top of page


Updated: Jun 8, 2023

Authors: Mikhail Kalinin, Danny Ryan


Mikhail Kalinin, Danny Ryan, "EIP-4399: Supplant DIFFICULTY opcode with PREVRANDAO," Ethereum Improvement Proposals, no. 4399, October 2021. [Online serial]. Available:

EIP-4399 Supplants the return value of the existing difficulty (0x44) opcode & renames it to PREVRANDAO (0X44)

At point of transition block of POS Upgrade, the Difficulty of the block must be = 0. Thereafter because POW is deprecated and there is no POW seal on the block. This means that the difficulty 0x44 instruction no longer has its previous semantic meaning.

EIP-4399 introduces backwards incompatibility changes to execution & validator of EVM state transition. This EIP utilizes the transition block & is tightly coupled with POS Upgrade introduced in EIP-3675. Thus, this EIP-4399 must be scheduled at the same time as EIP-3675.

Changes proposed by this EIP allow for smart contracts to determine whether the upgrade to POS has already happened. This can be tested by analyzing the return value of difficulty instruction.

3 views0 comments

Recent Posts

See All


Rated 0 out of 5 stars.
No ratings yet

Add a rating
bottom of page