Optimism

Optimism is the Ethereum Layer 2 behind OP Mainnet and the reference implementation of the OP Stack. It offers an EVM-equivalent place to use ETH and Ethereum-oriented wallets, contracts, and tools, while executing activity on Layer 2 and retaining a settlement relationship with Ethereum.

OP Mainnet separates fast L2 use from Ethereum withdrawals

OP Mainnet executes transactions on Layer 2 and publishes grouped transaction data to Ethereum, allowing nodes to reproduce the L2 chain instead of relying only on the operator for data. State commitments reach Ethereum without a validity proof attached to each submission.

Fault-proof dispute games give participants a route to challenge an incorrect commitment. An effective challenge requires client infrastructure, monitoring, and bonds, and the design includes a Guardian backstop and global pause. An L2 transaction can therefore be included and usable on OP Mainnet before its state has completed the fault-proof process needed for a withdrawal to Ethereum.

The full fee includes Ethereum data publication

An OP Mainnet charge combines Ethereum-style EIP-1559 execution gas with an L1 data fee for publishing the transaction’s share of rollup data to Ethereum. The data portion depends on compressed transaction size and Ethereum base-fee or blob-data pricing, so a small amount of local computation does not necessarily determine the total cost.

OP Stack chains can add a chain-configured operator fee after the applicable upgrade. Batches spread Ethereum publication costs across Layer 2 activity, but Ethereum congestion and blob pricing can still change what users pay. A fee estimate for the selected OP Stack chain is more useful than assuming all chains using the stack cost the same.

The Standard Bridge creates chain-specific token representations

The Standard Bridge links Ethereum and OP Mainnet bridge contracts through cross-domain messages. For a native ERC-20, it locks the asset on its native chain and mints the designated representation on the other side; the return trip burns that representation and unlocks the original asset.

A native asset can have more than one bridged representation, each with its own token contract, liquidity, and application support. A faster third-party bridge may use separate liquidity, relayers, or representations, so it is not simply the same transfer with different timing.

Starknet changes both the contract stack and proof route

Starknet is the clearest Layer 2 contrast. It uses Cairo contracts and STARK validity proofs that Ethereum verifies before accepting a state update, whereas Optimism keeps EVM equivalence and relies on fault-proof games for contested claims. Optimism favors Ethereum-tool continuity and OP Stack compatibility; Starknet requires a Cairo-oriented port and Starknet-native integration.