What changed
Arbitrum: one name, two eras.
The paper asserts a result and lets a challenger force a step-by-step dispute. The later network is an Ethereum rollup with its own client, data posting and upgrade keys.
Original thesis
A manager asserts a state. Anyone can challenge. The dispute narrows to a single step. The parent chain judges that step.
What changed
A live rollup adds who may assert, where the transaction data sits, how long the challenge window is, and who can upgrade the contracts. Those are operating facts. They are not in the 2018 proof.
What remains useful
The paper is the right citation for interactive fraud proofs. 'Arbitrum' alone is ambiguous. Say which document.