On a USD 10 million USD/MXN trade, one cent of markup is USD 5,000. Ten cents is USD 50,000.
Hold on to that. Most of what follows is about centavos, and about hours, which are centavos in disguise.
A USD 10 million USDC to MXN trade, step by step
A payments company has to fund merchant payouts in Mexico. It needs the pesos from USD 10 million in its Mexican account before Thursday. It is Tuesday, 3:14pm in Mexico City, 4:14pm in New York. The peso market is wide open.
The treasurer has two ways to do it.
How USD 10 million is converted to pesos by bank wire
The treasurer calls the bank's FX desk or hits the button on the portal. The bank shows one rate. One number. Not the market rate plus a markup, just the rate. The treasurer accepts. The dollars are debited.
A SWIFT message leaves for the bank's correspondent, the institution it uses to reach Mexico. From this moment the treasurer no longer controls anything. There is no status page.
Three compliance teams look at the payment: the sending bank, the correspondent, the receiving bank in Mexico. Any one of them can hold it for questions. Most days none do. Some days one does, and the treasurer finds out on Thursday when the pesos are not there.
Value date. The dollars-for-pesos leg settles through CLS, the system that makes sure both sides of an FX trade pay at the same time. T+2 by market convention. The pesos are credited to the company's Mexican account at some point during Thursday's banking hours, net of whatever the correspondent charged along the way. The treasurer sees a smaller peso number than expected and a line item that says "fees."
The pesos go out over SPEI to the merchants. That part takes seconds. SPEI was never the problem.
Elapsed: roughly 44 hours. For all of them, USD 10 million is nobody's. Not the company's, not the merchants'. In transit.
How USD 10 million in USDC is converted to pesos with Rio: an off-ramp with SPEI payout
The treasurer requests a quote for USDC to MXN, USD 10 million. Rio returns one all-in number against the live market rate, with the market rate and the spread shown separately. The quote is firm for the full amount for about ten seconds.
The treasurer accepts. The trade is booked at that price. Not "subject to confirmation." Booked. There is no last look, the bank practice of rejecting a trade after you accepted it. No re-quote. No taker fee or fiat in/out fee on top.
The treasurer sends USD 10 million in USDC from the company's own wallet to Rio's deposit address, on Solana this time (it could be Arc, Stellar, Polygon, Tron, Ethereum or Base). The network confirms in seconds. No correspondent. No SWIFT.
Rio's system sees the settlement land and pays the pesos out over SPEI, automatically, to the CLABEs the company whitelisted when it onboarded. Its own account, or straight to the merchants. The merchants have their pesos before the treasurer has finished reading the confirmation.
Elapsed: about 90 seconds. It is still Tuesday. The dollars were the company's until 3:14:40pm and the pesos were the company's from 3:15:32pm. The 44 hours did not happen.
The same flow runs backwards, by the way. Sell pesos, settle over SPEI, USDC lands in the whitelisted wallet. Any day of the week, any hour, except during SPEI's announced maintenance windows.
In Mexico, FX services are provided by Rampa Blockchain, S.A.P.I. de C.V., which performs operations with virtual assets as a vulnerable activity under Article 17, Section XVI of the LFPIORPI. Rio is not a direct SPEI participant. It settles through its own accounts at regulated Mexican banks.
Bank wire vs stablecoins: what changes for a treasury
Now put the two logs side by side and look for the money.
The exchange rate: what one centavo of markup costs on USD 10 million
On Road A the treasurer saw one number and had no way to know how many centavos sat between it and the market. On Road B the market rate and the spread were on the screen before the trade. You can argue about whether a spread is fair. You cannot argue about a spread you cannot see. And remember: ten centavos on this ticket is a million pesos.
Idle cash: the cost of settling two days later
USD 10 million out of working capital for two days, every time. A company moving USD 50 million a month in trades spread across the month has several million dollars permanently in transit. That money is not earning, not paying suppliers, not sitting as a buffer. It is in a correspondent's ledger.
Price risk between order and settlement
On Road A the rate was fixed on Tuesday and the pesos arrived Thursday. Someone carried the risk of USD/MXN moving in between, and that someone priced it into the rate. On Road B the price was locked at 3:14:08 and settlement was done by 3:15:32. There was no gap to price.
Hours: trading 24/7 versus banking hours
The Road A order worked because it was Tuesday afternoon. Had it been Friday at 6pm, the pesos would have arrived Tuesday or Wednesday. Road B does not care what day it is. Peso liquidity is thinner outside New York hours on every road, that is just the market, but on Road B the off-hours cost shows up in the quote before you trade, not on a statement after. Piece 03 in this series is about exactly that.
