As noted elsewhere by a prominent author in the area [25], there is not a widely accepted or consistent definition of the term “bubble”. The GDASF test used here assumes a bubble is any time series interval which deviates from a random walk to become explosive.
While it shares characteristics of both currency and investments, there’s still debate among experts about whether cryptocurrency is clearly one or the other.

Identifying the determinants of asset prices is one of the most important questions in finance. Traditional asset pricing theories are founded on the idea that equity prices should be determined by fundamentals such as earnings (Gordon 1959, Campbell and Shiller 1988). In contrast, the behavioral finance literature posits that prices do not always follow fundamentals due to investor sentiment trading (Shiller 1981, Baker and Wurgler 2006, Stambaugh et al. 2012). Eventually however, equity prices seem to trace their fundamentals (Pa´stor and Veronesi, 2003, 2006, Bartram and Grinblatt 2018).
GURA: Their market cap worldwide is now close to $2.5 trillion, which is almost as large as the GDP of France. Even the big Wall Street banks now trade bitcoin. And Gary Gensler, the head of the Securities and Exchange Commission, shares Warren's concerns. Here's what he said in a recent speech.