Introduction

This documentation specifies changes of the PLCnext Control firmware regarding the firmware releases 2025.x, 2026.x and newer that may be relevant to user-generated applications which have been compiled with an SDK of firmware 2024.6 or before.

The major change is the non-compliance of the binary compatibility to former SDKs. Therefore, recompiling the user code that is based on any pre-2025 SDK is mandatory. Furthermore, some code adjustments might be necessary, which are mostly indicated through "deprecated" warnings. This documentation should be used together with the Change Notes for firmware releases 2025.x, 2026.x and newer regarding your PLC type.

The firmware releases 2025.x, 2026.x and newer come with some fundamentally updated parts of the underlying Linux® operating system and adapt the PLCnext Runtime System to those changes. This is intended to improve the long-term compatibility of binary files from C++ or MATLAB®/Simulink® programs, as well as components and apps.

The updates to the Linux® system will facilitate future updates to the kernel, the installation of new technologies and, above all, the security hardening of the system to be prepared for the Cyber Resilience Act in the European Union.

General advantages

The following optimizations are implemented and lay the foundations for later improvement:

• Increased stability due to adjustments of internal system functions
• Implementing long-term binary-compatible interfaces so we can continuously develop new RSC services
• Simplified implementation of user applications by means of standardized interfaces
• Several Linux® adaptations:
  • Increased security by splitting into separate processes and better use of Linux® capabilities
  • Removal of Linux® packages with high potential for security vulnerabilities
  • Switch to Linux® systemd for a better adaptation to new technology
  • Faster boot process due to parallel start of Linux® services
• New system monitoring for CPU, RAM, flash memory, and processes
• Implementation of interfaces to add WBM configuration pages for user components
• Support for versioning of user components
• Improved diagnostics by splitting into different log files
• Deep and secure integration of OCI containers for firmware functions and apps
• Newly designed Web-based Management 2:
  • single sign-on with OAuth2 allows for easy but secure access 
  • modern layout based on Angular.io that adapts to display sizes ("responsive")

Changes regarding application development

The substantial changes from developers' view are:

• The C++ standard is elevated to the more modern C++ 20 (formerly C++ 17) and standardized data types
• Library Arp.System.Core is substituted by the new library Arp.Base.Core
• The public classes of Arp.System.Acf were moved to the new library Arp.Base.Acf.Commons
• Refactoring of Logging substruction
• Removed RTLD_GLOBAL flag while loading shared libraries
• Update of several external libraries, e.g.:
  • CppFormat upgrade to libfmt 10.2.1
  • boost update to version 1.84 (but see boost version for details) 

Update recommendation

We recommend updating to latest the long-term supported firmware release (as of now: 2026.0 LTS) as part of your regular maintenance or update cycles. This ensures that you continuously benefit from the latest advancements and improvements of our platform. 

Please note that our update recommendation is part of our standard lifecycle and product strategy and does not constitute an assessment of specific applications or operational conditions. For project-specific requirements or individual evaluations, we will gladly support you. Thank you for your cooperation and your continued trust in our products.

The 2024.0 LTS release that is based on the established foundation of PLCnext Technology has received security-related fixes for an extended period. This allows customers to adapt their applications to the future firmware foundation according to their own schedules and still benefit from security fixes and patches. But there won't be a long-term supported firmware successor on the former code base.

Firmware releases 2025.x for PLCnext Control AXC F 2152 and AXC F 1152 have already been removed from the download sections of the Phoenix Contact product pages. This was necessary because of an issue of the new firmware foundation with 32-bit devices. For productive operation, customers who already adapted their applications to the future firmware foundation should update their PLCnext Control AXC F 2152 or AXC F 1152 devices to firmware release 2026.0 LTS as soon as possible.

Migration guidance

For updating from firmware releases 2024.6 or earlier to firmware releases 2025.x, 2026.x and newer, follow these steps:

• Back up your projects, licenses and configuration data.
• Check the current firmware release on your device:
  • Running firmware 2019.0 LTS up to 2021.9, update to the 2022.0 LTS release first.
  • Running firmware 2022.0 LTS up to 2024.6, update to the 2026.0.5 LTS release.
    ↪ On rebooting after a successful update, a script converts the network configuration.
• Reset your controller via shell command sudo plcnext-recover 4sudo recover-plcnext 4 (sorry for that glitch!).
  ↪ On rebooting the device starts up clean.

Now you can set up your device with the updated firmware:

• Enter the Web-based Management 2 and set up your configurations (Date and Time, active/inactive system services and so on).
• Review your applications, adapt and recompile C++ programs.
  Note: Depending on active services, the RAM usage and CPU load may be higher than before.
• If you're using PLCnext Technology Apps, check the PLCnext Store for versions compatible with firmware releases 2025.x, 2026.x and newer:  Due to the changes regarding C++ code, many of the PLCnext Technology apps need to be adapted and recompiled, too.
• Download your applications to your controller and validate their functionality.

Find all details for adapting your applications in the following Changes chapters.