diff --git a/.gitignore b/.gitignore
index 3490453..cc91919 100644
--- a/.gitignore
+++ b/.gitignore
@@ -36,3 +36,4 @@ devnet/saved-cannon-data
 devnet/init.log
 devnet/l1-geth/
 profiling/
+devnet/mainnet.genesis.json
\ No newline at end of file
diff --git a/devnet/3-op-init.sh b/devnet/3-op-init.sh
index d83868e..a9113d6 100755
--- a/devnet/3-op-init.sh
+++ b/devnet/3-op-init.sh
@@ -12,22 +12,31 @@ sed_inplace() {
   fi
 }
 
-# Check if FORK_BLOCK is set
-if [ -z "$FORK_BLOCK" ]; then
-    echo " ❌ FORK_BLOCK environment variable is not set"
-    echo "Please set FORK_BLOCK in your .env file"
-    exit 1
-fi
+# ========================================
+# Genesis Preparation
+# ========================================
+if [ "$USE_FAKE_MAINNET" = "true" ]; then
+    # Fake mainnet mode: use unified script with mainnet genesis
+    source scripts/prepare-genesis.sh
+    _prepare_mainnet_genesis
+else
+    # Original generated genesis logic
+    if [ -z "$FORK_BLOCK" ]; then
+        echo " ❌ FORK_BLOCK environment variable is not set"
+        echo "Please set FORK_BLOCK in your .env file"
+        exit 1
+    fi
 
-FORK_BLOCK_HEX=$(printf "0x%x" "$FORK_BLOCK")
-sed_inplace '/"config": {/,/}/ s/"optimism": {/"legacyXLayerBlock": '"$((FORK_BLOCK + 1))"',\n    "optimism": {/' ./config-op/genesis.json
-sed_inplace 's/"parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000"/"parentHash": "'"$PARENT_HASH"'"/' ./config-op/genesis.json
-sed_inplace '/"70997970c51812dc3a010c7d01b50e0d17dc79c8": {/,/}/ s/"balance": "[^"]*"/"balance": "0x446c3b15f9926687d2c40534fdb564000000000000"/' ./config-op/genesis.json
-NEXT_BLOCK_NUMBER=$((FORK_BLOCK + 1))
-NEXT_BLOCK_NUMBER_HEX=$(printf "0x%x" "$NEXT_BLOCK_NUMBER")
-sed_inplace 's/"number": 0/"number": '"$NEXT_BLOCK_NUMBER"'/' ./config-op/rollup.json
-cp ./config-op/genesis.json ./config-op/genesis-reth.json
-sed_inplace 's/"number": "0x0"/"number": "'"$NEXT_BLOCK_NUMBER_HEX"'"/' ./config-op/genesis-reth.json
+    FORK_BLOCK_HEX=$(printf "0x%x" "$FORK_BLOCK")
+    sed_inplace '/"config": {/,/}/ s/"optimism": {/"legacyXLayerBlock": '"$((FORK_BLOCK + 1))"',\n    "optimism": {/' ./config-op/genesis.json
+    sed_inplace 's/"parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000"/"parentHash": "'"$PARENT_HASH"'"/' ./config-op/genesis.json
+    sed_inplace '/"70997970c51812dc3a010c7d01b50e0d17dc79c8": {/,/}/ s/"balance": "[^"]*"/"balance": "0x446c3b15f9926687d2c40534fdb564000000000000"/' ./config-op/genesis.json
+    NEXT_BLOCK_NUMBER=$((FORK_BLOCK + 1))
+    NEXT_BLOCK_NUMBER_HEX=$(printf "0x%x" "$NEXT_BLOCK_NUMBER")
+    sed_inplace 's/"number": 0/"number": '"$NEXT_BLOCK_NUMBER"'/' ./config-op/rollup.json
+    cp ./config-op/genesis.json ./config-op/genesis-reth.json
+    sed_inplace 's/"number": "0x0"/"number": "'"$NEXT_BLOCK_NUMBER_HEX"'"/' ./config-op/genesis-reth.json
+fi
 
 # Extract contract addresses from state.json and update .env file
 echo "🔧 Extracting contract addresses from state.json..."
