Seven mining pools controlling approximately 75% of Bitcoin's global hashrate joined the Stratum V2 Working Group on May 7, 2026. The signatories — AntPool, Foundry, F2Pool, SpiderPool, Block Inc., MARA Foundation, and DMND — committed to adopting a protocol that shifts block template constructio...
"We are proud to support the broader adoption of Stratum V2. Aligning around an open, interoperable standard lets the industry collaborate on efficiency, security, and decentralization." — Andy Zhou, CEO, AntPool
Seven mining pools controlling approximately 75% of Bitcoin's global hashrate joined the Stratum V2 Working Group on May 7, 2026. The signatories — AntPool, Foundry, F2Pool, SpiderPool, Block Inc., MARA Foundation, and DMND — committed to adopting a protocol that shifts block template construction from pool operators to individual miners. The move addresses a structural centralization risk that has concentrated transaction selection authority in fewer than five entities for more than two years.
Under the current Stratum V1 standard, deployed since 2012, pool operators unilaterally determine which transactions enter new blocks. Foundry alone controls 33.6% of network hashrate; AntPool holds 17.9%. Together, the two pools produce roughly half of all Bitcoin blocks. The Stratum V2 protocol's job negotiation sub-protocol allows miners running their own full nodes to construct block templates independently, decoupling the economic function of pools — aggregating hashrate and distributing rewards — from the censorship-sensitive function of deciding block contents.
The timing is notable. Network difficulty reached 132.47 trillion in early May 2026, with hashrate approaching 998 exahash per second. An estimated 20% of miners operate at a loss, per CoinShares data. Stratum V2 offers potential profitability gains of up to 7.4% through lower latency and improved fee capture, giving margin-pressured operators a financial incentive alongside the decentralization argument.
Marek "Slush" Palatinus introduced the Stratum V1 protocol in 2012 as a replacement for the obsolete getwork protocol. At the time, Bitcoin's total network hashrate measured approximately 20 TH/s. The protocol standardized communication between miners and pools, enabling the pooled mining model that now dominates the network.
Fourteen years later, network hashrate has grown roughly 50 million-fold to approximately 998 EH/s. The protocol has not kept pace. Under V1, the pool operator runs a full Bitcoin node, examines the mempool, selects transactions, constructs the final block template, and distributes work units to connected miners. Miners perform proof-of-work computation on templates they did not build and cannot modify.
The result is extreme concentration of block construction authority:
| Pool | Hashrate Share | Blocks/Day (approx.) | |------|---------------|----------------------| | Foundry USA | 33.6% | ~48 | | AntPool | 17.9% | ~26 | | F2Pool | 11.3% | ~16 | | SpiderPool | 10.5% | ~15 | | MARA Pool | 4.7% | ~7 | | Top 5 Total | 78.0% | ~112 |
Source: Hashrate Index, May 2026.
Foundry and AntPool together exceed the 51% threshold that Bitcoin's security model treats as critical. While pool operators are not monolithic entities — miners can switch pools — the structural arrangement means that transaction inclusion policy for the majority of Bitcoin blocks is set by a handful of corporate operators. Proxy pooling further obscures the picture: some ostensibly independent pools route hashrate through larger operators, making actual concentration higher than block production data suggests.
Geographic risk compounds the issue. Foundry's miners are heavily concentrated in the United States, meaning regional grid failures, severe weather, or regulatory actions could produce network-wide disruptions.
Stratum V2 was developed by Braiins (Jan Čapek and Pavel Moravec) in collaboration with Matt Corallo. The protocol introduces three core improvements over V1:
1. Job Negotiation Sub-Protocol. The central feature. A miner running a Bitcoin full node constructs its own block template — selecting transactions from its own mempool based on its own criteria — and proposes that template to the pool. The pool validates the template and assigns work. This decouples reward distribution from transaction selection.
2. Encrypted Communication. V1 transmits all data in plaintext, leaving mining traffic vulnerable to man-in-the-middle attacks and hashrate hijacking. V2 introduces authenticated encryption using the Noise Protocol Framework.
3. Reduced Bandwidth. V2 uses a binary encoding format that reduces data transmission overhead compared to V1's JSON-based messaging. The protocol claims bandwidth reductions of up to 50%, which translates to lower latency and faster share submission.
The job negotiation feature is the most consequential. Under V1, compromising five pool operators would theoretically grant control over transaction inclusion in approximately 78% of all blocks. Under V2 with widespread job negotiation deployment, an attacker would need to compromise thousands of individual miners running their own nodes — a qualitatively different and far more difficult attack surface.