The Mexican peso market in numbers: size, rails and settlement
| Currency | Mexican peso (MXN) |
|---|---|
| Rules | Free float. No capital controls. No tax on FX trades. |
| Size | USD 153 billion a day. 14th most traded currency in the world, 3rd among emerging markets. 82% trades outside Mexico, 98% against the dollar. (Banco de México, BIS 2025 survey) |
| Peso rail | SPEI. 24/7, credits in seconds. |
| Bank FX settlement | T+2. T+1 when both banks allow it. |
| Stablecoin FX settlement | One to two minutes from the moment you send your settlement, seven days a week. |
| Regulators | Banco de México and CNBV. Stablecoin conversion is supervised under Mexico's anti-money-laundering law (LFPIORPI). |
| Stablecoins | USDC, USDT |
| Networks | Solana, Arc, Stellar, Polygon, Tron, Ethereum, Base |
Where does the dollar-peso exchange rate come from?
The peso is a dollar market. 98% of it trades against USD, and most of that happens in New York and London, not Mexico. The rate on any screen is a reference that comes from the big banks trading with each other. Every layer between those banks and your account adds centavos, and the number of layers is not the number of competing prices. Two banks that show you the same rate to the fourth decimal are not competing for your business. They are passing along the same quote.
How to evaluate a stablecoin FX provider: four questions
A tight spread on a screen means nothing by itself. These separate a liquidity provider from a middleman reselling someone else's price. Copy them into an email.
- Is your price firm or indicative, and for how long? A price that moves when I try to hit it is not a price. (Rio: firm for the full amount for about ten seconds, no last look.)
- Up to what size does the price hold? A quote good to USD 500 thousand that degrades on every slice after that is useless for a USD 10 million ticket. What size is behind the number?
- How do you handle an order big enough to move the market? The right answer is a TWAP, splitting the order across a time window so I get close to that window's average price instead of one instant's. Do you offer it?
- What happens when you have flow the other way? A desk with some clients buying pesos and others selling can match them internally. Traders call it an axe, and when it happens the desk can price well inside its normal spread. Do you alert clients when you have one?
How much a remittance network saved by converting with stablecoins
One of the largest remittance networks in the world moved most of its Mexico FX flow onto Road B and measured a saving of about 30% against its previous banks, with settlement in minutes instead of days. The saving came from the rate, the hours and the gap together, not from any one of them.
FAQ
Why does bank FX into Mexico settle two days later?
T+2 is the standard settlement cycle for USD/MXN in the interbank market, and CLS settles on that value date, not on the trade date. It removes the risk that one side pays and the other does not. It does not make the cycle shorter. With Rio the price is locked when you accept and the payout follows within minutes of your settlement, because both the stablecoin and SPEI run around the clock.
Is stablecoin conversion more expensive outside market hours?
Peso liquidity thins outside the New York session and over the weekend, and spreads widen on every road, bank or stablecoin. The difference is that a firm all-in quote shows you the off-hours cost before you execute, so you can decide whether to trade now or wait for the open. Piece 03 covers the hour-by-hour picture.
What does "firm price" mean in practice?
A price the provider has to honor for the quoted amount during its validity window. The opposite is an indicative price, which can change at confirmation, or a quote with last look, where the provider can reject the trade after you accept. Rio's quotes are firm for about ten seconds for the full amount, no last look.
What is a TWAP and when does it make sense?
Time-weighted average price. A large order is split into slices across a set window so your fill lands near the window's average rather than one instant's price. Use it whenever a single ticket is big enough to move the market against you if crossed at once. For MXN outside US hours, that can happen well below USD 10 million.
Which networks can the settlement arrive on?
Solana, Arc, Stellar, Polygon, Tron, Ethereum and Base, in USDC or USDT. The network affects how fast your settlement confirms and what the network fee is. It does not affect the FX price, which is quoted against the market rate regardless of network. Details in the developer docs.
What is Rio?
Rio is stablecoin FX infrastructure for Latin America. It provides liquidity, conversion and payout to local rails in Mexico, Colombia and Peru for fintechs and enterprises, with all-in pricing against the market rate, firm quotes for the full amount and settlement in minutes. Rio processes USD 12 billion in annualized volume.
In Mexico, FX services are provided by Rampa Blockchain, S.A.P.I. de C.V. Rio is a technology company, not a bank, and does not take deposits.
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