PIP-51: Protocol Upgrade Mechanism
Explain how Pactus performs protocol upgrades.
| Authors | Pactus Development Team [[email protected]] |
|---|---|
| Discussion | View Discussion PIP-51 |
| Category | Core |
| Created | 2026-05-08 |
Table of Contents
Abstract #
This informational PIP describes the Pactus protocol upgrade mechanism. A protocol upgrade is similar to a hard fork in Proof-of-Work blockchains: it introduces backward-incompatible changes by raising the block version.
Nodes announce supported protocol versions during peer handshakes and block proposals so validators can detect when more than 75% of the committee’s total power supports the upgrade and safely activate the new block version.
Motivation #
Protocol upgrades are a necessary part of blockchain evolution. In Pactus, they must be handled in a way that minimizes disruption while ensuring that incompatible changes only become active when enough of the validating network has signaled support. This PIP explains how the upgrade process is signaled, decided, and activated.
Specification #
Protocol Upgrade Definition #
A protocol upgrade in Pactus is a backward-incompatible change that requires nodes to run newer software. The activation of such an upgrade is signaled by increasing the block version.
When the block version is increased, old nodes are no longer able to parse the new blocks because they do not support the new block version. As a result, old nodes cannot propose new blocks, and their proposals will be rejected by the network.
Version Announcement Channels #
Nodes announce their supported protocol version through two mechanisms.
Handshake Phase #
During the initial handshake between two directly connected peers, each node advertises the latest protocol version it supports.
Proposal Messages #
Whenever a proposer broadcasts a new block proposal, the proposal message also carries the proposer’s latest supported protocol version.
Network Version Snapshot #
Each validator maintains a view of the network by recording supported protocol versions from peers and proposals. This snapshot reflects the distributed support level for the latest protocol version among the validator set.
Activation Threshold #
A protocol upgrade is activated when a proposer detects that more than 75% of the committee’s total power supports the latest protocol version. Support is determined by the sum of the stake (power) of committee validators whose announced protocol version is greater than or equal to the target version, divided by the total committee power.
Once this threshold is satisfied, the proposer increases the block version and begins proposing blocks under the new version to other committee validators. Because more than 75% of the committee’s total power now supports the new block version, those blocks are expected to be validated successfully. Committee members that have not upgraded will not be able to commit the new blocks and will gradually be replaced by upgraded validators through the sortition process.
Post-Activation Behavior #
After the upgrade is activated, nodes that have not upgraded their software will no longer be able to parse or validate new blocks produced under the new version. These outdated nodes must upgrade to the latest software version in order to rejoin the network and synchronize the chain.
Copyright
Copyright and related rights waived via CC0.