ERC-2309 (Consecutive Transfer Extension)

ERC-2309, titled ERC-721 Consecutive Transfer Extension, was written by Sean Papanikolas in October 2019 and is marked Final. It solves a concrete gas problem: emitting one Transfer event per token makes it unfeasible to create or transfer large quantities in a single transaction, because complexity grows linearly and exhausts the block gas limit.

The standard defines one event, ConsecutiveTransfer, with four parameters: fromTokenId (the first ID in the range), toTokenId (the last ID in the range), fromAddress (the sender, which is the zero address when minting) and toAddress (the receiver, the zero address when burning). The fromTokenId, fromAddress and toAddress parameters are indexed, while toTokenId travels in the data part of the log. With a single emission, indexers and marketplaces get a standard way to determine ownership of large collections without walking thousands of individual events.

It should not be confused with ERC-721A, introduced by the Azuki team in January 2022. They are distinct standards that complement each other: ERC-721A gets its main savings by another route, by not writing each token's owner to storage during a batch mint, and it can lean on the ERC-2309 event for mega-mints at contract deployment, a use ERC-2309 explicitly permits. OpenZeppelin added ERC-2309 support to its contracts. The gas comparisons in circulation are technical figures, not market ones, and are best taken as approximate.