The correlation between #BTC and #ETH is traditionally high, often around 0.9, indicating that the two cryptocurrencies move in tandem. However, since the beginning of 2023, this correlation has experienced periods of decline, particularly after the Shanghai (Shapella) update of #Ethereum : the coefficient over 40 days dropped from 0.95 to 0.82.  These dips can offer opportunities for arbitrage or diversification, as the performances of BTC and ETH occasionally stand out.   Over three months, the correlation remains robust, around 0.94.  In conclusion, while the relationship #BTCETH is generally strong, it can sometimes be flexible, beneficial for active strategies.