What's the cheapest way, gas-wise, to modify a transaction to send tokens from 1 to 2 addresses? For example, is there a way where sending ETH to 2 addresses costs less than 42000 gas? Is it easier to amortize if you use WETH (or another ERC20)?

Have you looked into sending it from a safe wallet and bundling the transaction?

Alternative: if you were sending from a contract that supported permit style approvals, could give signatures to recipients and have them pull.

Eth transfers have a minimum gas amount (can be higher if transferring to a smart contract). So you can’t beat that. If the number of recipients is high, and transactions are frequent, a splitting contract where each party withdraws will distribute gas costs.

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