As an Ethereum Layer 2 rollup, Base inherits many similarities from Ethereum while improving scalability and costs. However, some technical and architectural differences exist between Base and Ethereum that developers should understand. This guide covers the key distinctions in opcodes, transaction types, fees, and more.

Overview of Base

First, let’s briefly introduce Base. Base is an Optimistic Rollup built by Coinbase and Optimism aimed at scaling Ethereum for mainstream adoption.

It reduces Ethereum's high fees and congestion while retaining Ethereum's security guarantees. Changes were minimized to maintain EVM equivalence - allowing existing Ethereum apps to migrate easily.

Now let’s explore some of the subtle technical differences.

Opcode Differences

Certain EVM opcodes behave differently on Base Layer 2 versus Ethereum Layer 1. For example:

• ORIGIN - Returns the aliased L1 address for L1-to-L2 messages
• DIFFICULTY - Returns a random value rather than block difficulty
• TIMESTAMP - Reflects L2 block time rather than L1

Developers should be aware of these discrepancies and avoid relying on the opcodes that vary between L1 and L2.

Accessing L1 State

While Base is an L2, smart contracts can access recent state from Ethereum L1 via the L1Block contract. For example, you can retrieve the latest L1 block hash, number, and timestamp.

This allows L2 contracts to verify recent L1 state if needed. This is usually unnecessary given L2's security guarantees.

Transaction Type Differences

Base supports legacy Ethereum transaction types along with L2-specific envelopes like:

• L1 to L2 transactions for bridging assets
• L2 to L1 transactions for withdrawing assets

These envelope types distinguish different cross-chain message payloads. Smart contracts can check tx.type to handle each accordingly.

Fee Structure

As an L2, Base has dual-fees - a low L2 execution fee paid in ETH or ERC20 tokens, plus an estimated L1 data fee paid in ETH.

The L1 data fee covers submitting transaction batches to Ethereum. This model differs from Ethereum's singular gas fee.

Faster Block Times

Base produces blocks every 2 seconds compared to Ethereum's ~12 seconds. This higher throughput allows supporting more transactions with consistent finality.

However, dApps should not rely on exact block times, as delays can occur during sequencing and finalization.

Limited Pre-155 Replay Protection

For security, Base does not support pre-EIP 155 transactions by default. This protects against transaction replay across chains - an issue before EIP 155 added a chainID.

Conclusion

While Base strives for EVM equivalence, developers should be aware of differences like altered opcodes, new transaction types, and the fee model. Most apps require minimal changes - primarily handling L1/L2 communication and fees.

Understanding the nuances smooths the process of leveraging Base for lower fees, higher throughput, and Ethereum-level security. The Base architecture balances migration simplicity with optimizations for cost, speed, and scalability.

Building for Base unlocks the ability to leverage Ethereum's network effects and liquidity while bypassing its limitations. The result is an L2 purpose-built for taking Ethereum mainstream and empowering the next generation of Web3 applications.

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