The basis accumulated over the weekend does not vanish instantly when U.S. stocks open on Monday. Instead, it gradually converges through adjustments via funding rates and two-way operations by cross-market arbitrageurs, typically taking several hours to a day. The convergence process is mechanism-driven, not an instantaneous event.
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1. What Causes Weekend Basis
Stock perpetual contracts develop a basis (the difference between the contract price and the spot price) over the weekend primarily because the pricing mechanism switches.
Coinbase's official documentation details this mechanism: during normal U.S. stock trading hours (Sunday 20:00 to Friday 20:00 ET), the index price for perpetual contracts is based on direct stock price sources (from Pyth and Blue Ocean ATS). But when weekends and holidays arrive and traditional markets close, the index price switches to an internal index—composed of a 1-hour exponential moving average (EMA) of the contract's mark price, anchored to the last trading price on Friday, with a cap of 3% (for indices) or 5% (for individual stocks).
In simple terms: the price you see over the weekend is a model-calculated 'shadow price,' not an actual traded price. Any deviation between the model price and Friday's closing price becomes the main source of the weekend basis.
2. How the Basis Converges After Monday's Open
Convergence is not a one-shot deal; it's the result of multiple mechanisms acting simultaneously.
① Automatic Index Pricing Switch
At 20:00 ET on Friday, it switches to the internal index; at 20:00 ET on Sunday, it switches back to direct stock price sources. In Coinbase's design, there is a 30-minute linear 'bridging' process starting Sunday at 20:00 ET, smoothly transitioning the index back to direct stock prices to reduce jumps between the weekend model price and real-time stock prices. This means convergence begins on Sunday night, not when the U.S. market opens on Monday.
② Continuous Correction via Funding Rate Mechanism
Stock perpetual contracts use the same funding rate framework as standard perpetual contracts. The larger the basis, the more the funding rate deviates from neutral, forcing arbitrageurs to step in and pull the price back toward the index. Funding rates settle every 8 hours (some platforms have moved to 4 hours). After pricing authority switches from the model back to the market, the corrective effect of the funding rate gradually becomes apparent.
③ Cross-Market Arbitrageurs Enter the Fray
When the underlying stock opens on Monday, the core driver of basis convergence comes from arbitrageurs.
A trader's review of an SK Hynix arbitrage shows that over the weekend, he noticed that the SK Hynix perpetual contract on Binance was $30 more expensive than on Hyperliquid (spread during the underlying stock's market closure). He judged that the spread came from different funding rate rules across platforms, built a position, and waited until the stock opened on Monday. The spread converged, and after deducting funding fees, he netted $15,000.
The spread convergence process is not instantaneous. The trader's review mentions that when the Binance contract was more than $40 above the spot stock, he bought Korean spot shares and simultaneously shorted the premium perpetual contract, hedging both directions: 'waiting for the spread to converge while collecting funding fees.' How long did he wait? From building the position over the weekend until the spread converged after Monday's open—this means convergence took several hours, not the very second of the opening.
3. Actual Speed of Basis Convergence
Arbitrageur validation provides a reference: when the Binance contract was $30 above Hyperliquid, the trader built a 1,000-share position and noted, 'the spread converged when the underlying stock opened on Monday.' The exact number of minutes after the open was not disclosed, but from the description, the correction of the spread occurred during Monday's trading session, not in the pre-market minutes.
Another case involves a mismatch between a Hong Kong leveraged ETF and crypto contracts. When the Korean market was closed on Friday but Hong Kong was open, a 2x long SK Hynix ETF listed in Hong Kong fell over 20% in a single day (equivalent to the underlying stock dropping more than 10%), while crypto perpetual contracts for the same stock only fell 5%. The trader bought the discounted ETF, shorted the SK Hynix contract on Binance, and waited for the spread to converge after the Korean market opened on Monday. This convergence also spanned a weekend plus Monday's opening window.
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4. Practical Tips: Three Signals to Watch Before Monday's Open
Step 1: Check if the weekend basis began bridging on Sunday night
What to do: Around 20:00 ET on Sunday (8:00 a.m. Beijing time Monday), observe whether the perpetual contract price has started to converge toward Friday's closing price.
How to do it: In Coinbase's mechanism, a 30-minute linear bridging starts at 20:00 ET on Sunday evening, smoothly transitioning the index back to direct stock prices. If the basis noticeably narrows during this period, the regression mechanism has activated.
Completion criteria: You have confirmed whether the basis showed any convergence action on Sunday night.
Step 2: Observe the convergence speed of the spread after Monday's open
What to do: After U.S. markets open on Monday, compare the change in the gap between the perpetual contract price and the spot price.
How to do it: If the spread rapidly narrows to a normal range (typically 0.1%–0.3%) within 1–2 hours after the open, it indicates that arbitrageurs and the funding rate mechanism are working effectively. If the spread remains above 1% with no significant narrowing, the contract's arbitrage mechanism may be impaired (e.g., insufficient liquidity, reduced market maker activity).
Completion criteria: You have assessed whether the contract's basis convergence efficiency is normal.
Step 3: Check if the abnormal weekend basis has completely disappeared
What to do: After the U.S. market close on Tuesday, compare the contract price with the spot price again.
How to do it: If the basis has returned to a normal range (close to the funding rate neutral level), the weekend effect has been fully corrected. If the basis still deviates significantly, the contract may have structural issues (e.g., insufficient depth, platform rule differences).
Completion criteria: You have confirmed whether the weekend basis has been fully absorbed.
Prerequisite: You are monitoring or trading a stock perpetual contract and have observed the weekend basis phenomenon.
Risk Warning: Establishing large positions during the weekend in low-liquidity after-hours or Asian sessions may expose you to a one-time price correction at Monday's open. According to OneKey's analysis of U.S. stock perpetuals, weekend candlesticks may only reflect 'a few large orders pushing on thin books' and do not represent actual supply and demand. When the U.S. market opens on Monday, prices tend to revert to the spot reference price, and 'positions chased over the weekend will first suffer a one-time correction.' If the direction at Monday's open is opposite to your position, basis convergence itself will not protect you from directional losses. Moreover, cross-border arbitrage involves foreign exchange risk—when this trader settled accounts, he lost $60,000 on foreign exchange alone.
After completing the above observations, how do you confirm the basis has converged?
After the U.S. market close on Monday, open your trading platform and compare the perpetual contract price with the stock price—if the spread has fallen from the weekend peak back to a normal range (usually 0.1%–0.3%), the basis has largely converged. If the spread is still significant, check whether the contract's funding rate remains high (meaning the market is still waiting for arbitrageurs to enter) or whether the contract's market-making depth is insufficient. Being able to explain the composition of the current spread shows that you truly understand the logic of basis convergence.
