On-chain observers flagged unusual contract activity tied to Polymarket-linked infrastructure on Polygon, with outflows that appear to total more than $520,000. The activity was associated with addresses connected to the Polymarket UMA CTF Adapter, while an alleged attacker wallet and a related contract were also identified. Polymarket and UMA have not publicly clarified the incident details or whether users were directly impacted.

AmericanFortress published a cryptography paper describing a patent-pending, post-quantum signature method for hierarchical deterministic (HD) wallets. The design keeps existing BIP32-Ed25519 public keys and replaces the Ed25519 signing step with a ZK-STARK proof, aiming to avoid chain switches or mandatory fund migration. The paper also reports current performance figures, including sub-10-second signing proofs, 18–19 ms verification, and a fixed 218.4 KB signature size.

Polymarket is preparing a push into Japan by appointing Mike Eidlin as its local representative and starting a lobbying campaign, with the goal of receiving authorization to run prediction markets by 2030. The platform reported its first $10 billion monthly trading volume in March 2026 and said it reached 678,342 unique users in April as it rolls out updates such as Polymarket USD.

On May 21, 2026, the U.S. Securities and Exchange Commission said it is preparing a temporary regulatory exemption that would let eligible firms trial tokenized stock trading on blockchain networks under tight limits. The plan would test tokenized shares, automated market makers and crypto-native settlement, with conditions such as volume caps, whitelisted participants and time-limited approvals.

On May 21, 2026, Moonpay introduced Moonpay Trade, a cross-chain execution product designed to let institutions and enterprises connect to 200+ blockchains and protocols through a single API. The company says the Decent.xyz acquisition supplies routing and bridge infrastructure, while DFlow—reported to have processed over $12 billion in Q1 2026—extends coverage across Solana and EVM markets.

Blockchain.com has confidentially filed for a US initial public offering, signaling another attempt by infrastructure-focused firms to re-enter public markets. The company said on 21 May it submitted a draft Form S-1 to the US SEC for a proposed IPO of its Class A ordinary shares, without disclosing share count or valuation. The filing arrives as IPO discussions intensify across AI, fintech, and crypto infrastructure after a prolonged slowdown.

On May 21, 2026, the CFTC and the NHL signed a memorandum of understanding to coordinate against fraud, insider trading, and manipulation tied to NHL-related event contracts on federally regulated prediction markets. The pact sets up designated contacts and confidential information sharing, and it builds on the NHL’s October 2025 licensing deals with Kalshi and Polymarket that use official league data for contract settlement.

On May 21, 2026, Ripple Chief Technology Officer David Schwartz cautioned the XRP community about a sharp uptick in AI-enabled scam campaigns, including deepfake videos and fake giveaways. He said schemes often push bogus XRP airdrops that lure users into sending funds or connecting noncustodial wallets to malicious sites that can rapidly drain holdings. Schwartz also described a separate phishing effort aimed at Robinhood users that leveraged Gmail address tricks and emails designed to look authenticated.