[core] Remove object_id RAM storage - no longer in hot path after #12627 (#12631)

esphome/core/entity_base.cpp

@@ -9,7 +9,8 @@ static const char *const TAG = "entity_base";
 
 // Entity Name
 const StringRef &EntityBase::get_name() const { return this->name_; }
-void EntityBase::set_name(const char *name) {
+void EntityBase::set_name(const char *name) { this->set_name(name, 0); }
+void EntityBase::set_name(const char *name, uint32_t object_id_hash) {
   this->name_ = StringRef(name);
   if (this->name_.empty()) {
 #ifdef USE_DEVICES
@@ -18,11 +19,29 @@ void EntityBase::set_name(const char *name) {
     } else
 #endif
     {
-      this->name_ = StringRef(App.get_friendly_name());
+      // Bug-for-bug compatibility with OLD behavior:
+      // - With MAC suffix: OLD code used App.get_friendly_name() directly (no fallback)
+      // - Without MAC suffix: OLD code used pre-computed object_id with fallback to device name
+      const std::string &friendly = App.get_friendly_name();
+      if (App.is_name_add_mac_suffix_enabled()) {
+        // MAC suffix enabled - use friendly_name directly (even if empty) for compatibility
+        this->name_ = StringRef(friendly);
+      } else {
+        // No MAC suffix - fallback to device name if friendly_name is empty
+        this->name_ = StringRef(!friendly.empty() ? friendly : App.get_name());
+      }
     }
     this->flags_.has_own_name = false;
+    // Dynamic name - must calculate hash at runtime
+    this->calc_object_id_();
   } else {
     this->flags_.has_own_name = true;
+    // Static name - use pre-computed hash if provided
+    if (object_id_hash != 0) {
+      this->object_id_hash_ = object_id_hash;
+    } else {
+      this->calc_object_id_();
+    }
   }
 }
 
@@ -45,69 +64,30 @@ void EntityBase::set_icon(const char *icon) {
 #endif
 }
 
-// Check if the object_id is dynamic (changes with MAC suffix)
-bool EntityBase::is_object_id_dynamic_() const {
-  return !this->flags_.has_own_name && App.is_name_add_mac_suffix_enabled();
-}
-
-// Entity Object ID
+// Entity Object ID - computed on-demand from name
 std::string EntityBase::get_object_id() const {
-  // Check if `App.get_friendly_name()` is constant or dynamic.
-  if (this->is_object_id_dynamic_()) {
-    // `App.get_friendly_name()` is dynamic.
-    return str_sanitize(str_snake_case(App.get_friendly_name()));
-  }
-  // `App.get_friendly_name()` is constant.
-  return this->object_id_c_str_ == nullptr ? "" : this->object_id_c_str_;
-}
-void EntityBase::set_object_id(const char *object_id) {
-  this->object_id_c_str_ = object_id;
-  this->calc_object_id_();
-}
-
-void EntityBase::set_name_and_object_id(const char *name, const char *object_id) {
-  this->set_name(name);
-  this->object_id_c_str_ = object_id;
-  this->calc_object_id_();
-}
-
-// Calculate Object ID Hash from Entity Name
-void EntityBase::calc_object_id_() {
   char buf[OBJECT_ID_MAX_LEN];
-  StringRef object_id = this->get_object_id_to(buf);
-  this->object_id_hash_ = fnv1_hash(object_id.c_str());
+  size_t len = this->write_object_id_to(buf, sizeof(buf));
+  return std::string(buf, len);
 }
 
-// Format dynamic object_id: sanitized snake_case of friendly_name
-static size_t format_dynamic_object_id(char *buf, size_t buf_size) {
-  const std::string &name = App.get_friendly_name();
-  size_t len = std::min(name.size(), buf_size - 1);
-  for (size_t i = 0; i < len; i++) {
-    buf[i] = to_sanitized_char(to_snake_case_char(name[i]));
-  }
-  buf[len] = '\0';
-  return len;
+// Calculate Object ID Hash directly from name using snake_case + sanitize
+void EntityBase::calc_object_id_() {
+  this->object_id_hash_ = fnv1_hash_object_id(this->name_.c_str(), this->name_.size());
 }
 
 size_t EntityBase::write_object_id_to(char *buf, size_t buf_size) const {
-  if (this->is_object_id_dynamic_()) {
-    return format_dynamic_object_id(buf, buf_size);
+  size_t len = std::min(this->name_.size(), buf_size - 1);
+  for (size_t i = 0; i < len; i++) {
+    buf[i] = to_sanitized_char(to_snake_case_char(this->name_[i]));
   }
-  const char *src = this->object_id_c_str_ == nullptr ? "" : this->object_id_c_str_;
-  size_t len = strlen(src);
-  if (len >= buf_size)
-    len = buf_size - 1;
-  memcpy(buf, src, len);
   buf[len] = '\0';
   return len;
 }
 
 StringRef EntityBase::get_object_id_to(std::span<char, OBJECT_ID_MAX_LEN> buf) const {
-  if (this->is_object_id_dynamic_()) {
-    size_t len = format_dynamic_object_id(buf.data(), buf.size());
-    return StringRef(buf.data(), len);
-  }
-  return this->object_id_c_str_ == nullptr ? StringRef() : StringRef(this->object_id_c_str_);
+  size_t len = this->write_object_id_to(buf.data(), buf.size());
+  return StringRef(buf.data(), len);
 }
 
 uint32_t EntityBase::get_object_id_hash() { return this->object_id_hash_; }

esphome/core/entity_base.h

@@ -28,6 +28,9 @@ class EntityBase {
   // Get/set the name of this Entity
   const StringRef &get_name() const;
   void set_name(const char *name);
+  /// Set name with pre-computed object_id hash (avoids runtime hash calculation)
+  /// Use hash=0 for dynamic names that need runtime calculation
+  void set_name(const char *name, uint32_t object_id_hash);
 
   // Get whether this Entity has its own name or it should use the device friendly_name.
   bool has_own_name() const { return this->flags_.has_own_name; }
@@ -43,10 +46,6 @@ class EntityBase {
                 "which will remain available longer. get_object_id() will be removed in 2026.7.0",
                 "2025.12.0")
   std::string get_object_id() const;
-  void set_object_id(const char *object_id);
-
-  // Set both name and object_id in one call (reduces generated code size)
-  void set_name_and_object_id(const char *name, const char *object_id);
 
   // Get the unique Object ID of this Entity
   uint32_t get_object_id_hash();
@@ -142,11 +141,7 @@ class EntityBase {
  protected:
   void calc_object_id_();
 
-  /// Check if the object_id is dynamic (changes with MAC suffix)
-  bool is_object_id_dynamic_() const;
-
   StringRef name_;
-  const char *object_id_c_str_{nullptr};
 #ifdef USE_ENTITY_ICON
   const char *icon_c_str_{nullptr};
 #endif

esphome/core/entity_helpers.py

@@ -15,7 +15,7 @@ from esphome.const import (
 from esphome.core import CORE, ID
 from esphome.cpp_generator import MockObj, add, get_variable
 import esphome.final_validate as fv
-from esphome.helpers import sanitize, snake_case
+from esphome.helpers import fnv1_hash_object_id, sanitize, snake_case
 from esphome.types import ConfigType, EntityMetadata
 
