FRITZ!OS 8.21 – Summary FRITZ!OS 8.21 is a stability‑focused update that FRITZ! (AVM) has rolled out across several of its newer FRITZ!Box models. The release improves performance, tightens security, and fixes a wide range...

[UK Sentinel]

FRITZ!OS 8.21 is a stability‑focused update that FRITZ! (AVM) has rolled out across several of its newer FRITZ!Box models. The release improves performance, tightens security, and fixes a wide range of issues reported since the introduction of FRITZ!OS 8.0. While not a feature‑heavy update, it delivers meaningful refinements across networking, telephony, Wi‑Fi, and smart home functions.

FRITZ! has been releasing 8.21 in waves, with the most recent rollout landing on 31 January 2026 for the latest hardware generation.

Key Improvements in FRITZ!OS 8.21

System & Stability

• General system stability improvements across all supported models
• Fixes for rare crashes and memory‑handling issues
• Improved responsiveness of the web interface

Internet & Networking

• Better IPv6 reliability and compatibility
• Enhanced VPN stability (IPSec & WireGuard)
• Improved handling of multi‑gigabit WAN connections on supported models

Wi‑Fi

• Optimised Wi‑Fi 6/6E performance
• Better roaming behaviour in mesh setups
• Fixes for occasional throughput drops under heavy load

Mesh Networking

• More reliable node synchronisation
• Improved handover between mesh repeaters
• Better detection of DFS radar events

Telephony

• SIP provider compatibility updates
• Improved DECT handset stability
• Fixes for call‑routing edge cases

Smart Home

• More reliable DECT ULE device pairing
• Improved energy‑monitoring accuracy
• Better handling of automation rules

Security

• Multiple security hardening improvements
• Updated internal components and libraries
• Strengthened protection against malformed network packet

https://fritz.com/en/pages/fritz-os

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