Polygon: Upgrade Bor and Heimdall after Austin, Kyoto hard forks

Polygon Labs warned that any node on Polygon PoS running Bor or Heimdall binaries older than the August hard forks has diverged from the network’s canonical consensus and must upgrade to rejoin accepted history.

The Austin hard fork activated for Bor at mainnet block 91,949,700. Polygon released Bor v2.10.0 to implement Austin; later point releases such as v2.10.1 are also available. Austin caps gas charged for state-sync events originating from L1-to-L2 bridge deposits to prevent expensive state-syncs from delaying block processing. It also removes the TxDependency extra-data field from the wire format, closing a vector where an unbounded producer-supplied blob could crash peers.

The Kyoto hard fork activated for Heimdall at height 51,533,000, timestamped Aug. 18, 10:10:31 UTC in Polygon’s release notes. Heimdall v0.11.0 implements Kyoto. The release introduces a byte-level nesting check for google.protobuf.Any messages at mempool admission and block proposal processing to block deeply nested payloads that could force validators to spend excessive CPU decoding them. Kyoto also limits fee-coin entries before an O(n) validation scan and constrains integration logic to a single fee coin to avoid expensive fee-list validations.

Additional Heimdall changes normalize checkpoint signature recovery bytes so valid signatures cannot fail recovery on Ethereum, make repeated producer-downtime messages idempotent, bind milestone-range votes to the signed parent hash, and prevent a failed future-span creation from blocking milestone commitment. Replay keys for topup, clerk, and stake events were made injective for out-of-range log indexes to prevent distinct Layer-1 events from shadowing each other.

Polygon described both hard forks as plain binary upgrades with no state migration or genesis changes. Nodes that had not passed the activation heights before upgrading remain on the canonical chain and require no resynchronization. Operators who were already past the activation heights on older clients must install Bor v2.10.0 (or later) or Heimdall v0.11.0, roll back to a point before the hard fork if necessary, and resynchronize following Polygon’s guidance to follow the accepted history.

Polygon reported it has not observed any mainnet disruption tied to the upgrades and characterized the changes as proactive fixes for client resource-exhaustion and denial-of-service risks. The company emphasized operators should update promptly to avoid running nodes that no longer reflect the canonical Polygon PoS chain.