Culper Research has initiated a short position against ether (ETH) and related stocks, including BitMine (BMNR), citing concerns over Ethereum's economic health post its December 2025 Fusaka upgrade. The firm argues that the upgrade has flooded the network with excess blockspace, leading to a sharp decline in transaction fees and staking yields, potentially triggering a negative feedback loop that could undermine network security. The report also notes that Ethereum co-founder Vitalik Buterin sold nearly 20,000 ETH this year, worth approximately $40 million, suggesting a lack of confidence in the network's current trajectory. Culper challenges bullish claims from BitMine's chairman, Tom Lee, regarding network activity, attributing the rise in transaction counts to address poisoning attacks. Additionally, Culper highlights BitMine's significant unrealized losses, with its ether holdings estimated to be 45% underwater.