With transaction demand drying up and fee income plunging, experts warn Bitcoin faces a sustainability crisis despite its price hitting all-time highs.

Bitcoin mempool activity has hit an all-time low, miners’ fee revenue has declined, and some in the crypto community are sounding alarms about the world’s most valuable blockchain’s long-term sustainability.

According to data from Blockchain.com, just a few thousand unconfirmed transactions remain in Bitcoin’s mempool as of press time, down from hundreds of thousands during peak periods like the post-halving Rune mint frenzy. Fee revenue now accounts for less than 0.5% of miner income, far below levels seen in previous bull markets.

“Simply put, almost all of Bitcoin's actual users have gone away. At all-time price highs, too,” wrote Joel Valenzuela, Business Development lead at Dash, in an X post. “We're facing a major crisis. Either the Bitcoin network goes bankrupt, undergoes major changes, or the asset becomes a completely custodial asset run by governments and institutions.”

The mempool — the queue of pending Bitcoin transactions — acts as a buffer when transaction demand exceeds block capacity. Users attach fees to incentivize miners to include their transactions in the next block. When activity surges, so do fees. But when the mempool is clear, competition for blockspace disappears, and so does miner revenue from fees.

Miners Face Declining Revenue

With the mempool empty, miners are already feeling the squeeze. Ethan Vera, chief operating officer at Luxor Technologies, a Bitcoin mining infrastructure provider, told The Defiant that Bitcoin’s long-term security model hinges on either fee growth or sustained price appreciation.

“We believe that continued investment in infrastructure and hashrate production is a key element of Bitcoin's security,” Vera said, adding that “as block rewards decrease, it is critical that Bitcoin price increases and/or transaction fees increase...”

“So while low transaction fees are not a cause of concern in the near term, they are really important in the mid to long-term, and miners should be encouraging more projects to consume blockspace and transact on the L1,” Vera explained.

Others point to changing patterns in both user behavior and protocol usage. For instance, as doggfather, CEO of Doggfather Analytics, explained in a commentary for The Defiant, retail investors are just “not there yet or they don't come at all during this cycle because retail rather invests in ETFs and similar indirect vehicles (like exchange-traded notes in other legislations).”

Network Security at Stake

Another factor behind the mempool emptiness is the lack of non-financial transaction activity. With the minting of Ordinals and fungible tokens like BRC-20s and Runes now largely dormant, blockspace demand has plummeted, doggfather noted.

“The mempool was crowded and fees were high when there were ‘hot’ ordinals or rune mints. The most famous block was after the fourth halving at block 840,000. The fees were 37.626 BTC ($2,402,245) just for this one block. Everyone wanted to get their Rune ticker first and paid extreme fees,” he said.

But concerns run deeper than usage. “Fee revenue for miners is now a pitiful fraction of a percent, endangering security,” said Nishant Sharma, head of developer ecosystem at Doma Protocol. “Worse, mining’s centralized, with the top five pools, including Foundry and AntPool, controlling over 60% of blocks.”

Sharma highlighted grassroots mining efforts as a potential way to challenge centralization. He described a new mining pool model that charges no fees to participating miners, offers Lightning Network payouts, and is designed to empower smaller, home-based miners to compete with dominant pools.