Simplicity SDK Version 2026.6.1 - Release Notes (Jul 29, 2026)#

The primary tool for the Silicon Labs IoT software development ecosystem, combining wireless software development kits (SDKs) and platform into a single, integrated package.

Release Announcements
Release Summary

Release Announcements#

LLVM Compiler Support Now Available#

The Simplicity SDK now supports the LLVM/Clang 21.1.1 compiler across all Series 2 and Series 3 devices, giving developers another powerful option for building high-performance, memory-efficient applications.

LLVM/Clang delivers improvements in code size and significant execution performance, with greater than 20% gains depending on their application and workload. Its advanced optimization capabilities and enhanced math libraries help developers maximize the performance of Silicon Labs MCUs while reducing flash memory requirements.

LLVM/Clang support is fully integrated into the Simplicity development environment and is available through both:

Simplicity Studio VS Code extension
CMake / Ninja CLI build system

Optimized for Series 3#

LLVM/Clang is particularly beneficial for Series 3 devices, including xG301, where its enhanced optimization pipeline and improved math libraries can help developers take full advantage of the architecture. Compute-intensive workloads (including AI/ML, DSP, sensor processing, and signal analysis) can benefit from improved execution efficiency while maintaining a smaller application footprint.

Flexible Optimization Options#

The Simplicity SDK supports both:

Standard LLVM/Clang compilation
LLVM/Clang with Link Time Optimization (LTO) for even greater whole-program optimization, enabling additional reductions in code size and further performance improvements.

By adding LLVM/Clang support, the Simplicity SDK gives developers greater flexibility to optimize their applications for performance, memory footprint, and power efficiency— helping accelerate development while maximizing the capabilities of Silicon Labs Series 2 and Series 3 devices.

LLVM support for Wi-Fi and 91x products is coming later this year.

Release Model#

Beginning with the 2026.6 release, Simplicity SDK releases follow a predictable biannual release model with two release types:

June Long-Term Support (LTS) release: The recommended baseline for production programs. During the 30-month standard maintenance window, an LTS release may receive maintenance patches and is eligible for technical support.
December Interim release: A shorter-maintained release for prototyping, early feature access, and development work that will move to a later LTS release. The December Interim release receives 6 months of standard maintenance and support.

Simplicity SDK releases prior to 2026.6 provide 18 months of maintenance and support.

Gecko SDK 4.5 LTS provides on-going support and maintenance for active Series 0 and 1 devices.

Customers who need to remain on a specific SDK release beyond the standard maintenance window may use Silicon Labs' SDK Extended Maintenance Service to extend maintenance for that release.

Simplicity SDK Packaging and Distribution#

Starting with the 2025.12 release, the Simplicity SDK transitions from GitHub-based monolithic delivery to a modular, Conan-based package model.

To obtain and work with the Simplicity SDK 2025.12, customers must use Silicon Labs Tool (SLT) v1.1.0 or newer, available through:

SLT-CLI (v1.1.0+) – a standalone command-line tool
Simplicity Installer (v1.1.0+) – a graphical installer that integrates SLT-CLI functionality

This update also introduces a new directory structure organized by technology and functional domain, which may affect how SDKs are integrated, consumed, and automated in developer workflows.

Developer Guidance#

CLI development (Headless or CI/CD dev setups)#

Need to update scripts that rely on ‘git clone’ and integrate SLT to manage and automate the SDK delivery.
Any tooling, scripts, or manual workflows that rely on fixed SDK paths may need to be updated accordingly.

GUI development (Simplicity Studio 6)#

No SLT-CLI integration is needed, but note that SDKs are now stored in versioned Conan package directories managed by SLT.
Directory path changes:
- Studio 5 (SDK 2025.6): ~/SimplicityStudio/SDKs/simplicity_sdk
- Studio 6 (SDK 2025.12): ~/.silabs/slt/installs/conan/p/simplxxxxxxxxxxx/p

Resources#

For SDK download and installation instructions, see the SLT-CLI Getting Started Guide or Simplicity Installer Getting Started Guide.
For project migration, refer to the SLC-CLI Project Migration Guide or Simplicity Studio Project Migration Guide.

Note: This Simplicity SDK release will be published on GitHub for reference purposes only, not recommended for development. Development should use the SDK packages delivered via SLT.

