• The custody function of crypto platform Prometheum Inc. is now open for institutional clients.
• Prometheum had soft-launched with ETH and later added UNI and ARB to the assets it'll support, and this week the company said it'll also take custody of OP and GRT.
• Co-CEO Aaron Kaplan said Prometheum is trying to become the PayPal of crypto.

While the broader crypto industry fights with the U.S. Securities and Exchange Commission about the agency's labeling of most tokens as securities, Prometheum is swinging open its doors for a long-awaited test of its strategy to assume the SEC is right.

The company is now ready to accept institutional clients' holdings of Ethereum's ether (ETH) , Uniswap (UNI) and Arbitrum (ARB) , and it's added two more tokens: Optimism's (OP) and The Graph (GRT) . It opened its custody business on Wednesday after a previous soft-launch period, and the firm is on its way to starting a trading operation in the "very near future," said Benjamin Kaplan, the CEO of Prometheum Capital and Co-CEO of its parent company, Prometheum Inc.

Prometheum's untested advantage: It was the first fully registered crypto special-purpose broker dealer under the SEC's rules, and it's licensed for clearing and settlement, making it a potential one-stop shop as the business becomes fully operational. Until this week, that was a solitary status, but tZero Group Inc. said it got the same broker-dealer license and hopes to launch products next year.

However, much of the rest of the industry and prominent Republican lawmakers claim it's impossible to run such a crypto business under the existing securities laws, and Prometheum hasn't yet disclosed any customers or revenue to prove its critics wrong.

Kaplan said there's been "an immense amount of interest" from potential users and issuers.

"We're trying to be the PayPal of the digital asset industry," said Aaron Kaplan, who shares the CEO duty with his brother, in an interview with both Kaplans. He said there's no ecosystem at the moment that's set to be a compliant infrastructure for the "full life cycle" of securities products issued on-chain, which is especially important as interest rises for the tokenization of assets.

Prometheum Capital's addition of the tokens from Optimism, an Ethereum-based layer-two blockchain, and The Graph, a decentralized protocol for indexing and querying data from blockchains, was announced alongside the grand opening.

"This is just the beginning," Benjamin Kaplan said of the launch with five eligible tokens. "We're going to have quite a full vending machine."

The company does not yet have a public timeline for launching trading and settlement services.

Read More: Controversial Crypto Firm Prometheum to Treat Uniswap and Arbitrum's Tokens as Securities

When asked whether the company has had any clear conversations with the regulator over whether its approach is viable, Kaplan declined to detail interactions except to say Prometheum communicates with the SEC in the normal course of business.

An SEC spokesman declined a request for comment on the agency's view of Prometheum's custody operation.

The business' survival represents one of a handful of crucial industry tests, which would also include the outcome of a number of federal court battles. In Prometheum's case, if the SEC accepts its business model, that could prove it's possible to run a crypto platform under current laws, as argued by SEC Chair Gary Gensler. But if the SEC puts a stop to it, it counters the years-old argument from the agency that digital assets businesses need only comply with the laws to satisfy the agency.

Commodity Futures Trading Commission Chairman Rostin Behnam said in congressional testimony this year that a move from the SEC that validates Prometheum's treatment of ETH as a security will throw into question the longstanding position of CFTC-regulated firms that it's a commodity.

"We're not here to fight the battle between regulators," Benjamin Kaplan said. "We're proceeding under the federal securities laws as we believe it's the best framework to protect customers."