 _LOGGER = logging.getLogger(__name__)
@@ -75,34 +75,18 @@ async def setup_entity(var: MockObj, config: ConfigType, platform: str) -> None:
         config: Configuration dictionary containing entity settings
         platform: The platform name (e.g., "sensor", "binary_sensor")
     """
-    # Get device info
-    device_name: str | None = None
-    device_id_obj: ID | None
+    # Get device info if configured
     if device_id_obj := config.get(CONF_DEVICE_ID):
         device: MockObj = await get_variable(device_id_obj)
         add(var.set_device(device))
-        # Get device name for object ID calculation
-        device_name = device_id_obj.id
 
-    # Calculate base object_id using the same logic as C++
-    # This must match the C++ behavior in esphome/core/entity_base.cpp
-    base_object_id = get_base_entity_object_id(
-        config[CONF_NAME], CORE.friendly_name, device_name
-    )
-
-    if not config[CONF_NAME]:
-        _LOGGER.debug(
-            "Entity has empty name, using '%s' as object_id base", base_object_id
-        )
-
-    # Set both name and object_id in one call to reduce generated code size
-    add(var.set_name_and_object_id(config[CONF_NAME], base_object_id))
-    _LOGGER.debug(
-        "Setting object_id '%s' for entity '%s' on platform '%s'",
-        base_object_id,
-        config[CONF_NAME],
-        platform,
-    )
+    # Set the entity name with pre-computed object_id hash
+    # For named entities: pre-compute hash from entity name
+    # For empty-name entities: pass 0, C++ calculates hash at runtime from
+    # device name, friendly_name, or app name (bug-for-bug compatibility)
+    entity_name = config[CONF_NAME]
+    object_id_hash = fnv1_hash_object_id(entity_name) if entity_name else 0
+    add(var.set_name(entity_name, object_id_hash))
     # Only set disabled_by_default if True (default is False)
     if config[CONF_DISABLED_BY_DEFAULT]:
         add(var.set_disabled_by_default(True))

esphome/core/helpers.h

@@ -529,6 +529,20 @@ constexpr char to_sanitized_char(char c) {
 /// Sanitizes the input string by removing all characters but alphanumerics, dashes and underscores.
 std::string str_sanitize(const std::string &str);
 
+/// Calculate FNV-1 hash of a string while applying snake_case + sanitize transformations.
+/// This computes object_id hashes directly from names without creating an intermediate buffer.
+/// IMPORTANT: Must match Python fnv1_hash_object_id() in esphome/helpers.py.
+/// If you modify this function, update the Python version and tests in both places.
+inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
+  uint32_t hash = FNV1_OFFSET_BASIS;
+  for (size_t i = 0; i < len; i++) {
+    hash *= FNV1_PRIME;
+    // Apply snake_case (space->underscore, uppercase->lowercase) then sanitize
+    hash ^= static_cast<uint8_t>(to_sanitized_char(to_snake_case_char(str[i])));
+  }
+  return hash;
+}
+
 /// snprintf-like function returning std::string of maximum length \p len (excluding null terminator).
 std::string __attribute__((format(printf, 1, 3))) str_snprintf(const char *fmt, size_t len, ...);
 

esphome/helpers.py

@@ -35,6 +35,10 @@ IS_MACOS = platform.system() == "Darwin"
 IS_WINDOWS = platform.system() == "Windows"
 IS_LINUX = platform.system() == "Linux"
 
+# FNV-1 hash constants (must match C++ in esphome/core/helpers.h)
+FNV1_OFFSET_BASIS = 2166136261
+FNV1_PRIME = 16777619
+
 
 def ensure_unique_string(preferred_string, current_strings):
     test_string = preferred_string
@@ -49,8 +53,17 @@ def ensure_unique_string(preferred_string, current_strings):
     return test_string
 
 
+def fnv1_hash(string: str) -> int:
+    """FNV-1 32-bit hash function (multiply then XOR)."""
+    hash_value = FNV1_OFFSET_BASIS
+    for char in string:
+        hash_value = (hash_value * FNV1_PRIME) & 0xFFFFFFFF
+        hash_value ^= ord(char)
+    return hash_value
+
+
 def fnv1a_32bit_hash(string: str) -> int:
-    """FNV-1a 32-bit hash function.
+    """FNV-1a 32-bit hash function (XOR then multiply).
 
     Note: This uses 32-bit hash instead of 64-bit for several reasons:
     1. ESPHome targets 32-bit microcontrollers with limited RAM (often <320KB)
@@ -63,13 +76,22 @@ def fnv1a_32bit_hash(string: str) -> int:
     a handful of area_ids and device_ids (typically <10 areas and <100
     devices), making collisions virtually impossible.
     """
-    hash_value = 2166136261
+    hash_value = FNV1_OFFSET_BASIS
     for char in string:
         hash_value ^= ord(char)
-        hash_value = (hash_value * 16777619) & 0xFFFFFFFF
+        hash_value = (hash_value * FNV1_PRIME) & 0xFFFFFFFF
     return hash_value
 
 
+def fnv1_hash_object_id(name: str) -> int:
+    """Compute FNV-1 hash of name with snake_case + sanitize transformations.
+
+    IMPORTANT: Must produce same result as C++ fnv1_hash_object_id() in helpers.h.
+    Used for pre-computing entity object_id hashes at code generation time.
+    """
+    return fnv1_hash(sanitize(snake_case(name)))
+
+
 def strip_accents(value: str) -> str:
     """Remove accents from a string."""
     import unicodedata

tests/component_tests/binary_sensor/test_binary_sensor.py

@@ -29,7 +29,7 @@ def test_binary_sensor_sets_mandatory_fields(generate_main):
     )
 
     # Then
-    assert 'bs_1->set_name_and_object_id("test bs1", "test_bs1");' in main_cpp
+    assert 'bs_1->set_name("test bs1",' in main_cpp
     assert "bs_1->set_pin(" in main_cpp
 
 

tests/component_tests/button/test_button.py

@@ -26,7 +26,7 @@ def test_button_sets_mandatory_fields(generate_main):
     main_cpp = generate_main("tests/component_tests/button/test_button.yaml")
 
     # Then
-    assert 'wol_1->set_name_and_object_id("wol_test_1", "wol_test_1");' in main_cpp
+    assert 'wol_1->set_name("wol_test_1",' in main_cpp
     assert "wol_2->set_macaddr(18, 52, 86, 120, 144, 171);" in main_cpp
 
 

tests/component_tests/text/test_text.py

@@ -25,7 +25,7 @@ def test_text_sets_mandatory_fields(generate_main):
     main_cpp = generate_main("tests/component_tests/text/test_text.yaml")
 