Release Summary#

Release Item	Version	Release Date	Key Features	Chip Enablement
Platform	6.1.1	Jul 29, 2026	Platform MCU Debug Logger: Logger support added (evaluation quality). Watchdog Manager: Watchdog manager support added (evaluation quality). sl_main: Added a new app_init_post_platform application hook in sl_main_second_stage_init, called after sl_platform_init, sl_driver_init, and sl_service_init complete and before sl_stack_init. This hook lets applications run initialization that depends on platform components, drivers, and services but must run before stacks are initialized. Linker: Added support for RAM-only execution for provisioning applications (GCC toolchain). Startup code: Added an assembly reset handler trampoline so safe code can execute before the C environment is loaded. Security None Bootloader None Micrium OS None CPC None MVP Math Library None	Platform MCU Added EFR32BG29/EFR32MG29 OPN and radio board support. Added EFR32FG2D and WPK Main Board (BRD4002B) support. Security None Bootloader None
RAIL Library	3.1.1	Jul 29, 2026	None	None
RAIL SDK	3.1.1	Jul 29, 2026	None	None
USB	1.7.1	Jul 29, 2026	None	None
Wi-Fi 6 + BLE (WiSeConnect)	4.1.1	Jul 29, 2026	Wi-Fi Multicast / broadcast filtering with IP allowlist and beacon-drop threshold WPA3 H2E SE BSS Max Idle Debug logging v2 (SL_DEBUG_LOG_V2) and Internal Buffer Manager Network Stack Added support to configure the DNS timeout from host. Added Embedded MQTT password length support up to 512 bytes. Added support for graceful TCP FIN handshake closure. Upgraded the lwIP stack from v2.1.2 to v2.2.1. SiWx91x Bluetooth LE Added support for dynamically enabling or disabling BLE. Added logging support for BLE. Added RC clock support for BLE. Added support for BLE stack bypass/offloading. Multiprotocol Support for concurrent two BLE connections with advertising extensions and WLAN TCP TX data transfer in NCP. Support for concurrent operation of eight BLE peripheral connections, two BLE central devices, and WLAN MQTT data transfer in NCP mode. SiWx91x Platform Added a Memory Manager Redirect component to redirect libc heap allocations to the CMSIS FreeRTOS heap_4 allocator by using heap wrappers. Upgraded GCC to 14.2 and enabled Link Time Optimization (LTO) for GCC-based builds. Updated SiWx91x platform code to Support BRD4002B Mainboard with EFR Driver Integration.	SoC: BRD4343C (SiW917Y-RB4343C) radio board for refreshed SiWG917Y SoC modules with external 32 kHz LP crystal pins; module OPNs SiWN917Y100LGAXA, SiWN917Y100LGNXA, SiWG917Y110LGNXA, SiWG917Y111MGNXA, SiWG917Y121MGNXA, SiWG917Y110LGAXA, SiWG917Y111MGAXA, SiWG917Y121MGAXA. NCP: BRD4357C (SiW917Y-RB4357C) radio board for refreshed SiWN917Y NCP modules with external 32 kHz LP crystal pins; module OPNs SiWN917Y100LGAXA, SiWN917Y100LGNXA. New boards: BRD4343C New chip components (SiWx917Y / SiWN917Y modules) under components/device/silabs/si91x/mcu/core/chip/component/: siwg917y110lgaxa, siwg917y110lgnxa siwg917y111mgaxa, siwg917y111mgnxa siwg917y121mgnxa, siwg917y121mgaxa siwn917y100lgaxa, siwn917y100lgnxa (NCP refresh)
OpenThread	3.1.1	Jul 29, 2026	None	None
Zigbee	9.1.1	Jul 29, 2026	None	None
Bluetooth LE	11.1.1	Jul 29, 2026	Example and Middleware Added Serial Port Profile middleware through the new spp component and related configuration and GATT service content. Added new Bluetooth peer manager and peer security middleware components for central, peripheral, filter, common, and security flows. Host Stack New flag `SL_BT_PERIODIC_ADVERTISER_INCLUDE_ADVERTISING_DATA_INFORMATION` in `sl_bt_periodic_advertiser_flags` enables the inclusion of Advertising Data Information (ADI) in transmitted periodic advertising PDUs. New command `sl_bt_periodic_advertiser_refresh_data_id` enables refreshing the Advertising Data ID (DID) without the need to provide the same data again. New mode `sl_bt_sync_report_non_duplicate` in `sl_bt_sync_reporting_mode_t` enables filtering duplicate periodic advertisements. The `bluetooth_feature_linklayer_interface` component provides new commands `sl_bt_linklayer_get_hci_connection_handle` and `sl_bt_linklayer_get_bgapi_connection_handle` for converting between link layer HCI connection handles and the BGAPI host stack connection handles. The application needs to convert between handle types when it uses the linklayer class to access low-level link layer functionality that uses connection handles. The bluetooth_feature_connection_analyzer feature can now maintain synchronization to the analyzed connection even if connection parameters or channel map is updated. The LLCP events need to be passed from the Central device to the connection analyzer device by the application. Use the `bluetooth_feature_connection_analyzer_llcp_report` component and the `sl_bt_linklayer_event_info_reporting_enable` command to enable the LLCP reporting on the Central. Pass the corresponding LLCP events from `sl_bt_evt_linklayer_event_info_report` events to the connection analyzer device and use `sl_bt_connection_analyzer_process_llcp_event` to process the event. New command `sl_bt_gap_set_privacy_mode_with_rpa_randomization` enables configuring local privacy with separate minimum and maximum RPA rotation