SOL 15-Minute Polymarket Up/Down Fair-Value Lag: Price the Binary From the Binance SOL Perp's Move Since the Window Open and Its Realized Vol, Buy the UP Token Only When Expected Value Net of the Polymarket Taker Fee and Spread Clears a Threshold, Hold to Settlement (POLYMARKET sol-updown-15m + SOLUSDT.BINANCE 1-MINUTE signal leg)

Original Research Lead hypothesis (archetype 1 of the prediction-market playbook: crypto signal to binary pricing). Polymarket lists a new 'Will SOL be up over the next 15 minutes?' binary every 15 minutes (series sol-updown-15m). It resolves UP if the SOL price at the window's end is at or above the price at its start. Once a window has run for a few minutes, its fair probability is close to a closed-form function of two numbers we hold at 1-minute resolution from Binance: the log move of SOL since the window opened and SOL's short-horizon realized volatility. Under a driftless random walk, P(UP) = Phi( ln(S_t / S_0) / (sigma_1m * sqrt(tau)) ), where S_0 is the SOLUSDT.BINANCE perp 1-minute close at the market's start_ns, S_t is the latest closed perp 1-minute bar, tau is the minutes left to resolution and sigma_1m is the EWMA standard deviation of 1-minute log returns over the trailing vol_lookback_min minutes, floored at 0.0005. The hypothesis is that the retail-dominated 15m binary book reprices more slowly than the Binance perp, which leads crypto price discovery. When SOL has moved decisively within the window, the UP token's last price still lags the fair probability by more than the fee and spread. We buy the UP token and hold it to settlement. Settlement is free, so the taker fee is paid only once. Long-only by construction: the venue is CASH, and 'betting DOWN' would be the complement series, which this test deliberately leaves out to keep a single pre-registered series. Instruments: the tradeable series is expanded by PolymarketSeriesStrategy from the spec {series: 'sol-updown-15m', outcome: 'Up', lookback_days: 60}. The placeholder instrument is SOL-UPDOWN-15M-0-UP.POLYMARKET; the bar type is its 1-MINUTE-LAST-EXTERNAL. SOLUSDT.BINANCE 1-MINUTE bars are listed in extra_instruments as the signal source only and are never traded. Data age: collection began 2026-08-13. The catalog holds resolved SOL 15m markets from 2026-08-12 to 2026-10-17 (about 66 days, about 6,000 markets), so lookback_days 60 can be filled. Venue and corpus choice: POLYMARKET has 2 of 4,834 experiments, and both prior Polymarket runs ended data_unavailable before any trade, so this mechanism has never been measured here. SOL is used instead of BTC to avoid the BTC-heavy corpus. The design is cross-venue (POLYMARKET + BINANCE), short-horizon (1-minute bars, holds of 15 minutes or less), event-driven, and uses no supplementary feed. It is materially different from the two data-blocked predecessors. The BTC 1H near-expiry harvest and the 15m late-window near-certainty harvest both bought only the favored side in the final minutes. This rule trades mid-window (minutes 3 to 10 of 15), at any probability in a bounded band, gated on fee-adjusted expected value rather than on near-certainty. Fee arithmetic (rate 0.07 on crypto up/down): buying at price p costs 0.07 x (1 - p) per dollar staked (2.8% at p = 0.60, 1.75% at p = 0.75), plus about 0.5% half-spread on entry; there is no exit fill. The expected return per dollar is (q - p) / p, where q is the model fair probability. Entry requires (q - p) / p - 0.07 x (1 - p) - 0.005 >= min_net_edge (baseline 0.05). For example, at p = 0.60 that means q >= 0.66; at p = 0.75 it means q >= 0.80. If half of the modelled gap is real, the realized net per trade is about +2.5% to +4% of stake. That is well above the roughly 1% round trip a spread-dominated binary venue costs.