StarkWare launches OffMarket to let Polymarket users trade more privately

StarkWare has launched OffMarket, a privacy service that lets users trade on Polymarket without publicly linking their positions to their accounts.

Polymarket records trades publicly on Polygon, allowing anyone to examine accounts' positions, order sizes, and trading histories. In 2024, blockchain analysts linked several accounts belonging to a French trader who had placed tens of millions of dollars in bets on Donald Trump winning the U.S. presidential election. More recently, Bloomberg reported identifying at least 34,000 trades flagged as possible insider activity between August 2025 and June 2026.

OffMarket uses zero-knowledge technology on Starknet and has been available in a limited release since August. Deposits are currently capped at $1,000 USDC per account, with StarkWare planning to adjust the limit according to demand and usage, a spokesperson told The Block. Orders are executed on Polymarket itself, against the same buyers and sellers and at the same market prices.

OffMarket is fully non-custodial, with users retaining control of their keys in their browsers, the spokesperson said. User funds sit in Starknet's open-source privacy pool, while Polymarket positions are held in its contracts under wallets derived from users' signatures. The spokesperson said users could recover their wallets using those signatures if OffMarket ever went offline. OpenZeppelin audited the pool contract in June and reported no critical or high-severity findings, and StarkWare formally verified the contract the following month, the developer said.

Starknet has previously introduced privacy features for other onchain assets. The Block reported in June that the network had launched its STRK20 privacy framework, allowing ERC20 balances and transfers to be shielded while retaining viewing keys for legally required disclosures. On Tuesday, StarkWare introduced Shadow Accounts, a new STRK20 feature that lets users interact with individual applications without publicly linking their activity to their main wallets.

StarkWare co-founder and CEO Eli Ben-Sasson, who was also a founding scientist of Zcash, said Wednesday that the project grew out of his longstanding work on financial privacy.

"Zcash, which is huge today, was born out of conviction by me and others that privacy matters and people would come to value it — even if it took years," he said in a statement. "That unwavering belief is exactly what drives us today as we bring zero-knowledge technology to Polymarket through OffMarket."

Polymarket and its U.S. platform generated a record combined $14.7 billion in trading volume in June amid FIFA World Cup fever, according to The Block's data, subsequently dropping to $12.9 billion in July, $8.4 billion in August, and $13 billion in September.

How OffMarket handles trades

Despite the privacy improvements, the StarkWare spokesperson confirmed that OffMarket still cannot prevent someone from identifying a trader through transaction size or timing. The markets, prices, and trades themselves remain public. USDC transfers from the shared pool to a fresh wallet are visible, as are any Polymarket trades from that address. It does not show who originally deposited the funds, though fewer people using the pool at once could make that easier to work out. OffMarket shares Starknet's existing privacy pool, which has around $1.5 million and 17,000 deposits, according to L2BEAT figures cited by StarkWare.

StarkWare did not provide user numbers or trading volumes for the limited OffMarket release. The spokesperson said volumes were small by design, with the early release subject to the $1,000 deposit cap. Private orders take about a minute to execute, while withdrawals take a few minutes. Polymarket's normal taker fee applies, with minimal additional network costs, the spokesperson said.

OffMarket is not a Polymarket product and has no formal partnership or special access to the platform. It is part of Polymarket's verified builder program, although Polymarket has the ability to disable its builder code, the spokesperson acknowledged to The Block. The spokesperson said StarkWare had not discussed the launch specifically with Polymarket, but that the platform was aware of the project and "happy" with it. OffMarket also applies Polymarket's geographic restrictions, including the ban on U.S. users.

Independent compliance firm Financial Privacy Inc. (FPI) keeps the master viewing key inside a secure enclave, according to StarkWare. The service screens deposits against sanctions lists, and FPI's counsel reviews requests for transaction information from courts, regulators, and agencies. The spokesperson told The Block that FPI can refuse a request if it cannot verify its legal basis, authenticate it, or confirm the requesting authority has the necessary powers. FPI only releases information covered by an approved request. The viewing key does not give FPI access to users' funds. StarkWare and FPI secure the key with a multisignature arrangement.