A fast swap is a token exchange on Ethereum that confirms in roughly 200 milliseconds — before the block that includes it has even been produced.

Standard Ethereum swaps work like this: you approve a token, submit a transaction, and wait for a block. That block takes 12 seconds. During that window, your transaction sits in a mempool, visible to searchers who may sandwich it, and you have no guarantee about when or where it will land.

Fast swaps eliminate the wait and the uncertainty.

How a fast swap works

1. Connect your wallet to Fast Protocol — any Ethereum wallet works
2. Select your tokens and amount — the interface shows you the expected output including mev rewards
3. Sign a Permit2 approval — a single signature authorizes the swap with no separate approval transaction and no extra gas
4. Your swap routes through FAST RPC to the mev-commit builder auction
5. A builder commits to inclusion — you receive confirmation in ~200ms
6. The swap settles on-chain in the next Ethereum block

From your perspective, the swap feels instant. You click, you sign, you see confirmation.

Permit2: no approval transactions

Traditional ERC-20 swaps require two transactions: an approval transaction (which costs gas and takes a full block) followed by the actual swap. Permit2 collapses this into a single off-chain signature.

How Permit2 works for swaps

• You sign a typed message that authorizes the exact token amount for this specific swap
• No on-chain approval transaction needed
• No unlimited allowance sitting in a smart contract
• One signature, one swap

This is both faster and more secure than the traditional approve-then-swap flow.

mev rewards and Miles

Many token swaps on Ethereum generate mev — the arbitrage and ordering opportunities created by your trade's price impact. On most platforms, searchers capture this value entirely.

On Fast Protocol, builders compete in an auction for the right to include your swap. This competition forces them to return value to you. At least 90% of the mev your swap generates comes back as an improved execution price. Swaps that generate mev also earn Miles.

Not every swap generates mev. Factors like pair volatility, liquidity depth, swap size, and market conditions determine whether extractable mev exists. A stablecoin swap in deep liquidity during calm markets may generate no mev — and therefore no mev rewards or Miles.

The earning is automatic when it occurs. You don't claim anything, stake anything, or interact with any additional contracts. The auction mechanism handles redistribution at the protocol level.

What tokens can I swap?

Fast Protocol supports swaps between major Ethereum tokens including ETH, WETH, USDC, USDT, DAI, and other liquid ERC-20 tokens. The available token list is displayed in the swap interface.

Swaps route through existing Ethereum liquidity — the protocol doesn't operate its own AMM or liquidity pool. Your trade executes against the deepest available liquidity on mainnet, with the builder optimizing routing as part of the auction.

Slippage and execution

Slippage is the maximum price movement you accept between quote and execution. If the actual output falls below your tolerance, the swap reverts instead of filling at a worse price.

Because fast swaps confirm in ~200ms, your window of price exposure is compressed from a full 12+ second block down to sub-second — so the tolerance you need is typically much smaller than on a standard DEX. Fast Protocol leans into that with an auto mode that keeps defaults tight.

Auto mode (default)

Auto mode picks the smallest tolerance that still lets the swap route reliably:

• 0.5% when you're selling ETH
• 1% when you're selling an ERC-20 token (the permit path carries slightly more routing overhead)

If the router reports that the route can't actually deliver within the base tolerance — for example, because gas has spiked or the pair is temporarily thin — auto mode bumps your tolerance up to 2% to cover the shortfall. When this happens, the confirmation screen shows a note: "Your slippage has been auto-adjusted to cover gas costs." You don't need to do anything; the swap still goes through at the original quote, just with more headroom.

Custom mode

For volatile pairs, large trades, or tokens with transfer taxes, you can switch to Custom and set any value from the path floor (0.5% or 1%) up to 50% — the same ceiling Uniswap uses.

A warning appears when your custom value goes above 5%:

Slippage above 5% is unusual. You will earn more miles, but will likely receive less tokens.

That tradeoff is real. Higher slippage tolerance means more price room for a builder to capture mev — which can increase your Miles earnings — but it also means your worst-case execution price is further from the quote. For ordinary swaps, stick with auto.

Deadline

The swap deadline (default 30 minutes) controls how long the signed order remains valid. If the transaction isn't included within that window, it expires instead of executing at a stale price. Because fast swaps confirm in ~200ms, the deadline is effectively just a safety net for network-level failures.