fix(fork): use difficulty as prevrandao on more chains - #16456
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Polygon, Avalanche and Arbitrum keep the `difficulty` header field in use and return it from the `PREVRANDAO` opcode. Foundry took `prevrandao` from `mixHash`, which is zero on Polygon and Avalanche and carries packed L1 metadata on Arbitrum, so `block.prevrandao` diverged from the chain in forks and replays. BSC already had this treatment; the other chains now share it. Verified against live nodes: `PREVRANDAO` returns 1 on Polygon, Polygon Amoy, Avalanche, Avalanche Fuji, Arbitrum One, Nova and Sepolia, and Foundry now returns the same. Ethereum, Optimism and Base are unchanged.
mattsse
requested review from
0xrusowsky,
DaniPopes,
figtracer,
grandizzy,
mablr and
stevencartavia
as code owners
August 29, 2026 01:09
Contributor
✅ Changelog foundThe deterministic check will validate the changed entry. |
stevencartavia
approved these changes
Aug 29, 2026
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Polygon, Avalanche and Arbitrum keep the
difficultyheader field in use and return it from thePREVRANDAOopcode, the same way BSC does. Foundry derivesprevrandaofrommixHash, which is zero on Polygon and Avalanche and carries packed L1 metadata on Arbitrum, so a contract readingblock.prevrandaosaw0or a chunk of Arbitrum L1 header data instead of what the chain returns. BSC already had this handled by #9942; the other chains now share the same treatment, and the Arbitrum arm picks it up alongside the existingl1BlockNumberremap.Measured with a
PREVRANDAOprobe deployed through aneth_callstate override, comparing the node's answer against local execution at the same pinned block:10110110x00000000000286310000…1222Nothing else in the survey diverged: Gnosis, Linea, Scroll, Sonic, Celo, Mantle, Berachain and Cronos already matched.
This PR was written by Claude Code, including the survey behind it and this description. Verified against live nodes for every chain in the table.