Overview

Binary options markets have two outcomes. A winning share pays 1.00 USDC; a losing share pays 0. Orders use the same transaction types and signing flow as other Lighter markets. See Signing transactions for client setup and transaction submission.

Up/Down markets compare an underlying asset’s Chainlink price at the start and end of an observation window. Each window has a new market. Up wins if the closing price is at least the opening price; otherwise, Down wins.

Discover listed series and their observation windows through events. The asset names and durations used in these guides are examples; read each series’ configuration from the API.

Core concepts

Concept	Binary options
Market	One order book per window. `market_type` is `binary_options`, symbol `<ASSET>-UPDOWN-<DURATION>-<WINDOW START>` (window start in Unix seconds), e.g. `ETH-UPDOWN-15M-1792436400`
Price	Price of one Up share in USDC, from `0.01` to `0.99` with a `0.01` tick (`price_decimals = 2`). It can be read as the market-implied probability of Up
Size	Number of shares. Read `size_decimals`, `min_base_amount` and `min_quote_amount` from each market returned by `events`. For example, mainnet markets checked on October 19, 2026 use four decimals, a 5-share minimum and a `0.000001` USDC quote minimum
Buy / Sell	Buying opens or adds to an Up position and costs `price × size`. Selling opens or adds to a Down position and costs `(1 − price) × size`. Trading the other side reduces your position first
Payout	`settlement_cap = 100` ticks (`1.00` USDC) per winning share, `0` per losing share, paid to the USDC balance at settlement
Collateral	Every order and position is fully funded from the USDC balance. No leverage, funding or liquidation
Operator	`operator_account_index` creates and settles the market. Lighter operates the Up/Down series

A market_id is never reused. Settled markets stay queryable, including their outcome.

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Use events to discover binary options markets. They are excluded from the unfiltered orderBooks listing and from orderBookDetails, even when a market ID is supplied to orderBookDetails. orderBooks?market_id=<id> does return an individual binary options market, but its fee fields read 0.0000; use the market fees returned by events. See Discover markets.

Integration guides

Guide	Covers
Discover markets	Events, market IDs, trading windows and underlying price candles
Trading and fees	Order parameters, collateral, restrictions and fee calculations
Positions and settlement	Account positions, settlement payouts and realized PnL
Partner attribution	Client approvals, integrator fees and reporting
WebSocket	Market statistics, underlying candles and existing account channels

Integration checklist

Discover tradable windows with events?tag=…&active=true&sort=start_at&order=asc. Cache each market's ID, trading window and decimals; refresh discovery as windows roll over.
If you charge partner fees, check that the client's ApproveIntegrator sets max_spot_taker_fee and max_spot_maker_fee at or above the rates you request.
Send limit or market orders with integer prices and sizes. Up/Down markets use prices from 1 to 99 and four decimal places for shares. Reduce-only, stop and TWAP orders are unsupported.
Stop submitting new orders when the trading window ends or the market leaves active. Track the market through settlement.
Read positions from bo_positions, settlement records from trades, and realized PnL from portfolio/boPnl.

Partners who want to create and settle their own binary options series need market slots assigned by Lighter. Contact the team to operate a series.