Inside SyncSwap’s Low-Slippage Stable Pool

A constant-product route against two 1,000,000-unit reserves turns a 100,000-unit near-peg order into roughly 90,876 units out, while SyncSwap’s Stable Pool returns about 99,950 because its amplified invariant flattens the curve around balanced reserves. This reproducible comparison holds input, liquidity and a 0.04% fee constant; it isolates the pricing component rather than crediting chain speed or routing.

What happens to one stablecoin order?

The router and Stable Pool contract split the work. For an ERC-20 swap, the router transfers the input into SyncSwap’s Vault and credits it to the selected pool. The pool then observes the balance increase, prices the order, instructs the Vault to deliver the output and records the new reserves.

• The pool reads the input as its current Vault balance minus its recorded reserve.
• It obtains the applicable fee through Pool Master, then removes that fee from the input.
• Precision multipliers normalize tokens with different decimals before the invariant is evaluated.
• computeDFromAdjustedBalances fixes D; getY solves the output-side balance, and the difference becomes the fill.

The technical material behind Syncswap calls this a hybrid curve. That is the promise; the published contract supplies the mechanism: its StableMath library encodes an amplification coefficient of 1,000 and iteratively solves D and y instead of applying the Classic Pool’s direct constant-product quote.

Why is price impact small near $1?

Amplification makes the invariant’s center much flatter, so adding one pegged asset removes nearly one unit of the other while reserves remain reasonably balanced. In the test above, the fee-adjusted input is 99,960 units. The stable calculation loses only about 10.08 units to curve impact, or 0.0101%; the constant-product calculation loses about 9,083.97 units, or 9.0876%. Including the fee, total shortfall from a perfect 1:1 exchange is about 50.08 units versus 9,123.97.

This is not free liquidity. The curve concentrates pricing power around a fixed 1:1 relationship. As reserves diverge, it bends toward constant-product behavior, making each further trade more expensive and preserving some inventory instead of letting one side drain at a flat price.

The better fill transfers depeg risk

For correlated assets near parity, the design materially improves execution: the demonstrated 10% reserve-size order cuts curve impact by roughly 900 times under identical conditions. The trader receives the benefit. Liquidity providers bear the trade-off because arbitrageurs can leave the pool holding more of the weakening asset when one token breaks its peg. An amplification setting cannot distinguish temporary imbalance from insolvency.

What should a trader test live?

Compare quotes for the same stablecoin pair and input across Stable and Classic pools, then inspect the chosen route, fee, minimum received and post-trade reserves before signing. Repeat with progressively larger sizes. Near balance, Stable output should track the fee-adjusted 1:1 amount closely; as imbalance grows, the quote should deteriorate faster. That visible transition—not the “stable” label—is the evidence that the pool is protecting execution where its assumption holds.