     # Then
-    assert 'it_1->set_name_and_object_id("test 1 text", "test_1_text");' in main_cpp
+    assert 'it_1->set_name("test 1 text",' in main_cpp
 
 
 def test_text_config_value_internal_set(generate_main):

tests/component_tests/text_sensor/test_text_sensor.py

@@ -25,18 +25,9 @@ def test_text_sensor_sets_mandatory_fields(generate_main):
     main_cpp = generate_main("tests/component_tests/text_sensor/test_text_sensor.yaml")
 
     # Then
-    assert (
-        'ts_1->set_name_and_object_id("Template Text Sensor 1", "template_text_sensor_1");'
-        in main_cpp
-    )
-    assert (
-        'ts_2->set_name_and_object_id("Template Text Sensor 2", "template_text_sensor_2");'
-        in main_cpp
-    )
-    assert (
-        'ts_3->set_name_and_object_id("Template Text Sensor 3", "template_text_sensor_3");'
-        in main_cpp
-    )
+    assert 'ts_1->set_name("Template Text Sensor 1",' in main_cpp
+    assert 'ts_2->set_name("Template Text Sensor 2",' in main_cpp
+    assert 'ts_3->set_name("Template Text Sensor 3",' in main_cpp
 
 
 def test_text_sensor_config_value_internal_set(generate_main):

tests/integration/conftest.py

@@ -51,6 +51,9 @@ if platform.system() == "Windows":
 
 import pty  # not available on Windows
 
+# Register assert rewrite for entity_utils so assertions have proper error messages
+pytest.register_assert_rewrite("tests.integration.entity_utils")
+
 
 def _get_platformio_env(cache_dir: Path) -> dict[str, str]:
     """Get environment variables for PlatformIO with shared cache."""

tests/integration/entity_utils.py

@@ -0,0 +1,145 @@
+"""Utilities for computing entity object_id in integration tests.
+
+This module contains the algorithm that aioesphomeapi will use to compute
+object_id client-side from API data.
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from esphome.helpers import fnv1_hash_object_id, sanitize, snake_case
+
+if TYPE_CHECKING:
+    from aioesphomeapi import DeviceInfo, EntityInfo
+
+
+def compute_object_id(name: str) -> str:
+    """Compute object_id from name using snake_case + sanitize."""
+    return sanitize(snake_case(name))
+
+
+def infer_name_add_mac_suffix(device_info: DeviceInfo) -> bool:
+    """Infer name_add_mac_suffix from device name ending with MAC suffix."""
+    mac_suffix = device_info.mac_address.replace(":", "")[-6:].lower()
+    return device_info.name.endswith(f"-{mac_suffix}")
+
+
+def _get_name_for_object_id(
+    entity: EntityInfo,
+    device_info: DeviceInfo,
+    device_id_to_name: dict[int, str],
+) -> str:
+    """Get the name used for object_id computation.
+
+    This is the algorithm that aioesphomeapi will use to determine which
+    name to use for computing object_id client-side from API data.
+
+    Args:
+        entity: The entity to get name for
+        device_info: Device info from the API
+        device_id_to_name: Mapping of device_id to device name for sub-devices
+
+    Returns:
+        The name to use for object_id computation
+    """
+    if entity.name:
+        # Named entity: use entity name
+        return entity.name
+    if entity.device_id != 0:
+        # Empty name on sub-device: use sub-device name
+        return device_id_to_name[entity.device_id]
+    if infer_name_add_mac_suffix(device_info) or device_info.friendly_name:
+        # Empty name on main device with MAC suffix or friendly_name: use friendly_name
+        # (even if empty - this is bug-for-bug compatibility for MAC suffix case)
+        return device_info.friendly_name
+    # Empty name on main device, no friendly_name: use device name
+    return device_info.name
+
+
+def compute_entity_object_id(
+    entity: EntityInfo,
+    device_info: DeviceInfo,
+    device_id_to_name: dict[int, str],
+) -> str:
+    """Compute expected object_id for an entity.
+
+    Args:
+        entity: The entity to compute object_id for
+        device_info: Device info from the API
+        device_id_to_name: Mapping of device_id to device name for sub-devices
+
+    Returns:
+        The computed object_id string
+    """
+    name_for_id = _get_name_for_object_id(entity, device_info, device_id_to_name)
+    return compute_object_id(name_for_id)
+
+
+def compute_entity_hash(
+    entity: EntityInfo,
+    device_info: DeviceInfo,
+    device_id_to_name: dict[int, str],
+) -> int:
+    """Compute expected object_id hash for an entity.
+
+    Args:
+        entity: The entity to compute hash for
+        device_info: Device info from the API
+        device_id_to_name: Mapping of device_id to device name for sub-devices
+
+    Returns:
+        The computed FNV-1 hash
+    """
+    name_for_id = _get_name_for_object_id(entity, device_info, device_id_to_name)
+    return fnv1_hash_object_id(name_for_id)
+
+
+def verify_entity_object_id(
+    entity: EntityInfo,
+    device_info: DeviceInfo,
+    device_id_to_name: dict[int, str],
+) -> None:
+    """Verify an entity's object_id and hash match the expected values.
+
+    Args:
+        entity: The entity to verify
+        device_info: Device info from the API
+        device_id_to_name: Mapping of device_id to device name for sub-devices
+
+    Raises:
+        AssertionError: If object_id or hash doesn't match expected value
+    """
+    expected_object_id = compute_entity_object_id(
+        entity, device_info, device_id_to_name
+    )
+    assert entity.object_id == expected_object_id, (
+        f"object_id mismatch for entity '{entity.name}': "
+        f"expected '{expected_object_id}', got '{entity.object_id}'"
+    )
+
+    expected_hash = compute_entity_hash(entity, device_info, device_id_to_name)
+    assert entity.key == expected_hash, (
+        f"hash mismatch for entity '{entity.name}': "
+        f"expected {expected_hash:#x}, got {entity.key:#x}"
+    )
+
+
+def verify_all_entities(
+    entities: list[EntityInfo],
+    device_info: DeviceInfo,
+) -> None:
+    """Verify all entities have correct object_id and hash values.
+
+    Args:
+        entities: List of entities to verify
+        device_info: Device info from the API
+
+    Raises:
+        AssertionError: If any entity's object_id or hash doesn't match
+    """
+    # Build device_id -> name lookup from sub-devices
+    device_id_to_name = {d.device_id: d.name for d in device_info.devices}
+
+    for entity in entities:
+        verify_entity_object_id(entity, device_info, device_id_to_name)

