Message v0 (Versioned Message)
Core Protocol · Deep
The versioned transaction message format introduced to support Address Lookup Tables (ALTs). Legacy messages inline all account addresses (32 bytes each), limiting transactions to ~35 accounts. Message v0 references ALT accounts by index, compressing the address list and allowing up to 256 accounts per transaction. Clients use VersionedTransaction with MessageV0 to build transactions that reference ALTs.