Protocol v21 is live on the testnet with the release of v1.18.0-beta. This is a prerelease, so don’t expect mainnet stability yet. Key changes include congestion tracking improvements, faster sync for validators, and breaking updates to the Rust SDK.

Protocol v21 Features

• Congestion limit overshoot: The shared-object congestion tracker now allows overshoots of up to 100 on the testnet. This also applies to the gas price feedback mechanism and transactions using randomness. (PR #10313)
• Fast commit syncer: Devnet nodes can use the consensus_fast_commit_sync flag to enable a faster commit syncer. This improves the catch-up rate for committed SubDAGs to ~20x-30x compared to the previous ~4x-6x. (PR #9585)
• AuthContext native functions: Added getters for AuthContext, which might simplify certain operations. (PR #10431)

Node Updates (Validators and Full Nodes)

• RestIndexStore in snapshots: Database snapshots now include the RestIndexStore. (PR #10380)
• Fast commit syncer toggle: The enable_fast_commit_syncer parameter (default false) lets nodes activate the fast commit syncer when the protocol flag is enabled. This improves recovery from large commit gaps. (PR #9585)
• Traffic sketch fixes: Bugs in test_traffic_sketch_with_slow_blocks are resolved, and the test is re-enabled. (PR #10420)

CLI Enhancements

• Network-specific builds: iota move build now supports the --client.env flag, letting you build packages with network-specific address values. (PR #10261)
• Conflict checks: Fixed an issue where conflicting addresses weren’t properly checked during compilation. (PR #10226)

Rust SDK Breaking Changes

• MoveAuthenticator updates: The MoveAuthenticator type now supports versioning and must be constructed as V1. This breaks compatibility with previous versions, so update your implementations accordingly. (PR #10431)

Why It Matters

For devs running testnet validators, the fast commit syncer is a big deal. Faster recovery from commit gaps—up to 30x faster—is a significant improvement for maintaining network stability during high-load periods. The congestion overshoot changes are also testnet-only for now, so if you’re testing gas price feedback mechanisms or randomness-based transactions, you’ll want to pay attention.

The Rust SDK breaking change means you’ll need to refactor any code using MoveAuthenticator. If you’re building or maintaining tools with the SDK, check your dependencies and update to v1.18.0-beta to avoid compatibility issues.

For CLI users, the new --client.env flag is helpful if you’re working across multiple networks. You can now build packages with the correct address values for each environment, which should streamline testing and deployment workflows.

What’s Next

Since this is a beta release, mainnet isn’t affected yet. Testnet users should report any issues on GitHub to help stabilize the release. Full details and the complete changelog are here.

Sources: v1.18.0-beta, v1.18.0-alpha, v1.17.2