Stableswap (StableSwapNG) Pool Standard

The StableSwapNG Pool Standard is the foundational AMM specification for Curve's stablecoin pools, representing the next-generation evolution of the original Stableswap invariant. It defines the mathematical formula that combines a constant-sum invariant for low-slippage trading near the peg with a constant-product invariant to ensure liquidity at all prices. The 'NG' (Next Generation) architecture introduces a gas-optimized implementation, dynamic fee logic, and a factory-deployed pattern that allows permissionless pool creation for any set of pegged assets.

Operationally, the standard specifies the get_dy and exchange interface that aggregators, trading bots, and wallets must integrate to correctly route stablecoin swaps. A key technical component is the amplification coefficient (A), which is now dynamic and can adjust based on pool conditions to tighten or loosen the spread around the peg. The standard also defines the get_virtual_price method, which is critical for lending protocols and yield aggregators to accurately value LP tokens as collateral. Integrators must handle the new fee getter, which returns a dynamically calculated fee that can change per-block based on the pool's internal balance and the offpeg_fee_multiplier.

For protocol architects and risk teams, the StableSwapNG standard introduces a new trust model for factory-deployed pools. Unlike the original Stableswap, where pools were often deployed individually and verified against a canonical bytecode, the NG factory pattern means that pool logic is a child contract of a verified factory. Auditors and integrators must verify the factory's immutability and the correctness of the find_pool_for_coins lookup. Chainscore Labs can assist teams with an upgrade readiness review, ensuring that smart contract integrations, oracle consumption, and LP token valuation logic are correctly aligned with the StableSwapNG interface before mainnet deployment.

The StableSwapNG pool standard is defined by its core invariant, which mathematically combines a constant-sum formula for near-parity assets with a constant-product formula to prevent pool drainage. This creates an amplified bonding curve that concentrates liquidity tightly around the current price, enabling low-slippage swaps between stablecoins or like-kind assets. The A (amplification coefficient) parameter governs the concentration depth: a higher A flattens the curve, reducing slippage for small trades, while a lower A increases slippage and protects LPs during volatility. In StableSwapNG, the A parameter is dynamic and can be adjusted by the pool admin or factory logic, allowing the pool to adapt to changing market conditions without a full migration.

A critical operational component of StableSwapNG is its dynamic fee logic, which replaces the static fee model of earlier Curve pools. The pool can programmatically adjust swap fees based on the current state of the pool's balance, specifically targeting deviations from the peg. When the pool becomes imbalanced, the fee increases to disincentivize further trades that would exacerbate the imbalance and to compensate LPs for the increased inventory risk. Conversely, fees decrease when the pool is near equilibrium to encourage arbitrage and restore the peg. This logic is implemented via the _dynamic_fee() function, which calculates the fee as a function of the pool's current balance deviation, an offpeg_fee_multiplier, and a base fee. Integrators must query the fee() method before routing trades, as the fee is not a constant.

For builders and risk teams, the dynamic fee model introduces a state-dependent cost that aggregators and trading bots must simulate before submitting transactions to avoid reverted trades or unexpected slippage. Auditors reviewing StableSwapNG pools should verify that the dynamic fee cannot be manipulated through flash loans or multi-block attacks to unfairly penalize LPs or traders. Chainscore Labs can assist integration teams in modeling the fee surface against historical volatility, reviewing factory-deployed pool parameters, and ensuring that off-chain pricing engines correctly consume the dynamic fee to prevent MEV leakage.