Circle Is Building Its New Blockchain to stop Quantum Attack

Circle’s Layer-1 blockchain Arc will launch at mainnet with an opt-in post-quantum signature scheme protecting users’ wallets from day one, as the USDC issuer warns that Q-Day could arrive by 2030 or sooner.

Circle’s Layer-1 blockchain Arc will debut at mainnet with an opt-in post-quantum signature scheme, making it one of the first blockchains designed from the ground up to withstand quantum computing threats. The announcement accompanied a detailed security roadmap published to the Arc blog this week.

Arc has been live on public testnet since October 2025, with Circle’s USDC as the native gas currency. USDC carries a market cap of roughly $77.5 billion, second only to Tether among stablecoins, and is the asset at the center of Arc’s institutional positioning.

At mainnet, users will be able to choose a signing method that future quantum computers cannot break, according to the Arc roadmap. The approach is deliberately opt-in, meaning no forced migration, no network-wide reset, and no assumption that every wallet or software stack will need to adapt immediately. Circle framed this as a practical path for institutions to begin protecting assets now, without disrupting existing developer tooling.

“Quantum resilience cannot live only in research papers, exploratory pilots, or distant roadmap slides. It has to show up in the infrastructure,” Circle said in its announcement.

Arc’s sub-second block finality also limits the attack window. In a so-called short attack, a quantum computer would need to derive a private key during the brief period between when a public key is exposed during a transaction broadcast and when the transaction is finalized. At under one second per block, that window is narrow.

A Three-Phase Plan Covering the Entire Stack

Circle’s post-quantum plan covers more than wallet-level protections. The near-term phase introduces quantum-resistant signatures at mainnet launch. The mid-term phase extends those protections to private balances, confidential payments, and recipient data, ensuring institutional financial activity stays shielded as quantum capabilities advance. The long-term phase targets validator authentication and off-chain infrastructure, including cloud servers, hardware security modules, and encrypted connections between nodes.

As crypto.news reported, Google recently moved its own post-quantum encryption deadline forward to 2029, citing faster hardware progress and improved error correction. Researchers from Google and the California Institute of Technology have warned that functional quantum computers capable of breaking existing cryptographic standards may arrive sooner than previous estimates suggested.

The Risk Is Already Partially Here

Circle pointed to two converging threats driving the urgency. The first is the eventual ability of quantum systems to forge transaction signatures directly. The second is already active: NIST has flagged “harvest now, decrypt later” tactics, where adversaries collect and store encrypted data today, intending to crack it once sufficient quantum capability exists.

“Long-term cryptographic durability is a baseline requirement that must be accounted for in infrastructure decisions being made today,” Circle said, directing its message explicitly at banks, fintechs, and enterprise platforms building on stablecoin infrastructure.