Seven of the largest Bitcoin mining pools — Foundry, AntPool, F2Pool, SpiderPool, MARA Foundation, Block Inc., and DMND — joined the Stratum V2 Working Group on May 7, 2026. Combined, these operators represent approximately 75% of global Bitcoin hashrate, currently measured at 998 exahash per sec...
"We are proud to support the wider adoption of Stratum V2. Aligning around an open, interoperable standard allows the industry to collaborate more effectively and drive improvements in efficiency, security and decentralization." — Andy Zhou, CEO of AntPool
Seven of the largest Bitcoin mining pools — Foundry, AntPool, F2Pool, SpiderPool, MARA Foundation, Block Inc., and DMND — joined the Stratum V2 Working Group on May 7, 2026. Combined, these operators represent approximately 75% of global Bitcoin hashrate, currently measured at 998 exahash per second. The move marks the most significant structural change to Bitcoin's block construction process since Stratum V1 became the de facto standard in 2012.
The core change: Stratum V2's Job Declaration sub-protocol allows individual miners — not pool operators — to select which transactions enter new blocks. Under the current V1 regime, four pool operators control transaction selection for roughly 73% of all Bitcoin blocks. The protocol also replaces V1's plaintext communication with end-to-end authenticated encryption, cuts pool bandwidth usage by approximately 60%, and reduces miner bandwidth by 70%. The Stratum V2 Reference Implementation working group projects 40–60% of network hashrate will run V2 by end of 2026.
Bitcoin's mining infrastructure exhibits concentrated control over block template construction. According to CoinDesk data published May 11, 2026, pool-level hashrate distribution stands as follows:
| Pool | Hashrate Share | |------|---------------| | Foundry | 34.2% | | AntPool | 14.2% | | F2Pool | 11.3% | | SpiderPool | 10.5% | | MARA Pool | 4.7% | | Others | ~25.1% |
Foundry and AntPool together control approximately 48.4% of network hashrate. Add F2Pool and SpiderPool, and four entities determine transaction inclusion for roughly 70% of all Bitcoin blocks. Under Stratum V1, pool operators — not the thousands of individual miners contributing compute — build every block template. Miners hash whatever the pool tells them to hash. They have no say in which transactions are selected.
This creates multiple attack vectors. V1 transmits all data in plaintext, exposing miners to hashrate hijacking — where a malicious third party intercepts a miner's connection, modifies the coinbase address, and collects payouts without detection, according to Braiins' security documentation. ISPs, network administrators, and state actors on the network path can monitor mining activity, intercept shares, or redirect hashrate.
In 2023, F2Pool admitted to running a transaction reordering mechanism that prioritized certain transactions for profit, which was removed after community backlash. With the growth of on-chain protocols like Ordinals and Runes creating new fee-extraction opportunities, the incentive for pool-level transaction manipulation has increased.
Stratum V2 was developed in 2019 by Braiins founders Pavel Moravec and Jan Čapek, in collaboration with developer Matt Corallo. The protocol introduces three material changes:
1. Job Declaration Sub-Protocol. Individual miners can construct and submit their own block templates using their own Bitcoin full nodes. The pool validates proof-of-work without dictating transaction selection. This distributes block construction authority across thousands of operators rather than concentrating it in a handful of pool administrators.
2. Authenticated Encryption. V2 implements the Noise Protocol Framework (Noise_NX handshake pattern), replacing V1's plaintext transmission. This eliminates hashrate hijacking, credential exposure, and network surveillance vulnerabilities.
3. Binary Protocol Format. V2 uses a lean binary format instead of V1's JSON-based messaging. This reduces pool bandwidth usage by approximately 60% and miner bandwidth by 70%, according to protocol specifications. Lower latency means faster share submission and better fee capture.
Kenway Wang, CTO of SpiderPool, stated upon joining the working group: "Decentralization is at the core of our mission. Stratum V2 supports it by enabling miner-built templates, while also improving efficiency, particularly for miners in bandwidth-limited environments."
It is important to note what Stratum V2 does not change: hashrate concentration. Foundry will still operate 34.2% of network compute. The protocol shifts control over what goes into blocks without altering who provides the hash power. This distinction matters. Pool operators lose their monopoly on transaction selection, not their role as payout coordinators.
The profitability case for V2 adoption is measurable. According to analysis cited by Crypto Briefing, the protocol can deliver up to 7.4% higher profitability for miners through reduced latency and improved fee capture. In a market where hashprice has fallen to approximately $28–30 per petahash per second per day — a five-year low per the CoinShares Q1 2026 Bitcoin Mining Report — a 7.4% margin improvement is material.
CoinShares' Q1 2026 report found that 15–20% of legacy mining rigs are currently cash-flow negative. At ~$77,000 BTC and ~$30 hashprice, any machine less efficient than a Bitmain S19 XP running on power priced at $0.06/kWh or higher is operating at a loss. The latest-generation Antminer S23 Hydro achieves 9.5 joules per terahash (J/TH), compared to mid-generation rigs at 25–30 J/TH.