tests/integration/fixtures/fnv1_hash_object_id.yaml

@@ -0,0 +1,76 @@
+esphome:
+  name: fnv1-hash-object-id-test
+  platformio_options:
+    build_flags:
+      - "-DDEBUG"
+  on_boot:
+    - lambda: |-
+        using esphome::fnv1_hash_object_id;
+
+        // Test basic lowercase (hash matches Python fnv1_hash_object_id("foo"))
+        uint32_t hash_foo = fnv1_hash_object_id("foo", 3);
+        if (hash_foo == 0x408f5e13) {
+          ESP_LOGI("FNV1_OID", "foo PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "foo FAILED: 0x%08x != 0x408f5e13", hash_foo);
+        }
+
+        // Test uppercase conversion (should match lowercase)
+        uint32_t hash_Foo = fnv1_hash_object_id("Foo", 3);
+        if (hash_Foo == 0x408f5e13) {
+          ESP_LOGI("FNV1_OID", "upper PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "upper FAILED: 0x%08x != 0x408f5e13", hash_Foo);
+        }
+
+        // Test space to underscore conversion ("foo bar" -> "foo_bar")
+        uint32_t hash_space = fnv1_hash_object_id("foo bar", 7);
+        if (hash_space == 0x3ae35aa1) {
+          ESP_LOGI("FNV1_OID", "space PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "space FAILED: 0x%08x != 0x3ae35aa1", hash_space);
+        }
+
+        // Test underscore preserved ("foo_bar")
+        uint32_t hash_underscore = fnv1_hash_object_id("foo_bar", 7);
+        if (hash_underscore == 0x3ae35aa1) {
+          ESP_LOGI("FNV1_OID", "underscore PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "underscore FAILED: 0x%08x != 0x3ae35aa1", hash_underscore);
+        }
+
+        // Test hyphen preserved ("foo-bar")
+        uint32_t hash_hyphen = fnv1_hash_object_id("foo-bar", 7);
+        if (hash_hyphen == 0x438b12e3) {
+          ESP_LOGI("FNV1_OID", "hyphen PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "hyphen FAILED: 0x%08x != 0x438b12e3", hash_hyphen);
+        }
+
+        // Test special chars become underscore ("foo!bar" -> "foo_bar")
+        uint32_t hash_special = fnv1_hash_object_id("foo!bar", 7);
+        if (hash_special == 0x3ae35aa1) {
+          ESP_LOGI("FNV1_OID", "special PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "special FAILED: 0x%08x != 0x3ae35aa1", hash_special);
+        }
+
+        // Test complex name ("My Sensor Name" -> "my_sensor_name")
+        uint32_t hash_complex = fnv1_hash_object_id("My Sensor Name", 14);
+        if (hash_complex == 0x2760962a) {
+          ESP_LOGI("FNV1_OID", "complex PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "complex FAILED: 0x%08x != 0x2760962a", hash_complex);
+        }
+
+        // Test empty string returns FNV1_OFFSET_BASIS
+        uint32_t hash_empty = fnv1_hash_object_id("", 0);
+        if (hash_empty == 0x811c9dc5) {
+          ESP_LOGI("FNV1_OID", "empty PASSED");
+        } else {
+          ESP_LOGE("FNV1_OID", "empty FAILED: 0x%08x != 0x811c9dc5", hash_empty);
+        }
+
+host:
+api:
+logger:

tests/integration/fixtures/object_id_api_verification.yaml

@@ -0,0 +1,125 @@
+esphome:
+  name: object-id-test
+  friendly_name: Test Device
+  # Enable MAC suffix - host MAC is 98:35:69:ab:f6:79, suffix is "abf679"
+  # friendly_name becomes "Test Device abf679"
+  name_add_mac_suffix: true
+  # Sub-devices for testing empty-name entities on devices
+  devices:
+    - id: sub_device_1
+      name: Sub Device One
+    - id: sub_device_2
+      name: Sub Device Two
+
+host:
+
+api:
+
+logger:
+
+sensor:
+  # Test 1: Basic name -> object_id = "temperature_sensor"
+  - platform: template
+    name: "Temperature Sensor"
+    id: sensor_basic
+    lambda: return 42.0;
+    update_interval: 60s
+
+  # Test 2: Uppercase name -> object_id = "uppercase_name"
+  - platform: template
+    name: "UPPERCASE NAME"
+    id: sensor_uppercase
+    lambda: return 43.0;
+    update_interval: 60s
+
+  # Test 3: Special characters -> object_id = "special__chars_"
+  - platform: template
+    name: "Special!@Chars#"
+    id: sensor_special
+    lambda: return 44.0;
+    update_interval: 60s
+
+  # Test 4: Hyphen preserved -> object_id = "temp-sensor"
+  - platform: template
+    name: "Temp-Sensor"
+    id: sensor_hyphen
+    lambda: return 45.0;
+    update_interval: 60s
+
+  # Test 5: Underscore preserved -> object_id = "temp_sensor"
+  - platform: template
+    name: "Temp_Sensor"
+    id: sensor_underscore
+    lambda: return 46.0;
+    update_interval: 60s
+
+  # Test 6: Mixed case with spaces -> object_id = "living_room_temperature"
+  - platform: template
+    name: "Living Room Temperature"
+    id: sensor_mixed
+    lambda: return 47.0;
+    update_interval: 60s
+
+  # Test 7: Empty name - uses friendly_name with MAC suffix
+  # friendly_name = "Test Device abf679" -> object_id = "test_device_abf679"
+  - platform: template
+    name: ""
+    id: sensor_empty_name
+    lambda: return 48.0;
+    update_interval: 60s
+
+binary_sensor:
+  # Test 8: Different platform same conversion rules
+  - platform: template
+    name: "Door Open"
+    id: binary_door
+    lambda: return true;
+
+  # Test 9: Numbers in name -> object_id = "sensor_123"
+  - platform: template
+    name: "Sensor 123"
+    id: binary_numbers
+    lambda: return false;
+
+switch:
+  # Test 10: Long name with multiple spaces
+  - platform: template
+    name: "My Very Long Switch Name Here"
+    id: switch_long
+    lambda: return false;
+    turn_on_action:
+      - logger.log: "on"
+    turn_off_action:
+      - logger.log: "off"
+
+text_sensor:
+  # Test 11: Name starting with number (should work fine)
+  - platform: template
+    name: "123 Start"
+    id: text_num_start
+    lambda: return {"test"};
+    update_interval: 60s
+
+button:
+  # Test 12: Named entity on sub-device -> object_id from entity name
+  - platform: template
+    name: "Device Button"
+    id: button_on_device
+    device_id: sub_device_1
+    on_press: []
+
+  # Test 13: Empty name on sub-device -> object_id from device name
+  # Device name "Sub Device One" -> object_id = "sub_device_one"
+  - platform: template
+    name: ""
+    id: button_empty_on_device1
+    device_id: sub_device_1
+    on_press: []
+
+  # Test 14: Empty name on different sub-device
+  # Device name "Sub Device Two" -> object_id = "sub_device_two"
+  - platform: template
+    name: ""
+    id: button_empty_on_device2
+    device_id: sub_device_2
+    on_press: []

tests/integration/fixtures/object_id_friendly_name_no_mac_suffix.yaml

@@ -0,0 +1,27 @@
+esphome:
+  name: test-device
+  # friendly_name set but NO MAC suffix
+  # Empty-name entity should use friendly_name for object_id
+  friendly_name: My Friendly Device
+
+host:
+
+api:
+
+logger:
+
+sensor:
+  # Empty name entity - should use friendly_name for object_id
+  # friendly_name = "My Friendly Device" -> object_id = "my_friendly_device"
+  - platform: template
+    name: ""
+    id: sensor_empty_name
+    lambda: return 42.0;
+    update_interval: 60s
+
+  # Named entity for comparison
+  - platform: template
+    name: "Temperature"
+    id: sensor_named
+    lambda: return 43.0;
+    update_interval: 60s

