Expectations for bitcoin's (BTC) price over the next six months have turned positive after a long time, in another sign of confidence in the cryptocurrency's latest bull revival.

Bitcoin's 180-day call-put skew has crossed above zero for the first time since the start of 2021, indicating that bullish call options expiring in six months have become pricier than bearish put options, according to chart sourced from digital assets data provider Amberdata.

The skew measures the price for calls relative to puts and is a good measure of the consensus for six months ahead, as both institutions and retail investors use options to speculate and hedge against future shifts in the price of the cryptocurrency.

"This is a measure of market sentiment and flows, because it encapsulates what people are willing to pay to acquire an asymmetric payout on either the upward or downward direction of the market," Deribit, the largest crypto options exchange per trading volumes and open interest, said in an explainer.

Options are derivative contracts that give purchasers the right but not the obligation to buy or sell the underlying asset at a predefined price on or before a specific date. A call option gives the right to buy, while the put offers the right to sell.

Both short-term and long-term call-put skews have turned positive, the first such instance since 2021.

The demand for bullish calls tied to bitcoin picked up last week as the cryptocurrency's price topped its 200-day moving average for the first time since April. The cryptocurrency ended last week with a 21.9% gain, the biggest percentage rise since February 2021.

"Calls [at] $18,000/$19,000 bought with the spot at $17,000 were the main trades," Amberdata's Gregoire Magadini wrote in the weekly newsletter published Sunday, while taking note of the positive skews.

"The flow of options can give insight on the technical levels of support and resistance observed by market participants. In this regard, note the February purchases of $22,000/$24,000 [strike] calls at the break of $19,000," Magadini added.

The bullish sentiment is also evident from the renewed premium in bitcoin futures listed on the Chicago Mercantile Exchange (CME). The front-month contract expiring on Jan. 28 gapped higher early Monday to hit a four-month high of $21,535 as the cryptocurrency's spot market price rose to $21,437, the level last seen in late October.

The positive turnaround is consistent with the recent improvement in the macroeconomic backdrop and risk revival in traditional markets. Besides, the cryptocurrency tends to gain ground in months leading up to the mining reward halving, a programmed code aimed at reducing the pace of supply expansion by 50% every four years. Bitcoin's fourth halving is due sometime in March 2024.