Bitcoin options are biased towards bullish, 25 Delta skew turns negative

Bitcoin options tilt in the bullish direction, and the 25-delta skewness turns negative.

As the momentum of the spot market cools, the focus of bitcoin options trading gradually shifts towards calls. According to Glassnode data, the market has a negative skew. This pricing change suggests that upside exposure is relatively more expensive, but it does not mean that new call option buying volume has been generated.

Key Data and Background

According to CryptoSlate citing Glassnode data, Bitcoin's 25-delta skewness has turned from positive to negative. Glassnode's September 8, 2026 update included a chart of "Option Delta Skewness" confirming that the metric was already in negative territory. Specifically, Bitcoin 25-delta option skewness decreased from +0.79% to-2.05%.

According to the reported methodology, negative skewness indicates that call options become more expensive relative to puts; this does not equate to the actual call purchase volume that occurs. In addition, the term structure of the option and the exact comparison window remain unidentified.

Summary of core points

• Glassnode's chart shows negative option skewness.
• Under the convention of "puts minus calls", negative skewness means that call options are relatively higher;CryptoSlate interprets this observation in a bullish manner.
• The reported changes in skewness alone cannot establish net call option buying behavior or predict the upcoming rise of Bitcoin.

Interpretation: The meaning behind the shift to negative skewness

What does the report data reveal?

CryptoSlate's comparison of skewness describes changes in relative option pricing, rather than actual measurement of call option purchases. Existing evidence does not identify the buying volume of exercised call options or the net new call positions, so "call options are more popular" remains at the pricing observation level.

How to measure 25-delta skewness?

25-delta skewness compares the implied volatility of comparable call and put options with the same expiration date and matching the absolute Delta value of the put option. When a call option has a high implied volatility, the result of "put implied volatility minus call implied volatility" will become negative; otherwise, the sign will reverse.

CryptoSlate provides a symbolic explanation that favors bullish, but the main readable evidence does not identify formulas, terms, sample exchanges, or comparison endpoints. Missing expiration date details are crucial to comparing this signal to the expiration coverage of Bitcoin and Ethereum options.

What does the bullish bias imply for Bitcoin sentiment?

Why more expensive call options may imply upside interest:

The reported negative bias is consistent with interest in upper exercise gains, although cheaper puts may also lead to changes in spreads. However, it could not identify who initiated the trade or whether the positions expressed directional views, hedges or spread strategies.

According to CryptoSlate, in the latest report's weekly observation, net inflows of U.S. spot Bitcoin ETFs reached $681.2 million, compared with $247.8 million previously (no exact time window provided). These aggregate flows provide background information on the inflow coverage of the iShares Bitcoin Trust Fund, but do not identify the participants behind option repricing.

Why negative skewness does not guarantee an increase:

According to CryptoSlate, the cumulative spot volume spread (CVD) is still negative at-29.6 million US dollars, up from-84.9 million US dollars previously. Despite the improvement, sell-initiated volume is still higher than buyer-initiated volume in the reported metrics; its exact aggregation window has not yet been specified.

This negative spot CVD situation complicates the interpretation of calls from options. Glassnote describes increased capital inflows, rising ETF demand and futures leverage build-up, while spot momentum cools; its reference to negative volatility spreads involves a separate indicator.

Market Status and Outlook

After a flat week, Bitcoin prices held steady around $79,100. Capital inflows, ETF demand and futures leverage are all accumulating, while cooling spot momentum and deeply negative volatility spreads keep the market in a fine balance.

How to confirm a larger shift to Bitcoin call options?

1. Examine persistence across expiration dates: Reported negative skewness endpoints need to be extended over comparable observations and different expiration dates before supporting broader conclusions. Existing evidence does not establish continuity across expiration dates.
2. Compare pricing to trading activity: To verify reported changes in skewness, look at the volume of call and put options, changes in open interest, signed trading flow, and overall implied volatility and spot prices. Trading volume and open interest alone cannot distinguish between buying and selling.

Over the next trading day, please pay close attention to ETF flow updates and whether spot selling eases, as well as the price reaction surrounding the US$79,100 reference level cited by Glassnode. This would link option signals to Bitcoin's price response to stronger ETF purchases; the reference level is historical observation only and not a proven support or resistance level.

Disclaimer : This article is for information purposes only and does not constitute financial or investment advice. There are significant risks in the cryptocurrency and digital asset markets. Be sure to conduct independent research before making a decision.