ECIP 1088: Phoenix EVM and Protocol Upgrades Source

Author/raw PONG _GHMoaCXLT

Simple Summary

Enable the outstanding Ethereum Foundation Istanbul network protocol upgrades on the Ethereum Classic network in a hard-fork code-named Phoenix to enable maximum compatibility across these networks.


Add support for a subset of protocol-impacting changes introduced in the Ethereum Foundation (ETH) network via the Istanbul hardforks. The proposed changes for Ethereum Classic’s Phoenix upgrade include:

  • Add Blake2 compression function F precompile
  • Reduce alt_bn128 precompile gas costs
  • Add ChainID opcode
  • Repricing for trie-size-dependent opcodes
  • Calldata gas cost reduction
  • Rebalance net-metered SSTORE gas cost with consideration of SLOAD gas cost change

This document proposes the following blocks at which to implement these changes in the Classic networks:

  • 999_983 on Mordor Classic PoW-testnet (April, 2020)
  • 2_200_013 on Kotti Classic PoA-testnet (April, 2020)
  • 10_500_839 on Ethereum Classic PoW-mainnet (June, 2020)

For more information on the opcodes and their respective EIPs and implementations, please see the Specification section of this document.


To enhance the Ethereum Virtual Machine’s (EVM) capabilities, various opcodes shall be added to the Ethereum Classic networks, all of which have been in use on the Ethereum Foundation networks since end of 2019.


Technical specifications for each EIP can be found at those documents respectively:

  • EIP-152: Add Blake2 compression function F precompile
  • EIP-1108: Reduce alt_bn128 precompile gas costs
  • EIP-1344: Add ChainID opcode
  • EIP-1884: Repricing for trie-size-dependent opcodes
  • EIP-2028: Calldata gas cost reduction
  • EIP-2200: Rebalance net-metered SSTORE gas cost with consideration of SLOAD gas cost change


Interoperability: Establishing and maintaining interoperable behavior between Ethereum clients is essential for developers and end-user adoption, yielding benefits for all participating chains (e.g., ETH and ETC, Ropsten and Mordor, Görli and Kotti).

Immutability: None of the introduced new opcodes in the EVM has the potential to change the behavior of existing contracts; in the case where previously an arbitrary invalid bytecode would have been deployed to the network, none of them would be able to modify the state of the Ethereum Classic networks retrospectively. Adding opcodes to the EVM increases its functionality and should be considered a feature upgrade rather than a modification.


Adoption of the content of this ECIP requires a hard fork as it introduces changes that are not backward compatible.

The following clients with Ethereum Classic support implement the Istanbul features currently and will be able to support the Phoenix upgrade:

  • Core-Geth (maintained by ETC Core)
  • Hyperledger Besu (maintained by PegaSys and ChainSafe)

The following clients with Ethereum Classic support also implement Phoenix but let the users choose whether to adapt the upgrade or not.

  • Multi-Geth (maintained by the community)
  • OpenEthereum (previously Parity Ethereum, maintained by Gnosis)

Final Note

Both, the Geth Classic client and the Morden testnet will no longer be supported by the community and not recieve the Phoenix ugrades.

  • Users of the Geth Classic client are urged to migrate their services to Core-Geth or Hyperledger Besu. It is no longer recommended to run Geth Classic in production.
  • Users of the Morden Classic testnet are urged to migrate their applications to the Kotti Classic or Mordor Classic testnets.

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