# Combo Contracts

Combo contracts let you take a single position on the joint outcome of multiple existing contracts. A combo settles YES only if every leg settles YES — otherwise it settles NO. Each combo trades on its own continuous limit orderbook with its own deterministic ticker.

**Example:** A trader who believes BTC will be above $120,000 at year-end and ETH will be above $5,000 at year-end can combine:

- **Leg 1:** `GEMI-BTC-EOY26-HI120000` — YES
- **Leg 2:** `GEMI-ETH-EOY26-HI5000` — YES

Both are existing single-contract markets with their own independent orderbooks. The combo is a separate, third instrument that settles based on their joint outcome.

## Contract Specification

| Property | Value |
|----------|-------|
| Leg source | Existing contracts already listed on Gemini Predictions |
| Logic | AND only (at launch) |
| Leg direction | YES-side only (at launch) |
| Leg count | 2 minimum, configurable maximum |
| Settlement formula | Multiplicative — payoff is the product of leg outcomes |
| Settlement values | Each leg contributes 1 (settles YES) or 0 (settles NO) |
| Tick size | $0.01, same as single contracts |
| Price range | $0.01 – $0.99 |
| Trading hours | Same as the most restrictive underlying leg |
| Last trade time | When any leg enters its settlement window |

NO-side legs and OR / XOR / conditional logic are not available at launch and will be evaluated after launch.

## Ticker Format

Combo tickers are deterministic and content-addressable:

```
GEMI-CMB-{MMYY}-{HASH12}
```

| Component | Description |
|-----------|-------------|
| `GEMI` | Gemini namespace |
| `CMB` | Combo identifier |
| `{MMYY}` | Two-digit month and year of first creation |
| `{HASH12}` | 12-character hex hash of the canonical leg set |

**Example:** `GEMI-CMB-0526-A7F3B2C1D4E5`

## Pricing

The fair value of a combo under independence is the product of its leg prices:

```
P(combo) = P(leg₁) × P(leg₂) × ... × P(legₙ)
```

For example, a two-leg combo with legs trading at $0.60 and $0.70 has a fair value of $0.42 under independence. Correlation between legs (positive or negative) will move the market price away from this anchor; the orderbook reflects participants' collective view on the joint probability.

Because the same multiplicative formula governs settlement, there is no structural wedge between pricing math and settlement math.

## Settlement

### State machine

A combo proceeds through the following states based on the resolution of its legs:

- **Active** — At least one leg has not yet resolved, and no leg has resolved NO
- **Settled: YES** — Every leg has resolved YES
- **Settled: NO** — At least one leg has resolved NO
- **Voided** — At least one underlying leg has been voided

### Short-circuit resolution

The combo settles NO immediately upon the first leg resolving NO. Remaining legs do not need to resolve for settlement to complete.

This means traders holding a YES position in a combo can have it settle NO before the final leg's resolution date — for example, if a combo includes BTC above $120,000 at year-end and ETH above $5,000 at year-end, and BTC settles NO in December, the combo settles NO immediately even if the ETH contract hasn't reached its resolution date.

### Voided legs

If any underlying leg is voided by the exchange (e.g., due to event cancellation or data integrity issues), the combo voids and positions are unwound at the trader's entry price.

### Settlement value

| Outcome | Settlement value |
|---------|-----------------|
| YES (all legs settle YES) | $1.00 |
| NO (any leg settles NO) | $0.00 |

## Orderbook Behavior

Each combo is a distinct market with its own orderbook. Combos and their underlying legs are separate instruments and do not interact at the matching layer.

- **No cross-market matching.** Orders on A ∩ B ∩ C do not match against orders on A ∩ B or on the individual legs A, B, or C. Each combo is its own instrument with its own resting depth.
- **No duplicate markets.** If the same combination of legs already exists, requests route to the existing market rather than creating a new one.
- **Independent liquidity.** Each combo's depth and spread is independent of its underlying legs. Combos can be wider than their legs, especially for novel combinations.
- **Hedging surface.** Because legs are existing tradeable contracts, combo exposure can be hedged against the underlying single-contract orderbooks.

## Discovery

At launch, Gemini Predictions provides a curated set of pre-packaged combos. You can trade any combo in this set, but you cannot create custom combos — that capability is not available at launch and will be evaluated based on feedback.

The available combos are discoverable via API:

- Listing endpoints expose all active combo tickers alongside their leg breakdowns
- Market data feeds publish combo orderbook state on the same channels as single contracts
- Order entry treats combo tickers as first-class instruments

## API

Combo-specific endpoints:

| Endpoint | Description |
|----------|-------------|
| [`GET /v1/prediction-markets/combos`](/rest-api/prediction-markets/combos/list-combos) | List all active pre-packaged combos with leg breakdowns |
| [`GET /v1/prediction-markets/combos/{instrumentSymbol}`](/rest-api/prediction-markets/combos/get-combo) | Resolve a combo ticker to its full leg specification and per-leg resolution status |

## FAQ

**What contracts can be used as combo legs?**

Any contract currently listed and trading on Gemini Predictions can serve as a combo leg. Combos do not introduce new underlying instruments — they reference existing markets.

**Can I trade in and out of a combo before all legs resolve?**

Yes. Combos trade continuously on their orderbook until the combo settles. You can close a position at any time before final settlement.

**What happens to my position if one leg resolves early?**

If the early-resolving leg settles NO, the combo settles NO immediately. If it settles YES, the combo continues trading; remaining uncertainty now lies entirely with the unresolved legs, and the market price will typically re-price to reflect this.

**Can I create a combo with the same leg twice?**

No. Each leg in a combo must reference a unique underlying contract.

**Can combos include other combos as legs?**

No. Legs must be single contracts.

**Why does my order on combo A∩B not interact with my order on contract A?**

Combos and their underlying singles are separate instruments with separate orderbooks. Matching happens within each instrument's book independently. This allows the combo's market price to reflect joint-probability views distinct from the leg prices.

**Are combo fees different from single-contract fees?**

Combo fees follow the same schedule as single contracts. See the [fee schedule](https://www.gemini.com/fees/predictions) for details.

**If I hold a YES position on leg A individually and also hold a combo containing leg A, are those positions related?**

No. A combo and its underlying single contracts are independent instruments with separate positions. Holding YES on `GEMI-BTC-EOY26-HI120000` directly and holding YES on a combo that includes that leg are two distinct position entries. Settlement of the single does not net against or affect your combo position.