tests/integration/fixtures/object_id_no_friendly_name_no_mac_suffix.yaml

@@ -0,0 +1,25 @@
+esphome:
+  name: test-device
+  # No friendly_name set, no MAC suffix
+  # OLD behavior: object_id = device name because Python pre-computed with fallback
+
+host:
+
+api:
+
+logger:
+
+sensor:
+  # Empty name entity - OLD behavior used device name as fallback
+  - platform: template
+    name: ""
+    id: sensor_empty_name
+    lambda: return 42.0;
+    update_interval: 60s
+
+  # Named entity for comparison
+  - platform: template
+    name: "Temperature"
+    id: sensor_named
+    lambda: return 43.0;
+    update_interval: 60s

tests/integration/fixtures/object_id_no_friendly_name_with_mac_suffix.yaml

@@ -0,0 +1,26 @@
+esphome:
+  name: test-device
+  # No friendly_name set, MAC suffix enabled
+  # OLD behavior: object_id = "" (empty) because is_object_id_dynamic_() used App.get_friendly_name() directly
+  name_add_mac_suffix: true
+
+host:
+
+api:
+
+logger:
+
+sensor:
+  # Empty name entity - OLD behavior produced empty object_id when MAC suffix enabled
+  - platform: template
+    name: ""
+    id: sensor_empty_name
+    lambda: return 42.0;
+    update_interval: 60s
+
+  # Named entity for comparison
+  - platform: template
+    name: "Temperature"
+    id: sensor_named
+    lambda: return 43.0;
+    update_interval: 60s

tests/integration/test_fnv1_hash_object_id.py

@@ -0,0 +1,75 @@
+"""Integration test for fnv1_hash_object_id function.
+
+This test verifies that the C++ fnv1_hash_object_id() function in
+esphome/core/helpers.h produces the same hash values as the Python
+fnv1_hash_object_id() function in esphome/helpers.py.
+
+If this test fails, one of the implementations has diverged and needs
+to be updated to match the other.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import re
+
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_fnv1_hash_object_id(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test that C++ fnv1_hash_object_id matches Python implementation."""
+
+    test_results: dict[str, str] = {}
+    all_tests_complete = asyncio.Event()
+    expected_tests = {
+        "foo",
+        "upper",
+        "space",
+        "underscore",
+        "hyphen",
+        "special",
+        "complex",
+        "empty",
+    }
+
+    def on_log_line(line: str) -> None:
+        """Capture log lines with test results."""
+        # Strip ANSI escape codes
+        clean_line = re.sub(r"\x1b\[[0-9;]*m", "", line)
+        # Look for our test result messages
+        # Format: "[timestamp][level][FNV1_OID:line]: test_name PASSED"
+        match = re.search(r"\[FNV1_OID:\d+\]:\s+(\w+)\s+(PASSED|FAILED)", clean_line)
+        if match:
+            test_name = match.group(1)
+            result = match.group(2)
+            test_results[test_name] = result
+            if set(test_results.keys()) >= expected_tests:
+                all_tests_complete.set()
+
+    async with (
+        run_compiled(yaml_config, line_callback=on_log_line),
+        api_client_connected() as client,
+    ):
+        device_info = await client.device_info()
+        assert device_info is not None
+        assert device_info.name == "fnv1-hash-object-id-test"
+
+        # Wait for all tests to complete or timeout
+        try:
+            await asyncio.wait_for(all_tests_complete.wait(), timeout=2.0)
+        except TimeoutError:
+            pytest.fail(f"Tests timed out. Got results for: {set(test_results.keys())}")
+
+        # Verify all tests passed
+        for test_name in expected_tests:
+            assert test_name in test_results, f"{test_name} test not found"
+            assert test_results[test_name] == "PASSED", (
+                f"{test_name} test failed - C++ and Python hash mismatch"
+            )

