Old compatibility often holds infrastructure in place longer than it looks from the outside. The Tor Project has decided to cut that tie before a major network upgrade. The organization will end support for Tor 0.4.8 and earlier releases on September 1, 2026. The goal is to prepare the network for Arti, the new Tor implementation written in Rust.
What the Change Affects
The decision concerns the core Tor software. That software runs relays, onion services, and apps with built-in support for the anonymous network. The Tor Browser version number that most users see is not the main reference here. Current browser builds already use supported Tor versions. So users with an up-to-date Tor Browser should not run into problems.
Tor 0.4.8 reached end of life on June 1, 2026, and it no longer gets updates. Normally, the Tor Project tries not to break compatibility with old releases. In this case, however, support for the outdated branch blocks network changes and complicates work on Arti. You can read the project’s announcement for the full reasoning.
The Directory Protocol Change
The main technical change involves Tor’s directory protocol. Clients use it to receive data about relays and the state of the network. In Tor 0.4.9, two outdated fields were marked obsolete: TAP onion keys and family lines. Yet the network kept sending them for the sake of old versions.
Removing these fields brings a clear benefit. Clients will download less service data. That cuts bandwidth use and speeds up Tor startup, especially on slow connections. The problem is that Tor 0.4.8 and earlier still expect TAP onion keys in the directories. Once the fields disappear, the old software cannot process the network data correctly. As a result, it loses compatibility with Tor.
Why Arti Set the Hard Deadline
Arti is the second reason for the firm date. The Tor team finds it easier to connect a directory authority based on the new implementation when the code no longer has to support deprecated protocol elements. Dropping that legacy logic clears the path for the Rust relay work.
What Operators Should Do
The Tor Project is already contacting projects that may ship old Tor versions. It also asks the community to help find such packages and apps. Operators of relays, onion services, and software with embedded Tor should check their installed version. Then they should move to Tor 0.4.9 or newer before September 1, 2026. Without the update, those systems risk losing their connection to the network once the obsolete fields are removed from the directories.
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