AVM has released FritzOS 8.40 as a new beta version for two additional cable routers. The FritzBox 6690 Cable and the FritzBox 6670 Cable can now be updated with the beta. The update prepares both models for the upcoming FritzOS 8.50 and also fixes three bugs related to Internet and Wi-Fi.
Key points at a glance:
- FritzOS 8.40 is now available as a lab beta for the FritzBox 6690 Cable and 6670 Cable.
- The firmware prepares the cable routers for FritzOS 8.50.
- Three minor bugs related to downstream display, interoperability, and repeater display have been fixed.
- Installation can be done via the user interface or manually using the lab file.
Two New Cable Routers in the FritzOS 8.40 Lab
Now that AVM has recently rolled out the stable FritzOS 8.25 to an increasing number of models, the lab cycle for the next generation continues. The current beta round has already included several DSL and fiber-optic models in recent days, including the FritzBox 7690, 7590 AX, and 5690 Pro. Now two cable routers are following suit. The following version has been available for download for them since July 29, 2026:
| Model | FritzOS Version | Date |
|---|---|---|
| FritzBox 6690 Cable | 8.40-134929 | July 29, 2026 |
| FritzBox 6670 Cable | 8.40-134930 | July 29, 2026 |
FritzOS 8.40 Fixes These Issues
Even though the firmware is being prepared for FritzOS 8.50 behind the scenes, the visible changes this time are relatively minor. AVM lists exactly three fixes:
- In some cases, the Online Monitor did not display values for the total downstream. This has now been fixed.
- Interoperability on certain ports is no longer restricted.
- Incorrect graphical displays on the main page in repeater mode are a thing of the past.
A Look Ahead to FritzOS 8.50
Even more exciting than the current bug fixes is what the Lab is working toward. With FritzOS 8.50, AVM is promising, among other things, new features for the MyFRITZ!App, an SOS call with up to four emergency contacts, and enhancements to Smart Home and parental controls. A Matter Bridge feature is also planned for the FritzBox 5690 Pro, which will bring additional smart home devices into the home network. If you want to try out the new features right now, the Lab is the place to be—but you’ll have to put up with the occasional beta glitch.
Install FritzOS 8.40 as a Lab Beta
If a beta is already running on the FritzBox, the router will automatically find the update via the user interface. If you’re switching from a stable version to the beta program, download the appropriate file from the FRITZ! Lab page and then install it under System > Update > FritzOS File.
Before making the switch, you should ensure that the latest stable FritzOS version is running and create a backup of your device settings. If problems arise, you can quickly restore the previous state using this backup.
Conclusion
For the FritzBox 6690 Cable and 6670 Cable, FritzOS 8.40 is primarily an intermediate step: three minor bug fixes and preparation for the significantly larger FritzOS 8.50. For tinkerers who want to test new features early, it’s worth taking the leap into the lab. Those who prefer to run their cable router in a stable environment can relax and wait for the final release.
Source: FRITZ! Lab