tests/integration/test_object_id_api_verification.py

@@ -0,0 +1,176 @@
+"""Integration test to verify object_id from API matches Python computation.
+
+This test verifies a three-way match between:
+1. C++ object_id generation (get_object_id_to using to_sanitized_char/to_snake_case_char)
+2. C++ hash generation (fnv1_hash_object_id in helpers.h)
+3. Python computation (sanitize/snake_case in helpers.py, fnv1_hash_object_id)
+
+The API response contains C++ computed values, so verifying API == Python
+implicitly verifies C++ == Python == API for both object_id and hash.
+
+This is important for the planned migration to remove object_id from the API
+protocol and have clients (like aioesphomeapi) compute it from the name.
+See: https://github.com/esphome/backlog/issues/76
+
+Test cases covered:
+- Named entities with various characters (uppercase, special chars, hyphens, etc.)
+- Empty-name entities on main device (uses device's friendly_name with MAC suffix)
+- Empty-name entities on sub-devices (uses sub-device's name)
+- Named entities on sub-devices (uses entity name, not device name)
+- MAC suffix handling (name_add_mac_suffix modifies friendly_name at runtime)
+- Both object_id string and hash (key) verification
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from esphome.helpers import fnv1_hash_object_id
+
+from .entity_utils import compute_object_id, verify_all_entities
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+# Host platform default MAC: 98:35:69:ab:f6:79 -> suffix "abf679"
+MAC_SUFFIX = "abf679"
+
+
+# Expected entities with their own names and expected object_ids
+# Format: (entity_name, expected_object_id)
+NAMED_ENTITIES = [
+    # sensor platform
+    ("Temperature Sensor", "temperature_sensor"),
+    ("UPPERCASE NAME", "uppercase_name"),
+    ("Special!@Chars#", "special__chars_"),
+    ("Temp-Sensor", "temp-sensor"),
+    ("Temp_Sensor", "temp_sensor"),
+    ("Living Room Temperature", "living_room_temperature"),
+    # binary_sensor platform
+    ("Door Open", "door_open"),
+    ("Sensor 123", "sensor_123"),
+    # switch platform
+    ("My Very Long Switch Name Here", "my_very_long_switch_name_here"),
+    # text_sensor platform
+    ("123 Start", "123_start"),
+    # button platform - named entity on sub-device (uses entity name, not device name)
+    ("Device Button", "device_button"),
+]
+
+# Sub-device names and their expected object_ids for empty-name entities
+# Format: (device_name, expected_object_id)
+SUB_DEVICE_EMPTY_NAME_ENTITIES = [
+    ("Sub Device One", "sub_device_one"),
+    ("Sub Device Two", "sub_device_two"),
+]
+
+
+@pytest.mark.asyncio
+async def test_object_id_api_verification(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test that object_id from API matches Python computation.
+
+    Tests:
+    1. Named entities - object_id computed from entity name
+    2. Empty-name entities - object_id computed from friendly_name (with MAC suffix)
+    3. Hash verification - key can be computed from name
+    4. Generic verification - all entities can have object_id computed from API data
+    """
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        # Get device info
+        device_info = await client.device_info()
+        assert device_info is not None
+
+        # Device name should include MAC suffix (hyphen separator)
+        assert device_info.name == f"object-id-test-{MAC_SUFFIX}", (
+            f"Device name mismatch: got '{device_info.name}'"
+        )
+        # Friendly name should include MAC suffix (space separator)
+        expected_friendly_name = f"Test Device {MAC_SUFFIX}"
+        assert device_info.friendly_name == expected_friendly_name, (
+            f"Friendly name mismatch: got '{device_info.friendly_name}'"
+        )
+
+        # Get all entities
+        entities, _ = await client.list_entities_services()
+
+        # Create a map of entity names to entity info
+        entity_map = {}
+        for entity in entities:
+            entity_map[entity.name] = entity
+
+        # === Test 1: Verify each named entity ===
+        for entity_name, expected_object_id in NAMED_ENTITIES:
+            assert entity_name in entity_map, (
+                f"Entity '{entity_name}' not found in API response. "
+                f"Available: {list(entity_map.keys())}"
+            )
+
+            entity = entity_map[entity_name]
+
+            # Verify object_id matches expected
+            assert entity.object_id == expected_object_id, (
+                f"Entity '{entity_name}': object_id mismatch. "
+                f"API returned '{entity.object_id}', expected '{expected_object_id}'"
+            )
+
+            # Verify Python computation matches
+            computed = compute_object_id(entity_name)
+            assert computed == expected_object_id, (
+                f"Entity '{entity_name}': Python computation mismatch. "
+                f"Computed '{computed}', expected '{expected_object_id}'"
+            )
+
+            # Verify hash can be computed from the name
+            hash_from_name = fnv1_hash_object_id(entity_name)
+            assert hash_from_name == entity.key, (
+                f"Entity '{entity_name}': hash mismatch. "
+                f"Python hash {hash_from_name:#x}, API key {entity.key:#x}"
+            )
+
+        # === Test 2: Verify empty-name entities ===
+        # Empty-name entities have name="" in API, object_id comes from:
+        # - Main device: friendly_name (with MAC suffix)
+        # - Sub-device: device name
+
+        # Get all empty-name entities
+        empty_name_entities = [e for e in entities if e.name == ""]
+        # We expect 3: 1 on main device, 2 on sub-devices
+        assert len(empty_name_entities) == 3, (
+            f"Expected 3 empty-name entities, got {len(empty_name_entities)}"
+        )
+
+        # Build device_id -> device_name map from device_info
+        device_id_to_name = {d.device_id: d.name for d in device_info.devices}
+
+        # Verify each empty-name entity
+        for entity in empty_name_entities:
+            if entity.device_id == 0:
+                # Main device - uses friendly_name with MAC suffix
+                expected_name = expected_friendly_name
+            else:
+                # Sub-device - uses device name
+                assert entity.device_id in device_id_to_name, (
+                    f"Entity device_id {entity.device_id} not found in devices"
+                )
+                expected_name = device_id_to_name[entity.device_id]
+
+            expected_object_id = compute_object_id(expected_name)
+            assert entity.object_id == expected_object_id, (
+                f"Empty-name entity (device_id={entity.device_id}): object_id mismatch. "
+                f"API: '{entity.object_id}', expected: '{expected_object_id}' "
+                f"(from name '{expected_name}')"
+            )
+
+            # Verify hash matches
+            expected_hash = fnv1_hash_object_id(expected_name)
+            assert entity.key == expected_hash, (
+                f"Empty-name entity (device_id={entity.device_id}): hash mismatch. "
+                f"API key: {entity.key:#x}, expected: {expected_hash:#x}"
+            )
+
+        # === Test 3: Verify ALL entities using the algorithm from entity_utils ===
+        # This uses the algorithm that aioesphomeapi will use to compute object_id
+        # client-side from API data.
+        verify_all_entities(entities, device_info)

tests/integration/test_object_id_friendly_name_no_mac_suffix.py

@@ -0,0 +1,81 @@
+"""Integration test for object_id with friendly_name but no MAC suffix.
+
+This test covers Branch 4 of the algorithm:
+- Empty name on main device
+- NO MAC suffix enabled
+- friendly_name IS set
+- Result: use friendly_name for object_id
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from esphome.helpers import fnv1_hash_object_id
+
+from .entity_utils import (
+    compute_object_id,
+    infer_name_add_mac_suffix,
+    verify_all_entities,
+)
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_object_id_friendly_name_no_mac_suffix(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test object_id when friendly_name is set but no MAC suffix.
+
+    This covers Branch 4 of the algorithm:
+    - Empty name entity
+    - name_add_mac_suffix = false (or not set)
+    - friendly_name = "My Friendly Device"
+    - Expected: object_id = "my_friendly_device"
+    """
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        device_info = await client.device_info()
+        assert device_info is not None
+
+        # Device name should NOT include MAC suffix
+        assert device_info.name == "test-device"
+
+        # Friendly name should be set
+        assert device_info.friendly_name == "My Friendly Device"
+
+        entities, _ = await client.list_entities_services()
+
+        # Find the empty-name entity
+        empty_name_entities = [e for e in entities if e.name == ""]
+        assert len(empty_name_entities) == 1
+
+        entity = empty_name_entities[0]
+
+        # Should use friendly_name for object_id (Branch 4)
+        expected_object_id = compute_object_id("My Friendly Device")
+        assert expected_object_id == "my_friendly_device"  # Verify our expectation
+        assert entity.object_id == expected_object_id, (
+            f"Expected object_id '{expected_object_id}' from friendly_name, "
+            f"got '{entity.object_id}'"
+        )
+
+        # Hash should match friendly_name
+        expected_hash = fnv1_hash_object_id("My Friendly Device")
+        assert entity.key == expected_hash, (
+            f"Expected hash {expected_hash:#x}, got {entity.key:#x}"
+        )
+
+        # Named entity should work normally
+        named_entities = [e for e in entities if e.name == "Temperature"]
+        assert len(named_entities) == 1
+        assert named_entities[0].object_id == "temperature"
+
+        # Verify our inference: no MAC suffix in this test
+        assert not infer_name_add_mac_suffix(device_info), (
+            "Device name should NOT have MAC suffix"
+        )
+
+        # Verify the full algorithm from entity_utils works for ALL entities
+        verify_all_entities(entities, device_info)

