Solana activated Transaction V1 on testnet at epoch 1025 on September 1, expanding the maximum serialized transaction size from 1,232 bytes to 4,096 bytes, a 3.3x increase. The final testnet rehearsal ahead of the scheduled September 9, 2026, mainnet launch is designed to let zero-knowledge proofs, large multisignature transactions, confidential transactions and BLS signature schemes run as single atomic operations rather than across separate transactions or Jito bundles. SIMD-0296 sets the larger limit, while SIMD-0385 defines the V1 message format, moves resource configuration into the transaction itself and replaces V0’s Address Lookup Tables with inline address placement. Legacy and V0 transactions remain supported, but RPC providers, wallets, indexers, SDKs and analytics platforms must update their infrastructure. Anza requires RPC operators to move to Agave v4.2.2 or v4.3.0-beta.3, with non-compliant RPC consumers potentially facing failures when processing V1 traffic. The upgrade arrives as Solana’s stablecoin, tokenized-asset and DeFi activity expands, although the network’s 64-account limit remains unchanged.