Skip to main content
Match settles USDC burn and mint demand through a periodic batch auction that prices a clearing fee in basis points. The auction never prices USDC itself; USDC always remains 1:1 with USD. Understanding the auction mechanics (how the clearing fee is set, how fills are allocated, and how unfilled remainder is handled) is foundational to participating effectively.

​
Auction cadence

Match runs on repeating cycles. Each cycle begins when the previous one closes and ends when the auction clears. Near the end of each cycle, a lock window opens before clearing.

​
Auction lifecycle

The following diagram shows the phases of a single auction cycle. Open phase: Participants submit new orders, modify existing orders (including cancellations and size changes), or improve their fee limits. Lock window: Before clearing, the auction enters a lock window. New orders and price improvements are still accepted, but cancellations and size changes are blocked. Attempting to make a fee less competitive during the lock window returns error 137005. This prevents last-second liquidity withdrawal. Clear: The auction engine sets a single uniform clearing fee and allocates fills. Settle: Filled burn-side orders receive USD to their Circle Mint account. Filled mint-side orders receive USDC. Unfilled remainder follows each participant’s post-fill election.

​
Uniform clearing fee

Every matched order in a given auction cycle clears at the same fee, expressed in basis points. There is no bespoke bilateral pricing. Burn-side participants pay the clearing fee; mint-side participants receive the corresponding rebate. The clearing fee never exceeds the fee cap.

​
Clearing objective

The auction engine determines the clearing fee by working through three objectives in priority order:
  1. Maximize matched volume. The engine finds the fee level that allows the greatest total volume to be matched between the burn side and the mint side.
  2. Minimize absolute imbalance. If multiple fee levels produce the same matched volume, the engine chooses the one with the smallest absolute difference between matched burn volume and matched mint volume.
  3. Prefer the higher fee on an exact tie. If two fee levels still produce identical matched volume and identical imbalance, the engine picks the higher fee. This is the minter-bias tiebreaker: it resolves the edge case by favoring the fee that benefits mint-side participants. In the extreme case where a pure market-vs-market tie produces no imbalance at any fee level, the auction resolves at the fee cap.

​
Allocation priority

After the engine sets the clearing fee, it assigns fills to individual orders in two passes:
  1. Price aggressiveness. Orders with limits more favorable than the clearing fee fill first. A burn-side order willing to pay 8 bps fills before one capped at 6 bps when the clearing fee is 6 bps.
  2. Pro-rata at the marginal price level. Orders whose limit equals exactly the clearing fee share the remaining available fill proportionally to their order size.

​
Self-match prevention

A participant cannot hold resting orders on both the burn side and the mint side of the same auction simultaneously. Attempting to do so returns error 137006 (HTTP 409). This rule prevents a single participant from matching against themselves.

​
Post-fill elections

When an order is only partially matched, the participant’s post-fill election determines what happens to the unfilled remainder.

​
Market orders

A market order has feeBps omitted or set to null. It carries no fee constraint and fills at any valid clearing fee the auction sets. Market orders are the most price-aggressive order type and receive first priority during allocation.

​
Order size constraints

All orders must be a minimum of 100andamultipleof100 and a multiple of 100. This granularity is required for integer-cent fee arithmetic during clearing.

​
Order status lifecycle

An order moves through the following statuses as it progresses through an auction cycle.