Constant zebra_chain::block::serialize::MAX_BLOCK_BYTES

pub const MAX_BLOCK_BYTES: u64 = 2_000_000;

The maximum size of a Zcash block, in bytes.

Post-Sapling, this is also the maximum size of a transaction in the Zcash specification. (But since blocks also contain a block header and transaction count, the maximum size of a transaction in the chain is approximately 1.5 kB smaller.)