py b/tests/unit_tests/components/api/test_api_proto.py
index ca3c0ce7b58..68e3cab2a21 100644
--- a/tests/unit_tests/components/api/test_api_proto.py
+++ b/tests/unit_tests/components/api/test_api_proto.py
@@ -71,7 +71,7 @@ NEW_CAPABILITY_FIELDS: dict[str, dict[str, int]] = {
         "sendspin": 6,
     },
     "WizardCapabilities": {"configured": 1},
-    "SendspinCapabilities": {"feature_flags": 1},
+    "SendspinCapabilities": {"feature_flags": 1, "client_id": 2},
     "BluetoothProxyCapabilities": {
         "feature_flags": 1,
         "mac_address": 2,