Token-2022 extensions are optional modules added to a token at creation time that enable advanced functionality not available in the standard SPL token. Extensions are defined in the Solana Program Library and each adds specific capabilities to the token.

Available extensions include: Transfer Fee (collect a percentage of each transfer), Interest Bearing (tokens that accrue interest over time), Non-Transferable (tokens that cannot be moved between wallets), Permanent Delegate (an irrevocable authority over all token accounts), Metadata (on-chain name and symbol), and Confidential Transfers (privacy-preserving transfers using zero-knowledge proofs).

Extensions are immutable in most cases — once set at token creation, they cannot be changed. Projects must carefully design their tokenomics before deploying a Token-2022 token with extensions.