For these marginal operators, V2's bandwidth reduction and latency improvements directly translate to lower operating costs and higher effective revenue per hash. Translation proxies already allow V1 firmware to connect to V2 pools without hardware or firmware upgrades, reducing the adoption barrier.
Braiins and Spiral (Block Inc.'s Bitcoin development division) founded the Stratum V2 Working Group in 2022. For four years, it operated as a niche open-source project with limited industry adoption. The May 7, 2026 announcement represents a phase transition.
The projected deployment schedule:
Block Inc.'s presence in the working group is notable. The company manufactures Bitcoin mining hardware, positioning it to embed V2 support at the hardware level. When the ASIC manufacturer, the protocol developer, and the pool operator all align on the same standard, deployment friction decreases substantially.
The transaction selection question carries regulatory weight. Some U.S.-based mining pools have implemented OFAC-compliant transaction filtering, excluding transactions involving sanctioned addresses. Under Stratum V1, this filtering is straightforward: the pool builds the block template, the pool decides what goes in.
Under Stratum V2 with Job Declaration enabled, individual miners construct their own templates. A pool cannot censor transactions it never sees in the template. This architectural change doesn't eliminate regulatory obligations for U.S. operators, but it redistributes the locus of compliance from pool to miner.
The timing is notable. The GENIUS Act, signed into law in July 2025, brought payment stablecoins under the Bank Secrecy Act with comprehensive AML and sanctions compliance requirements. As regulatory frameworks expand into on-chain activity, the question of who bears compliance responsibility for block-level transaction inclusion becomes increasingly relevant.
According to analysis by The Block, even if the entire U.S. mining industry implemented block-level OFAC compliance, Bitcoin would continue to settle sanctioned transactions because mining is globally distributed. Stratum V2 further complicates centralized compliance by distributing template construction across individual miners worldwide.
Stratum V2 is not the only protocol addressing block construction centralization. OCEAN, the mining pool founded by Bitcoin Core developer Luke Dashjr and backed by a $6.2 million seed round from Jack Dorsey, launched its DATUM protocol as an alternative approach.
The architectural distinction is meaningful. Under Stratum V2's Job Declaration, the pool can theoretically reject a miner's template during the negotiation phase, as the pool sees the full transaction list. Under DATUM, the pool receives only merkle branches — it is cryptographically blind to template contents, making censorship architecturally impossible rather than policy-dependent.
OCEAN commands approximately 2% of global hashrate as of early 2026 — a fraction of the V2 coalition's 75%. The practical question is whether DATUM's stronger censorship-resistance guarantees outweigh V2's broader industry adoption. From an economic-value perspective, the answer likely depends on whether miners value provable censorship resistance enough to accept a smaller pool's variance and payout structure.
The April 2024 halving cut Bitcoin's block subsidy from 6.25 to 3.125 BTC. The resulting economics have been punishing for miners. Hashprice peaked at approximately $63/PH/s/day in July 2025 before falling to the $28–30 range by Q1 2026 — a decline of over 50% in nine months.
Network difficulty has continued to rise, from 132.47T to 135.64T in mid-May 2026, while hashrate approaches 1,000 EH/s. The CoinShares report projects 1.8 zetahash by year-end 2026. More hashrate competing for a fixed block subsidy compresses margins further.
In this environment, the 7.4% profitability improvement from V2 adoption is not abstract — it determines which operations survive. The top three mining countries (U.S., China, Russia) control approximately 68% of global hashrate, per CoinShares. Emerging markets including Paraguay, Ethiopia, and Oman have entered the global top 10, driven by low energy costs. For bandwidth-constrained miners in these regions, V2's 70% bandwidth reduction is particularly significant.
Simultaneously, publicly traded mining companies have signed over $70 billion in GPU co-location and cloud service deals with hyperscalers, pivoting toward AI infrastructure as mining margins compress. This migration reduces the pool of dedicated Bitcoin miners, potentially increasing the relative influence of remaining mining pools over block construction — making the V2 decentralization shift more urgent.
The Stratum V2 adoption by 75% of Bitcoin's hashrate operators does not solve mining centralization. It changes who decides what goes into blocks — a distinction that matters more than hashrate distribution for Bitcoin's censorship resistance properties. The economic value captured at the mining layer — currently compressed to five-year lows at $28–30 hashprice — now flows through a protocol that encrypts communication, reduces bandwidth costs, and allows individual miners to participate in block construction for the first time at scale.
Whether V2 delivers on its decentralization promise depends on adoption of the Job Declaration sub-protocol specifically. Pools joining the working group signals intent, not implementation. The 40–60% deployment target by year-end 2026 is a projection, not a commitment. The gap between joining a working group and shipping production-ready Job Declaration support to thousands of heterogeneous mining operations is substantial.
The data is clear on one point: at current hashprices, miners need every efficiency gain available. The 7.4% profitability improvement, the bandwidth reductions, and the encryption are immediate, tangible benefits regardless of the decentralization outcome. That economic self-interest — not ideological commitment to censorship resistance — is what will drive V2 adoption.