Bitcoin has traded sideways between $77,100 and $81,300 over the past 20 trading days, with its current price near the range's lower support. Bitfinex Alpha said a break above $81,300 could encounter a volume vacuum and rapidly lift the price toward $86,500. Ahead of the Federal Reserve's interest-rate decision, options-market protection was shifted to contracts expiring on Sept. 18. Bitcoin volatility has declined even as altcoins have strengthened: all 29 major tokens rose last week, led by Polkadot's 43% gain and Zcash's 42% increase. Open interest in altcoin perpetual contracts (derivatives without expiry dates) exceeded Bitcoin's for the first time this week, a pattern that has historically accompanied a higher risk of market corrections.