Toss, the South Korean fintech super-app run by Viva Republica, signed a Memorandum of Understanding with Optimism and Sunnyside Labs on July 8, 2026, to explore a Korean-won stablecoin built on the OP Stack.
Key Takeaways
- Toss (Viva Republica) signed an MOU with Optimism and Sunnyside Labs to explore a Won-backed stablecoin built on the OP Stack.
- Toss is the fourth regulated-finance name to build on the OP Stack in a year, after Bitpanda, Kraken’s Ink, and Mitsui & Co. Digital Commodities.
- The three-month proof of concept tests OP Enterprise settlement control, Korea-specific KYC/AML infrastructure, and Sunnyside Labs’ Privacy Boost for transaction privacy.
- Toss serves more than 30 million people, close to two-thirds of South Korea, as a daily financial control center.
- Privacy Boost conceals transaction histories and balances from outside view while still letting financial institutions retrieve the records they need.
What Happened?
Toss and Optimism will run a three-month proof of concept testing whether money can settle onchain while meeting Korea’s compliance, privacy, and control standards. Optimism provides the blockchain infrastructure, while Sunnyside Labs contributes the privacy layer. That layer keeps individual transaction details confidential on a public network.
Q-Ha Steve Kim, Chief Business Officer of Toss said:
OP Stack is the open-source software that also powers more than 30 other blockchains, including Coinbase’s Base, Kraken’s Ink, and Sony’s Soneium. Toss’s super-app model is same as Alipay and WeChat Pay models, though the compliance stakes here sit closer to a central bank.
Two-thirds of South Korea, more than 30M people, run their financial lives through Toss: banking, payments, investing, credit, taxes, all in one app.
— Optimism (@Optimism) July 8, 2026
Optimism and Toss just signed an MOU to explore putting the Won onchain. pic.twitter.com/8x25FjBC8K
Four Regulated Markets, One Piece of Infrastructure
Toss’s move is not an isolated experiment, according to Optimism. Toss is the fourth regulated-finance name in a year to build on the OP Stack, joining Bitpanda, Kraken, and Mitsui.
In Europe, per Bitpanda, the exchange announced Vision Chain, Europe’s first MiCA-compliant chain, built on the OP Stack. Kraken’s Ink was upgraded to OP Enterprise in the United States.
In Japan, Mitsui & Co. Digital Commodities built Zipangcoin, a tokenized gold, silver, and platinum product, on the same infrastructure. Four financial cultures reaching the same infrastructure choice in twelve months is the durable story. Toss is following a template, not pioneering a novel bet.
Why Toss Matters at This Scale?
Toss serves more than 30 million people, close to two-thirds of South Korea, for banking, payments, investing, credit, and taxes. Founded in 2015 with Korea’s first free peer-to-peer transfers, it now runs as a daily financial control center for 60% of the country.
South Korea is also one of the most crypto-engaged markets in the world, with an estimated 16 million people actively trading digital assets. That combination, a super-app with two-thirds penetration and a population already trading crypto, is the “market ready for it” case Optimism is making. It is not a hypothetical one.
South Korea has debated won-pegged stablecoin legislation for months without a settled framework. A private-sector proof of concept running ahead of that framework is itself notable.
The Three Validation Requirements
The proof of concept centers on three requirements Toss set for institutional-grade money:
- OP Enterprise: gives financial institutions direct control over how transactions are ordered and processed, the piece they care about most for settlement and compliance.
- KYC/AML infrastructure: know-your-customer and anti-money-laundering checks built to Korea’s requirements for digital asset transactions.
- Privacy Boost: Sunnyside Labs’ technology, keeping user financial data private on a transparent, auditable network.
That third requirement is the one that has stalled bank-grade stablecoins on public chains generally. Sunnyside Labs, described as Optimism’s official core developer, will supply the privacy technology for the trial. Privacy Boost securely conceals transaction histories and balances from outside view while still allowing financial institutions to access the transaction records they need.
It is also built to reliably process large-scale transaction volumes, making it suitable for servicing many customers simultaneously. That is a requirement Toss’s own user base makes non-optional, not aspirational.
CoinLaw’s Takeaway
This agreement reads as a compliance test dressed up as a partnership announcement. Toss did not sign on to launch a stablecoin. It signed on to find out whether a public rollup can satisfy what a Korean regulator would actually ask about.
That means settlement control, code-level KYC/AML, and whether customer data stays private on a chain anyone can inspect.
Optimism’s other three regulated deployments this year, spanning Europe, the US, and Japan, suggest the network has cleared versions of this bar elsewhere. The open question is whether Privacy Boost satisfies South Korea’s expectations at the scale of an app two-thirds of the country already uses. Regulators have not set that bar yet.
Toss brought more than 30 million subscribers and an estimated 16 million active Korean crypto traders into this test the day it signed. A pass would give that user base a template the company could pitch to regulators still finalizing won-stablecoin rules. A quiet non-renewal in three months would say more about Privacy Boost’s limits at that scale than any press release will.
