Connect Version 4.2.0 - Release Notes (Jan 22, 2026)#

Simplicity SDK Version 2025.12.0

The Connect SDK is a complete software development suite for proprietary wireless applications that was previously part of the Proprietary SDK. Starting with the Connect SDK 4.0.0 release, Proprietary SDK is split into RAIL SDK and Connect SDK.

Connect SDK uses Silicon Labs Connect, an IEEE 802.15.4-based networking stack designed for customizable broad-based proprietary wireless networking solutions that require low power consumption and operate in either the sub-GHz or 2.4 GHz frequency bands. The solution is targeted towards simple network topologies.

Connect SDK is supplied with extensive documentation and sample applications. All examples are provided in source code within the Connect SDK sample applications.

Release Summary#

Key Features | API Changes | Bug Fixes | Chip Enablement

Key Features#

  • Memory Manager Integration: Stack now uses sl_memory_manager throughout for consistent memory handling.

  • RAIL 3.0.0. integration in both Stack and SDK.

API Changes#

None.

Bug Fixes#

Fixed memory leak when sending MAC messages fails using emberMacMessageSend.

Chip Enablement#

None.

Key Features#

New Features | Enhancements | Removed Features | Deprecated Features

New Features#

None.

Enhancements#

RAIL 3.0.0. usage: Stack and SDK are using the new and improved RAIL Library.

Removed Features#

None.

Deprecated Features#

None.

API Changes#

New APIs | Modified APIs | Removed APIs | Deprecated APIs

New APIs#

None.

Modified APIs#

None.

Removed APIs#

None.

Deprecated APIs#

None.

Bug Fixes#

ID Issue Description GitHub / Salesforce Reference (if any) Affected Software Variants, Hardware, Modes, Host Interfaces
1522109 Fixed a memory leak in emberMacMessageSend, which could occur when sending MAC messages failed due to error conditions, such as when the API was called while not connected to a network or with an invalid message length. Over time, this could have resulted in gradual memory depletion. None
  • Connect Stack
  • All supported boards
  • SoC, NCP mode

Chip Enablement#

None.

Application Example Changes#

New Examples | Modified Examples | Removed Examples | Deprecated Examples

New Examples#

None.

Modified Examples#

Example Name Changes Supported Software Variants if applicable Supported Modes Supported OPNs / Boards / OPN Combinations Supported Host Interfaces
All sample applications Updated include from em_chip.h to em_system.h. Standard
  • SoC
  • NCP
 All supported boards All
Connect - NCP sample application Updated memory allocation to use sl_memory_manager. Standard NCP All supported boards SPI, EUART, UART

Removed Examples#

None.

Deprecated Examples#

None.

Known Issues and Limitations#

ID Issue or Limitation Description GitHub / Salesforce Reference (if any) Workaround (if any) Affected Software Variants, Hardware, Modes, Host Interfaces
652925 EFR32XG21 is not supported for “Flex (Connect) - SoC Light Example DMP” and “Flex (Connect) - SoC Switch Example” None. None.
  • EFR32XG21
  • BRD4176A, BRD4179B, BRD4180A, BRD4180B, BRD4181A, BRD4181B, BRD4181C, BRD4195A, BRD4195B, BRD4196A, BRD4196B, BRD4332A
  • SoC
1139850 DMP instabilities with EFR32XG27 None. None.
  • EFR32XG27
  • BRD2602A, BRD4109A, BRD4110A, BRD4110B, BRD4111A, BRD4111B, BRD4113A, BRD4194A
  • SoC
501561 In the Legacy HAL component, the PA configuration is hardcoded regardless of the user or boards settings. None. Until this is changed to properly pull from the configuration header, the file ember-phy.c in the user's project will need to be modified by hand to reflect the desired PA mode, voltage, and ramp time.
  • All
  • All
  • SoC
None. When running the RAIL Multiprotocol Library (used, for example, when running DMP Connect+BLE), IR Calibration is not performed because of a known issue in the RAIL Multiprotocol Library. As result, there is an RX sensitivity loss in the order of 3 or 4 dBm. None.
  • All
  • All
  • SoC
None. Updating the Baremetal sample applications to RTOS causes build errors. None.

Follow the Platforms guide sl_main Baremetal to RTOS Application Transition
  • Connect SDK Baremetal sample applications
  • All supported boards
  • SoC, NCP mode
  • UART,SPI interface

Impact of Release Changes#

Impact Statements | Migration Guide

Impact Statements#

None.

Migration Guide#

Click here for the migration guide for deprecated, removed, and modified items.

Using This Release#

What's in the Release? | Compatible Software | Installation and Use | Help and Feedback

What's in the Release?#

Connect SDK 4.2.0 showcasing the usage of the Connect stack 4.2.0 with the latest Simplicity SDK.

Compatible Software#

None.

Installation and Use#

To upgrade your existing software with this release, see instructions here.

To run your first demo, see our Getting Started Guides.

To kick start your development, see our Developer's Guide.

To learn more about the software in this release, dive into our online documentation.

For information about Secure Vault Integration, see here.

To review Security and Software Advisory notifications and manage your notification preferences:

  1. Go to https://community.silabs.com/.

  2. Log in with your account credentials.

  3. Click your profile icon in the upper-right corner of the page.

  4. Select Notifications from the dropdown menu.

  5. In the Notifications section, go to the My Product Notifications tab to review historical Security and Software Advisory notifications

  6. To manage your preferences, use the Manage Notifications tab to customize which product updates and advisories you receive.

Help and Feedback#

SDK Release and Maintenance Policy#

See our SDK Release and Maintenance Policy.