Solana is targeting September 9 for mainnet activation of Transaction V1, an optional format that raises the maximum serialized transaction size from 1,232 bytes to 4,096 bytes. The planned Wednesday upgrade gives developers about 3.3 times more room for instructions, signatures and data, allowing some large operations to be completed as one atomic operation rather than split into transactions that could partially succeed. Legacy and v0 transactions will remain valid under their existing limits, so wallets and applications do not need to migrate immediately. V1 removes Address Lookup Tables, relocates compute and priority-fee settings to transaction configuration, and retains the limit of 64 referenced accounts. RPC providers, indexers and explorers must support V1 to avoid request failures or incorrect fee information. Larger transactions use more bandwidth and may require higher optional priority fees during competition for processing capacity, but the upgrade introduces no separate fee based on transaction size.