MARA Pool.

MARA Pool belongs to MARA Holdings, a bitcoin mining company listed on Nasdaq that describes itself as one of the world’s largest; it was called Marathon Digital Holdings until August 2024. Fred Thiel, its chief executive, said in May 2021 that most of Bitcoin’s mining power was “concentrated in pools in a single country outside the United States”, and that “by shifting mining power back to North America” the network would become more decentralised. The pool found its first block, 682,170, on 6 May 2021. Other mining companies used it from September 2021 until May 2022; since then it has mined only with MARA’s own machines, which made it, in the words of 0xB10C, a developer who studies mining poolsMining poolA group of miners who share the work of finding blocks and split the rewards, so each gets paid steadily instead of rarely., “the only private pool in the top five” in 2025.

It began as the “Marathon OFAC Pool”, built with software licensed from DMG BlockchainBlockchainBitcoin's shared record of every payment since 2009, stored in blocks that each link to the one before — which is what makes it a chain. to leave out transactions from people on the US Treasury’s sanctions list, which its Office of Foreign Assets Control (OFAC) keeps. Leaving them out, Thiel said, meant the bitcoin MARA produced would be “‘clean’, ethical, and compliant with regulatory standards”, which he said large funds were asking for. Its first blocks were tagged “OFAC Compliant Block”. Many in the industry saw the pool as a threat to Bitcoin’s promise that nobody can censor a transaction, The Block reported, and after that backlash MARA said on 31 May 2021 that the pool “will no longer filter transactions” and would run the standard Bitcoin Core software, ready for TaprootTaprootA 2021 upgrade that added Schnorr signatures and addresses starting bc1p, making complex payments cheaper and more private..

Thiel said MARA was “committed to the core tenets of the Bitcoin community, including decentralization, inclusion, and no censorship”, though he told The Block there was “a certain amount of Bitcoin politics involved here”, and that the industry “will have to be responsive to regulatory requirements” if investors were to take part. The tag was gone from its blocks by 8 June. In its 25 days of filtering, 0xB10C saw the pool neither leave out nor include a sanctioned transaction, probably because such transactions were rare.

Each MARA Pool block’s first transaction pays the whole reward to a single MARA address. That reward is separate from the transactions the block confirms, which MARA picks with its own software. In September 2023 an experimental version of that software cost it a block: block 809,478 placed some transactions before the ones they spent from, so the rest of the network rejected it and MARA lost a reward of about 6.44 bitcoin, 0xB10C reported. MARA said it had been experimenting with “a small portion of our hash rateHashrateHow many guesses a second all of Bitcoin's miners make together. More hashrate makes the network harder to attack.” and that the error came from “an unanticipated bug”. Since July 2024 the pool has also mined transactions that people pay mempool.space’s Accelerator to speed up, as one of the service’s first five partner pools.

Running its own pool lets MARA confirm transactions that follow Bitcoin’s rules but that most nodes won’t pass on, because they are very large or unusual. In January 2023 it mined 16 of them for RSK, a sidechainSidechainA separate blockchain that bitcoin can move to and back from, trading Bitcoin's rules for different features or speed. whose bridge to Bitcoin had more than 3,000 bitcoin stuck in a script of this kind, 0xB10C found.

In February 2024 MARA launched Slipstream, a service for sending such transactions straight to MARA. A transaction sent this way isn’t shared with the rest of the network until it is in a block, so only MARA Pool can confirm it, and MARA doesn’t promise to. On 3 August 2026 MARA opened Slipstream to anyone, days after researchers disclosed a flaw in how Coldcard hardware walletsHardware walletA small device that holds your private keys and signs payments inside itself, so the keys never touch your internet-connected computer or phone. made their keys, Bitcoin.com reported, as owners raced to move their coins. Sending privately meant thieves who could guess those keys never saw the transaction, so they couldn’t use replace-by-feeReplace-by-fee (RBF)A way to replace an unconfirmed payment with a conflicting version that pays a higher fee. Only one can remain in the same valid chain. to swap in one of their own.