CryptoSlate
Polygon Labs ordered node operators running pre-hardfork binaries to upgrade immediately, after its Aug 27 security review confirmed that Bor nodes below v2.10.0 and Heimdall nodes below v0.11.0 are no longer following canonical consensus. Austin activated at mainnet block 91,949,700 on the execution-client side, while Kyoto activated at height 51,533,000 on Aug 18 at 10:10:31 UTC for the consensus layer.
Why it matters
Austin closed two resource-exhaustion paths in Bor. The first capped the gas Bor consumes while processing state-sync events from L1-to-L2 bridge deposits, since those calls previously executed outside the block's gas ceiling and could stall processing if enough events landed. The second removed Bor's TxDependency extra-data field after researchers showed a producer could stuff an oversized blob into the field and crash peer nodes handling a sibling block. Polygon said it has not observed mainnet disruption from Austin and framed the changes as proactive fixes.
Kyoto's highest-severity fix added a byte-level nesting check on google.protobuf.Any messages in Heimdall, closing a vector where a single cheap transaction could force every validator to spend heavily on decoding. Kyoto also capped fee-coin lists before an O(n) validation scan (Heimdall permits one fee coin), normalized checkpoint signature recovery bytes so a valid signature cannot fail recovery on Ethereum, made repeated producer-downtime messages idempotent, bound milestone-range votes to the signed parent hash, prevented failed future-span creations from blocking milestone commitment, and made replay keys for topup, clerk, and stake events injective across out-of-range log indexes. A previously reported hour-long RPC disruption was tied to a Heimdall hotfix in this same code path.
Market impact
Both hardforks are plain binary upgrades with no state migration or genesis change, so nodes that upgraded on schedule have nothing to do. Operators already past the relevant height on an older client must install the applicable release, roll back to a pre-hardfork block if needed, and resync under Polygon's guidance.
Frequently asked questions
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What do node operators need to do after the Austin and Kyoto hardforks?
Operators running Bor below v2.10.0 or Heimdall below v0.11.0 must install the latest release, roll back to a pre-hardfork block if needed, and resync under Polygon's guidance. Nodes that already upgraded on schedule need no action.
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When did Austin and Kyoto activate on Polygon PoS mainnet?
Austin activated at block 91,949,700 on the execution-client side. Kyoto activated at height 51,533,000 on Aug 18 at 10:10:31 UTC for the consensus layer. Both activation heights have now passed.
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What did the Austin hardfork fix in Polygon PoS?
Austin capped the gas Bor consumes while processing state-sync events from L1-to-L2 bridge deposits and removed the TxDependency extra-data field, which had no size limit and could let a producer crash peer nodes with an oversized blob. Polygon classified both as resource-exhaustion risks.
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What was Kyoto's highest-severity fix?
Kyoto added a byte-level nesting check on google.protobuf.Any messages in Heimdall, closing a vector where a single cheap transaction could force every validator to spend heavily on decoding. A previously reported hour-long RPC disruption was tied to a hotfix in this same code path.
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Do these hardforks require a state migration or resync from scratch?
No. Both are plain binary upgrades with no state migration or genesis change. Nodes that had not diverged require no resync, though operators already past the relevant height on an older client must roll back and resync under Polygon guidance.
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