tests/integration/test_object_id_no_friendly_name.py

@@ -0,0 +1,140 @@
+"""Integration tests for object_id when friendly_name is not set.
+
+These tests verify bug-for-bug compatibility with the old behavior:
+
+1. With MAC suffix enabled + no friendly_name:
+   - OLD: is_object_id_dynamic_() was true, used App.get_friendly_name() directly
+   - OLD: object_id = "" (empty) because friendly_name was empty
+   - NEW: Must maintain same behavior for compatibility
+
+2. Without MAC suffix + no friendly_name:
+   - OLD: is_object_id_dynamic_() was false, used pre-computed object_id_c_str_
+   - OLD: Python computed object_id with fallback to device name
+   - NEW: Must maintain same behavior (object_id = device name)
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from esphome.helpers import fnv1_hash_object_id
+
+from .entity_utils import compute_object_id, verify_all_entities
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+# Host platform default MAC: 98:35:69:ab:f6:79 -> suffix "abf679"
+MAC_SUFFIX = "abf679"
+
+# FNV1 offset basis - hash of empty string
+FNV1_OFFSET_BASIS = 2166136261
+
+
+@pytest.mark.asyncio
+async def test_object_id_no_friendly_name_with_mac_suffix(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test object_id when friendly_name not set but MAC suffix enabled.
+
+    OLD behavior (bug-for-bug compatibility):
+    - is_object_id_dynamic_() returned true (no own name AND mac suffix enabled)
+    - format_dynamic_object_id() used App.get_friendly_name() directly
+    - Since friendly_name was empty, object_id was empty
+
+    This was arguably a bug, but we maintain it for compatibility.
+    """
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        device_info = await client.device_info()
+        assert device_info is not None
+
+        # Device name should include MAC suffix
+        expected_device_name = f"test-device-{MAC_SUFFIX}"
+        assert device_info.name == expected_device_name
+
+        # Friendly name should be empty (not set in config)
+        assert device_info.friendly_name == ""
+
+        entities, _ = await client.list_entities_services()
+
+        # Find the empty-name entity
+        empty_name_entities = [e for e in entities if e.name == ""]
+        assert len(empty_name_entities) == 1
+
+        entity = empty_name_entities[0]
+
+        # OLD behavior: object_id was empty because App.get_friendly_name() was empty
+        # This is bug-for-bug compatibility
+        assert entity.object_id == "", (
+            f"Expected empty object_id for bug-for-bug compatibility, "
+            f"got '{entity.object_id}'"
+        )
+
+        # Hash should be FNV1_OFFSET_BASIS (hash of empty string)
+        assert entity.key == FNV1_OFFSET_BASIS, (
+            f"Expected hash of empty string ({FNV1_OFFSET_BASIS:#x}), "
+            f"got {entity.key:#x}"
+        )
+
+        # Named entity should work normally
+        named_entities = [e for e in entities if e.name == "Temperature"]
+        assert len(named_entities) == 1
+        assert named_entities[0].object_id == "temperature"
+
+        # Verify the full algorithm from entity_utils works for ALL entities
+        verify_all_entities(entities, device_info)
+
+
+@pytest.mark.asyncio
+async def test_object_id_no_friendly_name_no_mac_suffix(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test object_id when friendly_name not set and no MAC suffix.
+
+    OLD behavior:
+    - is_object_id_dynamic_() returned false (mac suffix not enabled)
+    - Used object_id_c_str_ which was pre-computed in Python
+    - Python used get_base_entity_object_id() with fallback to CORE.name
+
+    Result: object_id = sanitize(snake_case(device_name))
+    """
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        device_info = await client.device_info()
+        assert device_info is not None
+
+        # Device name should NOT include MAC suffix
+        assert device_info.name == "test-device"
+
+        # Friendly name should be empty (not set in config)
+        assert device_info.friendly_name == ""
+
+        entities, _ = await client.list_entities_services()
+
+        # Find the empty-name entity
+        empty_name_entities = [e for e in entities if e.name == ""]
+        assert len(empty_name_entities) == 1
+
+        entity = empty_name_entities[0]
+
+        # OLD behavior: object_id was computed from device name
+        expected_object_id = compute_object_id("test-device")
+        assert entity.object_id == expected_object_id, (
+            f"Expected object_id '{expected_object_id}' from device name, "
+            f"got '{entity.object_id}'"
+        )
+
+        # Hash should match device name
+        expected_hash = fnv1_hash_object_id("test-device")
+        assert entity.key == expected_hash, (
+            f"Expected hash {expected_hash:#x}, got {entity.key:#x}"
+        )
+
+        # Named entity should work normally
+        named_entities = [e for e in entities if e.name == "Temperature"]
+        assert len(named_entities) == 1
+        assert named_entities[0].object_id == "temperature"
+
+        # Verify the full algorithm from entity_utils works for ALL entities
+        verify_all_entities(entities, device_info)

tests/unit_tests/core/test_entity_helpers.py

@@ -27,13 +27,9 @@ from esphome.helpers import sanitize, snake_case
 
 from .common import load_config_from_fixture
 
-# Pre-compiled regex patterns for extracting object IDs from expressions
-# Matches both old format: .set_object_id("obj_id")
-# and new format: .set_name_and_object_id("name", "obj_id")
-OBJECT_ID_PATTERN = re.compile(r'\.set_object_id\(["\'](.*?)["\']\)')
-COMBINED_PATTERN = re.compile(
-    r'\.set_name_and_object_id\(["\'].*?["\']\s*,\s*["\'](.*?)["\']\)'
-)
+# Pre-compiled regex pattern for extracting names from set_name calls
+# Matches: .set_name("name", hash) or .set_name("name")
+SET_NAME_PATTERN = re.compile(r'\.set_name\(["\']([^"\']*)["\']')
 
 FIXTURES_DIR = Path(__file__).parent.parent / "fixtures" / "core" / "entity_helpers"
 
@@ -276,14 +272,21 @@ def setup_test_environment() -> Generator[list[str], None, None]:
 
 
 def extract_object_id_from_expressions(expressions: list[str]) -> str | None:
-    """Extract the object ID that was set from the generated expressions."""
+    """Extract the object ID that would be computed from set_name calls.
+
+    Since object_id is now computed from the name (via snake_case + sanitize),
+    we extract the name from set_name() calls and compute the expected object_id.
+    For empty names, we fall back to CORE.friendly_name or CORE.name.
+    """
     for expr in expressions:
-        # First try new combined format: .set_name_and_object_id("name", "obj_id")
-        if match := COMBINED_PATTERN.search(expr):
-            return match.group(1)
-        # Fall back to old format: .set_object_id("obj_id")
-        if match := OBJECT_ID_PATTERN.search(expr):
-            return match.group(1)
+        if match := SET_NAME_PATTERN.search(expr):
+            name = match.group(1)
+            if name:
+                return sanitize(snake_case(name))
+            # Empty name - fall back to friendly_name or device name
+            if CORE.friendly_name:
+                return sanitize(snake_case(CORE.friendly_name))
+            return sanitize(snake_case(CORE.name)) if CORE.name else None
     return None
 