diff --git a/devnet/example.env b/devnet/example.env
index ce39fe7..0033125 100644
--- a/devnet/example.env
+++ b/devnet/example.env
@@ -49,6 +49,11 @@ SKIP_BUILD_PRESTATE=false
 # Set to false if you need full mode with op-proposer, op-challenger, op-dispute-mon
 MIN_RUN=true
 
+# ==============================================================================
+# Fake Mainnet Configuration
+# ==============================================================================
+USE_FAKE_MAINNET=false
+
 # ==============================================================================
 # Docker & Network Configuration
 # ==============================================================================
diff --git a/devnet/scripts/prepare-genesis.sh b/devnet/scripts/prepare-genesis.sh
new file mode 100755
index 0000000..e6c034f
--- /dev/null
+++ b/devnet/scripts/prepare-genesis.sh
@@ -0,0 +1,233 @@
+#!/bin/bash
+# ==============================================================================
+# prepare-genesis.sh - Unified genesis preparation script
+# ==============================================================================
+# Supports two modes:
+#   1. Mainnet genesis mode (USE_FAKE_MAINNET=true)
+#      - Downloads and uses real mainnet genesis data (6.6GB+)
+#      - Requires MIN_RUN=true
+#   2. Generated genesis mode (default)
+#      - Uses genesis generated by op-deployer
+#
+# Usage:
+#   source scripts/prepare-genesis.sh   # Called from 3-op-init.sh
+#   ./scripts/prepare-genesis.sh        # Standalone execution
+# ==============================================================================
+
+set -e
+
+MAINNET_GENESIS_URL="https://okg-pub-hk.oss-cn-hongkong.aliyuncs.com/cdn/chain/xlayer/snapshot/merged.genesis.json.mainnet.tar.gz"
+MAINNET_GENESIS_PATH="mainnet.genesis.json"
+TEST_ACCOUNT_ADDRESS="0x70997970C51812dc3A010C7d01b50e0d17dc79C8"
+TEST_ACCOUNT_BALANCE="0x52B7D2DCC80CD2E4000000" # 100,000 ETH
+
+# ==============================================================================
+# Helper Functions
+# ==============================================================================
+_sed_inplace() {
+    if [[ "$OSTYPE" == "darwin"* ]]; then
+        sed -i '' "$@"
+    else
+        sed -i "$@"
+    fi
+}
+
+# ==============================================================================
+# Download Mainnet Genesis
+# ==============================================================================
+_download_mainnet_genesis() {
+    if [ -f "$MAINNET_GENESIS_PATH" ]; then
+        echo "✅ Mainnet genesis already exists: $MAINNET_GENESIS_PATH"
+        return 0
+    fi
+    
+    echo "📥 Downloading mainnet genesis..."
+    echo "   URL: $MAINNET_GENESIS_URL"
+    
+    local TAR_FILE="mainnet-genesis.tar.gz"
+    
+    # Download
+    if ! curl -L --progress-bar "$MAINNET_GENESIS_URL" -o "$TAR_FILE"; then
+        echo "❌ ERROR: Failed to download mainnet genesis"
+        exit 1
+    fi
+    
+    echo "📂 Extracting..."
+    tar -xzf "$TAR_FILE"
+    
+    # Find and rename the extracted file
+    if [ -f "merged.genesis.json" ]; then
+        mv "merged.genesis.json" "$MAINNET_GENESIS_PATH"
+    elif [ -f "merged.genesis.json.mainnet" ]; then
+        mv "merged.genesis.json.mainnet" "$MAINNET_GENESIS_PATH"
+    else
+        echo "❌ ERROR: Extraction failed (genesis file not found in archive)"
+        rm -f "$TAR_FILE"
+        exit 1
+    fi
+    
+    rm -f "$TAR_FILE"
+    echo "✅ Downloaded and extracted successfully"
+}
+
+# ==============================================================================
+# Mainnet Genesis Mode
+# ==============================================================================
+_prepare_mainnet_genesis() {
+    echo ""
+    echo "🌐 Mainnet genesis mode enabled"
+    
+    # 1. Enforce MIN_RUN requirement
+    if [ "$MIN_RUN" != "true" ]; then
+        echo ""
+        echo "❌ ERROR: Mainnet genesis requires MIN_RUN=true"
+        echo ""
+        echo "Reason:"
+        echo "  • Mainnet genesis is too large (6.6GB+)"
+        echo "  • Building op-program prestate would fail or timeout"
+        echo "  • Dispute game features are not compatible with mainnet data"
+        echo ""
+        echo "Solution:"
+        echo "  Set MIN_RUN=true in your .env file"
+        echo ""
+        exit 1
+    fi
+    echo "✅ MIN_RUN=true verified"
+    
+    # 2. Download genesis if not exists
+    _download_mainnet_genesis
+    
+    # Verify file size
+    GENESIS_SIZE_MB=$(du -m "$MAINNET_GENESIS_PATH" | cut -f1)
+    GENESIS_SIZE_GB=$(echo "scale=2; $GENESIS_SIZE_MB / 1024" | bc)
+    echo "✅ Found mainnet genesis ($GENESIS_SIZE_GB GB)"
+    
+    # 3. Validate configuration
+    if [ -z "$FORK_BLOCK" ] || [ -z "$PARENT_HASH" ]; then
+        echo "❌ ERROR: FORK_BLOCK and PARENT_HASH must be set"
+        exit 1
+    fi
+    
+    if [ -z "$CHAIN_ID" ]; then
+        echo "❌ ERROR: CHAIN_ID must be set"
+        exit 1
+    fi
+    
+    NEXT_BLOCK=$((FORK_BLOCK + 1))
+    echo ""
+    echo "🎯 Configuration:"
+    echo "   • CHAIN_ID: $CHAIN_ID"
+    echo "   • FORK_BLOCK: $FORK_BLOCK"
+    echo "   • PARENT_HASH: $PARENT_HASH"
+    echo "   • Next block: $NEXT_BLOCK"
+    echo "   • Test account: $TEST_ACCOUNT_ADDRESS"
+    
+    # 4. Process genesis using embedded Python (optimized for large files)
+    echo ""
+    echo "🔧 Processing genesis (this may take 1-2 minutes)..."
