Stableswap on Solana - Swaps API Documentation

On Solana, Swaps’ stableswap protocol is a single on-chain program, deployed on mainnet:

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It swaps between 6-decimal stable mints:

Token	Mint
USDC	`EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v`
USDT	`Es9vMFrzaCERmJfrF4H2FYD4KCoNkY11McCe8BenwNYB`
PYUSD	`2b1kV6DkPAnxd5ixfnxCpjxmKwqjjaYmCZfHsFu24GXo`
xoUSD	`xoUSDq85Rjsb6SbUwJyreFgeWQvxdkT7R3c3g7s6p5Y`

Integration is permissionless at default rates read from pair_state. Custom pricing is delivered through Swaps-signed router proofs (covered below) — reach out to us to get set up.

Fees and `pair_state`

Each tradeable pair has a pair_state PDA holding directional fees, refreshed continuously by the Swaps pricing keeper:

Seeds: ["pair_state", mint_x, mint_y] where mint_x < mint_y (lexicographic pubkey sort — the lower-sorted mint is canonical X).
Fields: mint_x, mint_y, x_to_y_fee_bps, y_to_x_fee_bps, last_updated_slot, bump.

Read the pair_state for your pair to quote the default rate for each direction.

The `swap` instruction

swap(amount_in: u64, minimum_amount_out: u64)

Accounts, in order:

#	Account	Notes
1	`user`	Signer
2	`exchange_state`	Program state PDA
3	`mint_in`	Input mint
4	`mint_out`	Output mint
5	`token_state_in`	Token state PDA for the input mint
6	`token_state_out`	Token state PDA for the output mint
7	`token_vault_in`	Program vault for the input mint (writable)
8	`token_vault_out`	Program vault for the output mint (writable)
9	`user_token_account_in`	User’s input token account (writable)
10	`recipient_token_account_out`	Recipient’s output token account (writable)
11	`pair_state`	Pair fee state PDA
12	`instructions`	Instructions sysvar (used to read the router proof)
13	`system_program`
14	`associated_token_program`
15	`token_program_in`	Token program of the input mint
16	`token_program_out`	Token program of the output mint

An address lookup table is available to keep transactions compact:

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Custom pricing — the router proof

Without a proof, swaps execute at the default pair_state rates. A router proof — an Ed25519 signature produced by the Swaps router key — overrides the rate for a specific swap. This is how partners receive custom pricing. The proof is supplied as an Ed25519 signature-verification precompile instruction that must be at transaction instruction index 0; the program reads it through the Instructions sysvar. The signed message is 118 bytes:

Field	Size	Encoding
`"swap"`	4 bytes	ASCII
`user`	32 bytes	Pubkey
`mintIn`	32 bytes	Pubkey
`mintOut`	32 bytes	Pubkey
`amountIn`	8 bytes	u64 little-endian
`expiry`	8 bytes	i64 little-endian
`rateBps`	2 bytes	u16 little-endian

The stableswap-sdk npm package’s buildRouterProofMessage and buildRouterProofInstruction helpers are the reference implementation for this encoding. Proofs are signed by Swaps — contact us to set up custom pricing.

Errors

Error	Cause
`Frozen`	Exchange is currently frozen
`ZeroAmount`	Amount must be greater than zero
`InsufficientLiquidity`	Insufficient liquidity in the output vault
`SlippageExceeded`	Output is less than `minimum_amount_out`
`InvalidPairState`	Wrong `pair_state` account for the mints
`InvalidProof`	Router proof signature or message is invalid
`ProofExpired`	Router proof `expiry` has passed

Stableswap on EVM — the same protocol behind the GhostExchange interface.
Stableswaps via the API — the same liquidity through a single getAction call.

​Fees and pair_state

​The swap instruction

​Custom pricing — the router proof

​Errors

​Related

Fees and `pair_state`

The `swap` instruction

Custom pricing — the router proof

Errors

Related