Toss and Optimism sign MoU for a 3-month Korean won stablecoin PoC for institutional payments

Viva Republica, the operator of South Korea-based mobile money transfer app Toss, has reportedly signed a memorandum of understanding with Optimism and Sunnyside Labs to test whether a Korean won-based stablecoin can work for domestic financial institutions. For PSPs and acquirers, the interesting part is not the token branding; it is whether settlement control, KYC (know-your-customer), AML (anti-money laundering), and privacy can be made to work on a public blockchain.

1. According to Yonhap News, the three companies will run a three-month proof of concept (PoC) using Optimism’s OP Stack and Sunnyside Labs’ Privacy Boost protocol. The goal is to develop a Korean won-based stablecoin and test whether the setup can be used as payment infrastructure for financial institutions in South Korea.
2. The PoC is set to examine three practical questions that matter to regulated payment flows: whether financial institutions can control the settlement process, whether KYC and AML requirements can be implemented, and whether transactions can remain private on a public blockchain ledger. In other words, the project is trying to make “public blockchain” and “institutional payments” sit at the same table without one swallowing the other.
3. Toss plans to use the three-month trial as the basis for building compliant stablecoin-based payment infrastructure in South Korea, according to the report. Optimism will provide the blockchain infrastructure, while Sunnyside Labs will provide the privacy-preserving technology to shield transfers.
4. Sunnyside Labs is described as a core developer for the Optimism Collective and has been building core OP Stack infrastructure. Toss, headquartered in Seoul and launched in 2015, says it has more than 30 million users on its mobile application.
5. The PoC comes after other major South Korean payments players have also moved into stablecoin testing. In late April, Shinhan Card partnered with the Solana Foundation to test the commercial feasibility of stablecoin payments and non-custodial wallets after completing a joint pilot project earlier that month. Late last year, Visa launched USD Coin (USDC) settlement services for some US-based financial institutions on the Solana blockchain, while Mastercard and South Korea’s BC Card are also exploring stablecoins for payments and settlement.

For high-risk merchants and PSPs, the signal here is straightforward: stablecoin pilots are no longer limited to crypto-native firms. Large consumer and card-payment operators are now testing whether blockchain rails can handle regulated settlement without breaking the compliance stack.