# Layer 2 Technology Comparison

## One-Line Positioning

| L2 | Positioning | Technology | Ecosystem |
|----|------|------|------|
| **Arbitrum One** | Largest TVL, DeFi hub | Optimistic Rollup (Nitro) | Mature, most protocols |
| **Optimism** | OP Stack standard, RPGF incentives | Optimistic Rollup | Public goods ecosystem |
| **Base** | Coinbase-backed, consumer apps | OP Stack (Optimism fork) | Fastest growth |
| **zkSync Era** | Leading ZK tech, native AA | ZK Rollup (zkEVM) | ZK ecosystem frontier |
| **Linea** | ConsenSys product, zkEVM | ZK Rollup | Enterprise backing |
| **Scroll** | Closest to EVM zkEVM | ZK Rollup | Research-oriented |
| **Polygon zkEVM** | Polygon ecosystem ZK direction | ZK Rollup | Polygon ecosystem |

---

## Technical Dimension Comparison

### Optimistic vs ZK Rollup

| Dimension | Optimistic | ZK Rollup |
|------|-----------|-----------|
| **Withdrawal to L1 Time** | 7 days (challenge period) | Minutes (after proof generation) |
| **Gas Cost** | Lower | Slightly higher (proof generation cost) |
| **EVM Compatibility** | Fully compatible | Near-complete (minor differences remain) |
| **Technical Maturity** | Mature | Rapidly developing |
| **Suitable Scenarios** | DeFi, general dApps | High-frequency trading, privacy, AA |

### Key Metrics Comparison (2024 Q4)

| L2 | TVL | Daily Transactions | Gas (ETH transfer) |
|----|-----|---------|---------------|
| Arbitrum | ~$15B | ~1M | ~$0.01 |
| Base | ~$10B | ~2M | ~$0.01 |
| Optimism | ~$7B | ~500K | ~$0.01 |
| zkSync Era | ~$3B | ~400K | ~$0.02 |

---

## Chain Selection Decision Tree

```
What type is your project?
│
├─ DeFi protocol (needs maximum liquidity)
│   → Arbitrum One (highest TVL, most DeFi integrations)
│
├─ Consumer application (social/gaming/NFT)
│   → Base (Coinbase user base, Onchain Summer ecosystem)
│
├─ Requires ZK features (privacy/AA/high-frequency trading)
│   → zkSync Era (native AA, most mature ZK ecosystem)
│
├─ Public goods/open source project (needs grants)
│   → Optimism (RPGF incentivizes public goods contributors)
│
└─ Multi-chain deployment (want to reach more users)
    → Arbitrum + Base + Optimism (OP Stack homogeneous, high code reusability)
```

---

## OP Stack Ecosystem (Important)

Optimism, Base, Zora, Mode, Redstone, etc. are all built on OP Stack, forming the **Superchain**:
- **Code reusability:** Contracts deployed on Optimism can migrate to Base with near-zero cost
- **Unified bridging:** Standardized inter-chain communication within Superchain (under construction)
- **Shared sequencer:** Planned for the future

```bash
# OP Stack chain contract deployment — same codebase
forge script Deploy.s.sol --rpc-url $OP_RPC --broadcast   # Optimism
forge script Deploy.s.sol --rpc-url $BASE_RPC --broadcast  # Base (nearly identical)
```

---

## Arbitrum Stylus (New Feature)

Arbitrum supports writing contracts in Rust/C++ (compiled to WASM), with 10x lower gas than Solidity:
```rust
// Writing Arbitrum contracts in Rust
#[entrypoint]
fn user_main(input: Vec<u8>) -> Result<Vec<u8>, Vec<u8>> {
    // Processing logic
}
```

---

## Cross-L2 Bridging Tools

| Tool | Supported Chains | Features |
|------|--------|------|
| **Across** | Major L2s | Fastest (minutes), low fees |
| **Stargate** | Multi-chain | LayerZero technology, deep liquidity |
| **Official bridges** | Native to each chain | Most secure, but slow (7 days/minutes) |
| **Hop Protocol** | OP ecosystem | Focused on OP Stack inter-chain |