intervals. When the interval bounds differ, advertiser and central-side RPAs are refreshed at randomized times within the configured range. Keeping the interval bounds equal preserves deterministic rotation behavior. New events `sl_bt_evt_gap_random_address_refresh` and `sl_bt_evt_advertiser_random_address_refresh` notify the application when the scanner/initiator or a stack-managed advertiser starts using a new private address. The related privacy mode commands document these events. New command `sl_bt_resolving_list_read_peer_resolvable_address` reads the current peer resolvable private address tracked by the controller for a device in the Resolving List. The `bluetooth_feature_cs` component adds Channel Sounding (CS) handover commands and events to the cs BGAPI class. Use the `bluetooth_feature_cs_handover_leader` and `bluetooth_feature_cs_handover_follower` components to enable the corresponding controller-side handover roles. Retrieve CS procedure parameters from the CS Leader, pass them to the CS Follower, and use the handover commands and events to synchronize the Follower to the CS procedure and LE connection and to control scheduled CS procedure execution. Controller Added support for ADI in Periodic Advertising and Periodic Advertising with Responses, improving interoperability with devices expecting this capability. Added Channel Map Update Indication support for the Periodic Advertising advertiser, enabling Adaptive Frequency Hopping with Periodic Advertising for improved reliability in congested or noisy RF environments. Multiprotocol CMP + BLE-RCP sample applications (Zigbee NCP + OpenThread RCP + Bluetooth RCP) Added new Concurrent Multiprotocol (CMP) co-processor sample projects that run Zigbee NCP, OpenThread RCP, and Bluetooth RCP on one EFR device. The Bluetooth side exposes a BLE controller over CPC so a Linux host can use the Silicon Labs RCP with CPCd and a standard Bluetooth stack (i.e. BlueZ). Zigbee and OpenThread host applications use the same CPC multiplexer model as existing NCP / RCP designs.	None.
Bluetooth Mesh	11.0.1	Jul 29, 2026	None	None
Bluetooth Location Services	11.1.1	Jul 29, 2026	Real-Time Locationing Service The RTL Service (`rtl_service`) is a new software component providing a unified API that works in both RTOS and bare-metal environments. The service automatically adapts: in RTOS mode it runs a dedicated processing task; in bare-metal mode it processes within the application main-loop. All API functions can be called from any task or interrupt context. The service handles mutual exclusion internally. Submit CS or Ranging Service (RAS) procedure data and receive distance estimates asynchronously through a result callback. RTL Library Version Function A function `sl_rtl_get_lib_version()` was added to return the exact library version. Algorithm Mode Enum Renaming The enum `sl_rtl_cs_algo_mode` field names have been renamed as follows: `SL_RTL_CS_ALGO_MODE_REAL_TIME_BASIC` renamed to `SL_RTL_CS_ALGO_MODE_TRACKING_ACCURACY_OPTIMIZED` `SL_RTL_CS_ALGO_MODE_REAL_TIME_FAST` renamed to `SL_RTL_CS_ALGO_MODE_TRACKING_LATENCY_OPTIMIZED` `SL_RTL_CS_ALGO_MODE_STATIC_HIGH_ACCURACY` renamed to `SL_RTL_CS_ALGO_MODE_STATIONARY`
Z-Wave	8.1.1	Jul 29, 2026	The Silicon Labs Bootloader now supports switching multiprotocol solutions. See the Creating Z-Wave-BLE SMP solution instruction for an example how to build a switched multiprotocol (SMP) firmware which combines a Z-Wave Switch On/Off application and a Bluetooth OTA DFU application that can upgrade the Z-Wave app Added an API to customize the DTPA noise margin from the application. Note: The noise margin is not stored in NVM. Applications must set the customized value after each initialization. Added component `zw_host_hibernation` to support hibernating host controller. Added component `zw_cc_wakeoncriticalmessage` to support alpha command class Wake On Critical Message. Supported new variant of Pro Kit Mainboard: BRD4002B. The new SHT40 sensor and the previous sensor are supported by a unidriver component for dynamic run-time selection in the sample applications. Note that it causes a RAM usage increase. To avoid increased RAM usage in production, use a dedicated driver for the sensors.	None
Wi-SUN	2.13.0	Jul 29, 2026	None	None
Silicon Labs Matter	2.9.1	Coming soon
Amazon Sidewalk	2.9.1	Jul 29, 2026	Cloud Light SoC Sample application. Supporting new Temperature sensor on WPK board. Application tab enablement in Sidewalk Assistant. Updated libraries to Amazon Stack 1.19.4. Stability improvements.	None
Connect	4.3.1	Jul 29, 2026	None	None
Machine Learning	3.0.1	Jul 29, 2026	New DX for adding ML Models to new or existing projects. New APIs to initialize, execute, and de-initialize ML models. Project upgrades require manual effort. See the AI-assisted migration prompt. Multiple-Model feature to add and execute multiple ML models in a project.	Added support for EFM32 devices.
Simplicity Connect Mobile App	3.3.1	Jul 29, 2026	Interoperability (IOP) Test Improvements	None

Note: Click here for earlier releases on GitHub.
Looking for older release notes? You can still access previous versions for both Simplicity SDK (prior to 2025.6.0) and Gecko SDK here.