Canton MainNet Moves to Canton 3.5 in Its First Logical Synchronizer Upgrade
CIP-0117 replaced upgrades that took 90 minutes to 3 hours of downtime with a switchover the Canton Network says completes in seconds or minutes, moving the network to protocol version 35.
The Canton Network said on 29 June 2026 that Logical Synchronizer Upgrades (LSUs) were live on MainNet with the release of Canton 3.5. The upgrade method lets the network's core infrastructure move to a new protocol version without the coordinated downtime and data migration that earlier upgrades required.
The approval
The change rests on CIP-0117, "Logical Synchronizers", by Wayne Collier, Moritz Kiefer and Rafael Guglielmetti. It was created on 28 April and approved on 5 June 2026.
- One logical ID. A stable logical synchronizer identity sits above the physical synchronizers that change with each upgrade, so validators keep one connection and their local history across protocol versions.
- The first LSU. The CIP scheduled the first upgrade from Canton protocol version 34 to version 35.
- Replacing the old procedure. It replaces the earlier synchronizer upgrades with downtime, used for Canton 3.1, 3.2 and 3.3 under CIP-0062 and for Canton 3.4 under CIP-0089.
Less downtime
According to the CIP, earlier upgrades meant 90 minutes to 3 hours of downtime and an export and import of migration dumps. With an LSU, it says, the switchover brings "seconds to minutes of noticeable downtime" and no migration dump. Topology changes, such as adding parties or nodes, pause for up to a few hours around the upgrade. The Canton blog says legacy synchronizers remain available for 30 days.
The schedule
The CIP and a Canton forum update of 12 June set the rollout, each step at 13:00 UTC with Splice 0.6.5 as the minimum validator version:
- DevNet: a practice upgrade on 3 June and the move to protocol version 35 on 10 June.
- TestNet: 17 June, after a topology freeze on 16 June.
- MainNet: 27 June, after a topology freeze on 26 June.
Super Validators could cancel an upgrade between the freeze and the upgrade time, and the CIP describes a roll-forward recovery for failures after it. The Canton blog post of 29 June did not give the exact time the MainNet switch completed.
What integrators need to know
From protocol version 35, the synchronizer ID field in externally signed prepared transactions holds the physical synchronizer ID, according to the CIP, which encourages integrators to use hashing scheme version 3. The CIP also says LSU development was funded in part by a grant from the Canton Development Fund.
Why it matters
Protocol upgrades on Canton used to mean hours of planned downtime across the whole network, which is hard to accept for institutions running settlement on it. Upgrades measured in seconds or minutes make it easier to ship protocol changes more often. The 12 June forum update already pointed to the next one: CantonBFT, a Canton-native ordering service prepared to replace CometBFT.
