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.
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.
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.
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.
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.
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.
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.
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.
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.
App.get_name() and App.get_friendly_name() now return const StringRef & instead of const std::string &. Most code compiles unchanged because StringRef provides .c_str(), .size(), .empty(), and implicit conversion to std::string. However, binding the result to const std::string & silently creates a heap-allocated temporary — update these references to const auto & to avoid the allocation.
This is a breaking change for external components in ESPHome 2026.3.0 and later.