Key concepts

Funding

A perpetual future has no expiry, so the exchange keeps its price near the spot price with funding: payments between longs and shorts, set by the gap between the perp's price and its oracle. When the perp trades above spot, longs pay shorts; below, shorts pay longs.

Phoenix computes SOL perp funding every hour and adds each hour's payment to a running total per unit of SOL, its cumulative funding. A position's funding over any stretch is the change in that total times the position's size. Tack reads the same total every Phoenix position is paid from.

SOL funding changes sign often. On Phoenix's SOL perp, daily averages changed sign 50 times between 19 November 2025 and 1 October 2026. A basis trade earning funding earns a different amount every hour, and some hours it pays.

Fixed and floating

A Tack swap turns that stream into a rate:

• The floating leg is SOL-PERP funding, as it comes.
• The fixed leg is a rate a year, K, agreed at the trade.

Rates in the app are in percent a year. The floating rate on the board is the funding of the last checkpoint, annualised.

Notional and reference price

The notional N is the size of a swap in USDC. The fixed leg is N × K a year.

The floating leg is funding on a fixed amount of SOL: N divided by the market's reference price, the SOL price when the maturity opened. A $10,000 swap in a market opened at $150 carries the funding of 66.67 SOL for its whole life. The floating leg explains why the amount of SOL, not the dollar figure, is held fixed.

Maturities

Each market ends at one maturity, a Friday at 08:00 UTC. Tack keeps three weekly maturities open. Trading stops when the last funding hour before maturity begins, and the funding record at maturity settles every swap for the last time.

Quotes and lots

A quote is a whole lot: a notional, a fixed rate, a side and the maker's collateral, posted to one maturity. Payers quote the rate they will pay; receivers quote the rate they want to receive.

A taker accepts a quote as it stands. Taking a payer's quote makes you the receiver, and the other way round. There are no partial fills and no automatic matching: two quotes that cross stay on the mast until someone takes one.

Collateral and margin

Both sides of a swap lock USDC. Initial margin is what a position needs to open; maintenance margin is what it needs to stay open. Both are the larger of a share of notional and a stress loss over the time left. Collateral and margin has the numbers.

Checkpoints and settlement

Each time Phoenix closes an hour of funding, its new cumulative total is written on chain as a checkpoint, numbered in order. Settlement applies checkpoints to a swap one after another and moves USDC between its two balances. Anyone can publish a checkpoint or settle a swap; Tack's crank does both after every funding record.

Position status

Once a position is not open, each side withdraws its own balance.