ESPHome Developer Documentation

TemplatableFn: 4-Byte Templatable Storage for Trivially Copyable Types

J. Nick Koston — Sun, 19 Apr 2026 19:12:23 +0000

TemplatableFn: 4-Byte Templatable Storage for Trivially Copyable Types

The TEMPLATABLE_VALUE macro now uses TemplatableFn (4 bytes) instead of TemplatableValue (8 bytes) for trivially copyable types like float, uint32_t, bool, and enums. External components that call macro-generated setters with raw C++ constants instead of going through cg.templatable() will fail to compile.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

Climate and Fan Custom Mode Vectors Moved to Entity

J. Nick Koston — Sun, 19 Apr 2026 19:11:27 +0000

Climate and Fan Custom Mode Vectors Moved to Entity

Custom mode vectors (custom_fan_modes, custom_presets for climate; preset_modes for fan) are now stored on the entity base class instead of being rebuilt inside traits on every call. The old ClimateTraits and FanTraits setter methods are deprecated.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

wake_loop Moved from Socket Component into Core

J. Nick Koston — Thu, 09 Apr 2026 23:24:44 +0000

wake_loop Moved from Socket Component into Core

wake_loop_threadsafe() and related wake primitives have moved from the socket component into core. The require_wake_loop_threadsafe() opt-in is deprecated (now a no-op) — wake works unconditionally on all platforms.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

BLE Event Handler Dispatch Devirtualized

J. Nick Koston — Thu, 09 Apr 2026 23:19:12 +0000

BLE Event Handler Dispatch Devirtualized

Virtual handler interfaces (GAPEventHandler, GAPScanEventHandler, GATTcEventHandler, GATTsEventHandler, BLEStatusEventHandler) have been replaced with callback-based dispatch. External components that inherit from these interfaces must update their registration approach.

This is a developer breaking change for external components in ESPHome 2026.4.0 and later.

Modbus Helper Functions Moved to modbus::helpers

J. Nick Koston — Thu, 09 Apr 2026 23:17:23 +0000

Modbus Helper Functions Moved to modbus::helpers

Shared helper functions and types have been moved from modbus_controller to modbus::helpers to enable reuse by other modbus-based components. Deprecated shims keep the old names working until ESPHome 2026.10.0.

This is a developer breaking change for external components in ESPHome 2026.4.0 and later.

Trigger Trampolines Eliminated with build_callback_automation

J. Nick Koston — Thu, 09 Apr 2026 23:16:35 +0000

Trigger Trampolines Eliminated with build_callback_automation

Common entity trigger classes have been replaced with lightweight forwarder structs that fit inline in the callback system. The new build_callback_automation() API eliminates per-trigger object allocations. Several entity callback signatures have also changed to pass state as an argument.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

Sensor .raw_state Deprecated in Favor of get_raw_state()

J. Nick Koston — Thu, 09 Apr 2026 23:13:12 +0000

Sensor .raw_state Deprecated in Favor of get_raw_state()

Direct access to the sensor .raw_state member is now deprecated. Use get_raw_state() instead. The .raw_state member will be removed in ESPHome 2026.10.0.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

FlushResult Renamed to UARTFlushResult

J. Nick Koston — Thu, 09 Apr 2026 22:14:54 +0000

FlushResult Renamed to UARTFlushResult

The FlushResult enum introduced in ESPHome 2026.3.0 has been renamed to UARTFlushResult with prefixed enum values to follow ESPHome's naming conventions and avoid macro collisions.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

CallbackManager: std::function Replaced with Lightweight Callback

J. Nick Koston — Thu, 09 Apr 2026 22:08:33 +0000

CallbackManager: std::function Replaced with Lightweight Callback

CallbackManager and LazyCallbackManager now use a lightweight 8-byte Callback struct instead of std::function (16 bytes). External components that define their own callback registration methods using std::function should update to templates for optimal performance.

This is a breaking change for external components in ESPHome 2026.4.0 and later.

call_loop(), mark_failed(), and call_dump_config() Are No Longer Virtual

J. Nick Koston — Fri, 27 Mar 2026 18:18:45 +0000

call_loop(), mark_failed(), and call_dump_config() Are No Longer Virtual

Component::call_loop(), Component::mark_failed(), and Component::call_dump_config() are no longer virtual methods. External components that override any of these methods must remove them entirely and move logic to loop() or dump_config(). This saves 800+ bytes of flash globally from vtable elimination.