Polymarket specifics
Identifiers, tick sizes, minimum order size, mirror books, neg-risk events, and resolution detection.
Polymarket support is first-class but the venue has real quirks. Everything below was verified directly against Polymarket's live Gamma and CLOB APIs (June 2026); where behavior is non-obvious we say how we verified it.
Identifiers
| Form | Example | Notes |
|---|---|---|
| slug | fed-rate-cut-by-september | Human-readable; can change if the market is renamed. |
| condition id | 0x1fad72… (0x + 64 hex) | Stable; what PredArena stores as the canonical ticker on orders, trades, and positions. |
| CLOB token id | 76-digit decimal | One per outcome (YES and NO each have their own). |
Pass any of the three as ticker; condition ids and token ids auto-route to Polymarket without a venue field. Identifiers are case-sensitive — PredArena preserves them exactly (only Kalshi tickers are uppercased).
Trading rules that differ from Kalshi
- Minimum order size is typically 5 contracts (enforced per market from the venue's own
orderMinSize). - Tick size is 0.01 on most markets but 0.001 on designated high-volume markets — limit and trigger prices validate against the actual per-market grid.
- Prices are USDC; PredArena treats 1 USDC = $1 in portfolio accounting.
- PredArena trades whole contracts only (Polymarket itself permits fractional shares; we keep integer counts for cross-venue consistency).
- Some markets are viewable but not tradable (
enable_order_book=falseor paused order acceptance) — placement returns a clear 'not accepting orders' error.
Mirror books (verified)
Polymarket's NO-token book is an exact mirror of the YES-token book: every NO ask equals a YES bid at 1 − price with identical size, because minting/merging makes the two sides equivalent. We verified this empirically against live books (124/124 levels matched on a high-volume market) before relying on it. Practical consequence: fills on either side draw from the same underlying liquidity, and PredArena does not double-count it.
Negative-risk (multi-outcome) events
Multi-outcome 'winner-take-all' events use Polymarket's NegRiskAdapter: each outcome is still an independent binary YES/NO market, so orders and fills behave normally. What PredArena does NOT model is the cross-market NO-conversion trick (converting NO positions across sibling outcomes); if your strategy depends on neg-risk conversions, PredArena P&L will understate what is achievable.
Resolution & settlement
A market is treated as resolved when Polymarket marks it closed with a winning outcome (outcomePrices reaching 1/0, UMA resolution status). Open Polymarket positions are marked to the venue's last price between checks; settlement credits $1 per winning contract. Disputed or delayed UMA resolutions settle only when the venue's data does — never early.
Fees
See the Fees page for the verified category-based Polymarket taker schedule. Short version: takers pay a quadratic fee by category (0–7¢ multiplier equivalents); makers are never charged.