 
@@ -757,3 +760,140 @@ def test_entity_duplicate_validator_same_name_no_enhanced_message() -> None:
         r"Each entity on a device must have a unique name within its platform\.$",
     ):
         validator(config2)
+
+
+@pytest.mark.asyncio
+async def test_setup_entity_empty_name_with_device(
+    setup_test_environment: list[str],
+) -> None:
+    """Test setup_entity with empty entity name on a sub-device.
+
+    For empty-name entities, Python passes 0 and C++ calculates the hash
+    at runtime from the device's actual name.
+    """
+    added_expressions = setup_test_environment
+
+    # Mock get_variable to return a mock device
+    original_get_variable = entity_helpers.get_variable
+
+    async def mock_get_variable(id_: ID) -> MockObj:
+        return MockObj("sub_device_1")
+
+    entity_helpers.get_variable = mock_get_variable
+
+    var = MockObj("sensor1")
+    device_id = ID("sub_device_1", type="Device")
+
+    config = {
+        CONF_NAME: "",
+        CONF_DISABLED_BY_DEFAULT: False,
+        CONF_DEVICE_ID: device_id,
+    }
+
+    await setup_entity(var, config, "sensor")
+
+    entity_helpers.get_variable = original_get_variable
+
+    # Check that set_device was called
+    assert any("sensor1.set_device" in expr for expr in added_expressions)
+
+    # For empty-name entities, Python passes 0 - C++ calculates hash at runtime
+    assert any('set_name("", 0)' in expr for expr in added_expressions), (
+        f"Expected set_name with hash 0, got {added_expressions}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_setup_entity_empty_name_with_mac_suffix(
+    setup_test_environment: list[str],
+) -> None:
+    """Test setup_entity with empty name and MAC suffix enabled.
+
+    For empty-name entities, Python passes 0 and C++ calculates the hash
+    at runtime from friendly_name (bug-for-bug compatibility).
+    """
+    added_expressions = setup_test_environment
+
+    # Set up CORE.config with name_add_mac_suffix enabled
+    CORE.config = {"name_add_mac_suffix": True}
+    # Set friendly_name to a specific value
+    CORE.friendly_name = "My Device"
+
+    var = MockObj("sensor1")
+
+    config = {
+        CONF_NAME: "",
+        CONF_DISABLED_BY_DEFAULT: False,
+    }
+
+    await setup_entity(var, config, "sensor")
+
+    # For empty-name entities, Python passes 0 - C++ calculates hash at runtime
+    assert any('set_name("", 0)' in expr for expr in added_expressions), (
+        f"Expected set_name with hash 0, got {added_expressions}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_setup_entity_empty_name_with_mac_suffix_no_friendly_name(
+    setup_test_environment: list[str],
+) -> None:
+    """Test setup_entity with empty name, MAC suffix enabled, but no friendly_name.
+
+    For empty-name entities, Python passes 0 and C++ calculates the hash
+    at runtime. In this case C++ will hash the empty friendly_name
+    (bug-for-bug compatibility).
+    """
+    added_expressions = setup_test_environment
+
+    # Set up CORE.config with name_add_mac_suffix enabled
+    CORE.config = {"name_add_mac_suffix": True}
+    # Set friendly_name to empty
+    CORE.friendly_name = ""
+
+    var = MockObj("sensor1")
+
+    config = {
+        CONF_NAME: "",
+        CONF_DISABLED_BY_DEFAULT: False,
+    }
+
+    await setup_entity(var, config, "sensor")
+
+    # For empty-name entities, Python passes 0 - C++ calculates hash at runtime
+    assert any('set_name("", 0)' in expr for expr in added_expressions), (
+        f"Expected set_name with hash 0, got {added_expressions}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_setup_entity_empty_name_no_mac_suffix_no_friendly_name(
+    setup_test_environment: list[str],
+) -> None:
+    """Test setup_entity with empty name, no MAC suffix, and no friendly_name.
+
+    For empty-name entities, Python passes 0 and C++ calculates the hash
+    at runtime from the device name.
+    """
+    added_expressions = setup_test_environment
+
+    # No MAC suffix (either not set or False)
+    CORE.config = {}
+    # No friendly_name
+    CORE.friendly_name = ""
+    # Device name is set
+    CORE.name = "my-test-device"
+
+    var = MockObj("sensor1")
+
+    config = {
+        CONF_NAME: "",
+        CONF_DISABLED_BY_DEFAULT: False,
+    }
+
+    await setup_entity(var, config, "sensor")
+
+    # For empty-name entities, Python passes 0 - C++ calculates hash at runtime
+    assert any('set_name("", 0)' in expr for expr in added_expressions), (
+        f"Expected set_name with hash 0, got {added_expressions}"
+    )

tests/unit_tests/test_helpers.py

@@ -279,6 +279,77 @@ def test_sanitize(text, expected):
     assert actual == expected
 
 
+@pytest.mark.parametrize(
+    ("name", "expected_hash"),
+    (
+        # Basic strings - hash of sanitize(snake_case(name))
+        ("foo", 0x408F5E13),
+        ("Foo", 0x408F5E13),  # Same as "foo" (lowercase)
+        ("FOO", 0x408F5E13),  # Same as "foo" (lowercase)
+        # Spaces become underscores
+        ("foo bar", 0x3AE35AA1),  # Transforms to "foo_bar"
+        ("Foo Bar", 0x3AE35AA1),  # Same (lowercase + underscore)
+        # Already snake_case
+        ("foo_bar", 0x3AE35AA1),
+        # Special chars become underscores
+        ("foo!bar", 0x3AE35AA1),  # Transforms to "foo_bar"
+        ("foo@bar", 0x3AE35AA1),  # Transforms to "foo_bar"
+        # Hyphens are preserved
+        ("foo-bar", 0x438B12E3),
+        # Numbers are preserved
+        ("foo123", 0xF3B0067D),
+        # Empty string
+        ("", 0x811C9DC5),  # FNV1_OFFSET_BASIS (no chars processed)
+        # Single char
+        ("a", 0x050C5D7E),
+        # Mixed case and spaces
+        ("My Sensor Name", 0x2760962A),  # Transforms to "my_sensor_name"
+    ),
+)
+def test_fnv1_hash_object_id(name, expected_hash):
+    """Test fnv1_hash_object_id produces expected hashes.
+
+    These expected values were computed to match the C++ implementation
+    in esphome/core/helpers.h. If this test fails after modifying either
+    implementation, ensure both Python and C++ versions stay in sync.
+    """
+    actual = helpers.fnv1_hash_object_id(name)
+
+    assert actual == expected_hash
+
+
+def _fnv1_hash_py(s: str) -> int:
+    """Python implementation of FNV-1 hash for verification."""
+    hash_val = 2166136261  # FNV1_OFFSET_BASIS
+    for c in s:
+        hash_val = (hash_val * 16777619) & 0xFFFFFFFF  # FNV1_PRIME
+        hash_val ^= ord(c)
+    return hash_val
+
+
+@pytest.mark.parametrize(
+    "name",
+    (
+        "Simple",
+        "With Space",
+        "MixedCase",
+        "special!@#chars",
+        "already_snake_case",
+        "123numbers",
+    ),
+)
+def test_fnv1_hash_object_id_matches_manual_calculation(name):
+    """Verify fnv1_hash_object_id matches snake_case + sanitize + standard FNV-1."""
+    # Manual calculation: snake_case -> sanitize -> fnv1_hash
+    transformed = helpers.sanitize(helpers.snake_case(name))
+    expected = _fnv1_hash_py(transformed)
+
+    # Direct calculation via fnv1_hash_object_id
+    actual = helpers.fnv1_hash_object_id(name)
+
+    assert actual == expected
+
+
 @pytest.mark.parametrize(
     "text, expected",
     ((["127.0.0.1", "fe80::1", "2001::2"], ["2001::2", "127.0.0.1", "fe80::1"]),),