Does the Longest Chain Rule Apply to All Proof-of-Work Cryptocurrencies?

The longest chain rule, or a variant of it, is the foundational consensus mechanism for most Nakamoto-style proof-of-work cryptocurrencies, including Bitcoin. However, not all PoW systems use it exclusively.

Some newer PoW protocols, particularly those designed for faster block times, use modified consensus algorithms like the GHOST protocol (used by Ethereum before the merge) which consider both the length and the width of the chain (including some orphan blocks) to determine validity. This is an attempt to improve security and reduce centralization risk.