+    
+    mkdir -p "$CONFIG_DIR"
+    
+    # Run embedded Python script
+    python3 - "$MAINNET_GENESIS_PATH" "$CONFIG_DIR/genesis.json" "$NEXT_BLOCK" "$PARENT_HASH" "$CHAIN_ID" "$TEST_ACCOUNT_ADDRESS" "$TEST_ACCOUNT_BALANCE" << 'PYTHON_EOF'
+import json
+import sys
+import os
+import time
+
+def main():
+    input_file = sys.argv[1]
+    output_file = sys.argv[2]
+    next_block = int(sys.argv[3])
+    parent_hash = sys.argv[4]
+    chain_id = int(sys.argv[5])
+    test_account = sys.argv[6] if len(sys.argv) > 6 and sys.argv[6] else None
+    test_balance = sys.argv[7] if len(sys.argv) > 7 and sys.argv[7] else None
+    
+    # Load genesis
+    file_size_gb = os.path.getsize(input_file) / (1024**3)
+    print(f"   Loading genesis ({file_size_gb:.2f} GB)...")
+    
+    with open(input_file, 'r') as f:
+        genesis = json.load(f)
+    
+    account_count = len(genesis.get('alloc', {}))
+    print(f"   ✓ Loaded {account_count:,} accounts")
+    
+    # Update config fields
+    if 'config' not in genesis:
+        genesis['config'] = {}
+    
+    # Replace chainId with configured value
+    old_chain_id = genesis['config'].get('chainId', 'unknown')
+    genesis['config']['chainId'] = chain_id
+    print(f"   ✓ chainId: {old_chain_id} → {chain_id}")
+    
+    genesis['config']['legacyXLayerBlock'] = next_block
+    genesis['config']['jovianTime'] = 0  # Enable Jovian upgrade
+    genesis['parentHash'] = parent_hash
+    genesis['number'] = 0  # Required for geth init
+    
+    # Update timestamp to 15 minutes in the future (avoid conductor "unsafe head falling behind" error)
+    # This gives buffer time between init and service startup
+    current_timestamp = int(time.time()) + 15 * 60  # +15 minutes
+    genesis['timestamp'] = hex(current_timestamp)
+    
+    print(f"   ✓ legacyXLayerBlock: {next_block}")
+    print(f"   ✓ jovianTime: 0 (Jovian upgrade enabled)")
+    print(f"   ✓ parentHash: {parent_hash[:20]}...")
+    print(f"   ✓ number: 0 (required for geth init)")
+    print(f"   ✓ timestamp: {hex(current_timestamp)} (+15min from now)")
+    
+    # Inject test account (enabled by default in mainnet mode)
+    if test_account and test_balance:
+        if 'alloc' not in genesis:
+            genesis['alloc'] = {}
+        
+        account_key = test_account.lower()
+        if account_key.startswith('0x'):
+            account_key = account_key[2:]
+        
+        if account_key in genesis['alloc']:
+            print(f"   ⚠️  Account {test_account} exists, updating balance...")
+            genesis['alloc'][account_key]['balance'] = test_balance
+        else:
+            print(f"   💰 Injecting test account {test_account}...")
+            genesis['alloc'][account_key] = {"balance": test_balance}
+        
+        balance_eth = int(test_balance, 16) / (10**18)
+        print(f"   ✓ Test balance: {balance_eth:,.0f} ETH")
+    
+    # Write genesis.json
+    print(f"   Writing genesis.json...")
+    with open(output_file, 'w') as f:
+        json.dump(genesis, f, separators=(',', ':'))
+    
+    # Create reth version (number as hex string "0x0")
+    reth_file = output_file.replace('.json', '-reth.json')
+    genesis['number'] = "0x0"
+    
+    print(f"   Writing genesis-reth.json...")
+    with open(reth_file, 'w') as f:
+        json.dump(genesis, f, separators=(',', ':'))
+    
+    output_size_gb = os.path.getsize(output_file) / (1024**3)
+    print(f"   ✓ Output size: {output_size_gb:.2f} GB")
+
+if __name__ == '__main__':
+    main()
+PYTHON_EOF
+
+    if [ $? -ne 0 ]; then
+        echo "❌ ERROR: Failed to process mainnet genesis"
+        exit 1
+    fi
+    
+    # 5. Update rollup.json
+    _sed_inplace 's/"number": 0/"number": '"$NEXT_BLOCK"'/' ./config-op/rollup.json
+    
+    echo ""
+    echo "✅ Mainnet genesis prepared"
+    echo "   • Output: $CONFIG_DIR/genesis.json"
+    echo "   • Reth version: $CONFIG_DIR/genesis-reth.json"
+}