Hardfork.isPostMerge

Check if hardfork is post-Merge (Proof of Stake consensus)

Try it Live

Run Hardfork examples in the interactive playground

The Merge

Active Since: Merge (September 15, 2022)

Aliases: “paris” (consensus layer name)

Consensus Change

Before Merge (Proof of Work):

• Miners compete to solve computational puzzles
• Block rewards: 2 ETH + transaction fees
• DIFFICULTY opcode returns mining difficulty

After Merge (Proof of Stake):

• Validators stake 32 ETH to propose blocks
• Block rewards: Transaction tips only (base fee burned)
• DIFFICULTY opcode returns beacon chain randomness (PREVRANDAO)

Changes Introduced

PREVRANDAO Opcode

Opcode: 0x44 (replaces DIFFICULTY)

Before Merge:

• Returns current block’s mining difficulty
• Used for difficulty-based calculations

After Merge:

• Returns beacon chain randomness (PREVRANDAO)
• Mix hash from beacon chain for randomness
• Breaking change: Contracts using DIFFICULTY for mining calculations will break

Block Production

Before Merge:

• Miners propose blocks via PoW
• Block time: ~13 seconds (variable)
• Uncle blocks possible

After Merge:

• Validators propose blocks via PoS
• Block time: 12 seconds (fixed)
• No uncle blocks

Economics

Before Merge:

• Block reward: 2 ETH per block
• Transaction fees to miners
• Issuance: ~4.3% annual

After Merge:

• Block reward: 0 ETH (only tips)
• Base fee burned (EIP-1559)
• Issuance: ~0.5% annual (90% reduction)

Usage Patterns

Consensus Detection

Determine consensus mechanism:

import { Hardfork } from 'tevm'

function getConsensusInfo(fork: BrandedHardfork) {
  if (fork.isPostMerge()) {
    return {
      consensus: "Proof of Stake",
      blockProducer: "validator",
      blockReward: "0 ETH (tips only)",
      difficultyOpcode: "PREVRANDAO",
      blockTime: "12s (fixed)"
    }
  }

  return {
    consensus: "Proof of Work",
    blockProducer: "miner",
    blockReward: "2 ETH + fees",
    difficultyOpcode: "DIFFICULTY",
    blockTime: "~13s (variable)"
  }
}

Mining Configuration

Validate mining configuration:

import { Hardfork } from 'tevm'

function validateMiningConfig(fork: BrandedHardfork, config: MiningConfig) {
  if (fork.isPostMerge() && config.mining) {
    throw new Error(
      "Mining not supported after Merge. " +
      "Ethereum uses Proof of Stake consensus."
    )
  }
}

Opcode Handling

Handle DIFFICULTY/PREVRANDAO opcode:

import { Hardfork } from 'tevm'

function handleDifficultyOpcode(fork: BrandedHardfork, value: bigint) {
  if (fork.isPostMerge()) {
    console.log("PREVRANDAO (beacon randomness):", value)
  } else {
    console.log("DIFFICULTY (mining difficulty):", value)
  }
}

Block Validation

Validate block structure:

import { Hardfork } from 'tevm'

function validateBlock(fork: BrandedHardfork, block: Block) {
  if (fork.isPostMerge()) {
    // PoS validation
    if (block.difficulty !== 0n) {
      throw new Error("PoS blocks must have difficulty = 0")
    }
    if (block.nonce !== 0n) {
      throw new Error("PoS blocks must have nonce = 0")
    }
    if (!block.mixHash) {
      throw new Error("PoS blocks require mixHash (PREVRANDAO)")
    }
  } else {
    // PoW validation
    if (block.difficulty === 0n) {
      throw new Error("PoW blocks must have non-zero difficulty")
    }
  }
}

Network Configuration

Check consensus mechanism:

import { Hardfork } from 'tevm'

function getNetworkType(fork: BrandedHardfork): string {
  return fork.isPostMerge() ? "mainnet-pos" : "mainnet-pow"
}

EIP References

Primary:

• EIP-3675 - Upgrade consensus to Proof of Stake
• EIP-4399 - Supplant DIFFICULTY opcode with PREVRANDAO

Impact

For Validators:

• Must stake 32 ETH to participate
• Earn tips + MEV (no base fee)
• Can be slashed for misbehavior

For Developers:

• DIFFICULTY opcode behavior changed
• Contracts using DIFFICULTY for mining logic will break
• Block time now consistent (12s)
• No more uncle blocks

For Network:

• 90% reduction in ETH issuance
• Consistent 12-second block times
• Finality from Casper FFG (2 epochs = ~13 minutes)
• 99.95% energy reduction

For Economics:

• Deflationary when base fee > issuance
• More predictable issuance schedule
• Staking yield replaces mining rewards

Breaking Changes

DIFFICULTY Opcode

Contracts using block.difficulty must update:

// Before Merge (PoW)
uint256 randomSeed = block.difficulty;  // Mining difficulty

// After Merge (PoS)
uint256 randomSeed = block.prevrandao;  // Beacon randomness
// Note: block.difficulty still works but returns prevrandao

Mining

All mining-related functionality removed:

• No block rewards for miners
• No mining difficulty adjustments
• No uncle blocks
• Mining software incompatible with PoS

See Also

• hasEIP1559 - Check EIP-1559 base fee availability (London)
• hasEIP4844 - Check blob transactions availability (Cancun)
• isAtLeast - General version comparison