The protocol does not eliminate pools. It preserves the economic aggregation function — variance reduction through pooled rewards — while redistributing the censorship-sensitive function to individual participants.
The Stratum V2 Working Group was founded in 2022 by Braiins and Spiral, Block Inc.'s Bitcoin technology arm. For four years, it operated as an independent open-source community with limited industry adoption.
The May 7, 2026 announcement marked a phase shift. Seven pools joined simultaneously:
The Stratum V2 Working Group stated that "by maintaining Stratum V2 as a public, vendor-neutral specification, we remove compatibility barriers and allow the ecosystem to focus on what matters most."
Prior to this expansion, adoption was limited. Braiins Pool offered full Stratum V2 support including job negotiation. DMND launched as the first V2-native pool. The addition of the seven largest commercial pools transforms V2 from a niche option into a potential industry standard.
However, joining a working group is not the same as deploying the protocol. None of the seven new members have announced production deployment timelines. The commitment is to participate in protocol development and testing, not to immediately migrate existing infrastructure.
The decentralization argument alone may not drive adoption. The economic argument might.
Bitcoin mining economics in May 2026 are constrained. The April 2024 halving reduced the block subsidy from 6.25 BTC to 3.125 BTC. At approximately $80,000 per BTC, the daily subsidy across the network totals roughly $36 million (450 BTC × ~$80,000). Transaction fees add variable revenue, but the subsidy remains dominant.
Key metrics as of mid-May 2026:
| Metric | Value | |--------|-------| | Network Hashrate | ~998 EH/s | | Mining Difficulty | 132.47 T (rising to ~136.33 T) | | Hashprice | $36–$38 per PH/s per day | | Block Subsidy | 3.125 BTC (~$250,000) | | Miners Operating at Loss | ~20% (CoinShares est.) | | Breakeven Electricity Cost | $0.06–$0.08/kWh |
Stratum V2 claims profitability improvements of up to 7.4% through two mechanisms: reduced latency in share submission (binary encoding and encrypted channels reduce round-trip overhead) and improved fee capture through miner-constructed templates that can optimize transaction selection for maximum fee revenue rather than relying on pool-level heuristics.
For a mining operation at the margin — hashprice of $37/PH/s/day against breakeven costs — a 7.4% revenue improvement represents the difference between viability and shutdown. This financial incentive may prove more persuasive than abstract decentralization concerns, particularly for industrial operators whose primary obligation is to shareholders.
CoinShares forecasts network hashrate rebounding to 1.8 ZH/s (1,800 EH/s) by year-end 2026, despite some hashrate departing for AI compute applications. If accurate, competitive pressure will intensify further, strengthening the economic case for protocol-level efficiency gains.
The concentration of block template construction in a small number of corporate entities creates a regulatory pressure point. U.S.-based Foundry, operating under American jurisdiction, is subject to OFAC sanctions compliance. If regulators directed Foundry to exclude specific transactions or addresses from block templates, a single order could affect one-third of all Bitcoin blocks.
This is not theoretical. Analysis of Bitcoin block contents has periodically identified patterns consistent with OFAC-compliant transaction filtering by major pools, though conclusive attribution is difficult.
Stratum V2 with job negotiation distributes this vulnerability. If individual miners construct their own templates, no single jurisdictional action can systematically filter transactions from the majority of blocks. An OFAC-sanctioned transaction excluded by a U.S.-based miner's template would still be included by miners operating in other jurisdictions, maintaining the network's censorship resistance properties.
The regulatory calculus cuts both ways. Regulators may view Stratum V2's diffusion of block construction authority as an obstacle to enforcement. Pool operators may face pressure not to adopt job negotiation features. The working group's emphasis on V2 as a "vendor-neutral specification" may be partly strategic — framing the protocol as an industry efficiency standard rather than an anti-regulatory tool.
The Stratum V2 Reference Implementation (SRI) working group projects that by end of 2026, V2 will be the default protocol for new ASIC firmware shipments. If achieved, the protocol could reach 40–60% of network hashrate within 12–18 months of firmware deployment.
Several barriers remain:
Firmware Dependencies. Most ASIC miners ship with V1 firmware. Adopting V2 requires firmware updates or replacement. Older hardware may not receive updates, creating a multi-year transition window.
Full Node Requirements. Job negotiation requires miners to run their own Bitcoin full nodes. Many small-scale miners rely on pool-provided block templates precisely because running a full node requires additional hardware, bandwidth, and technical expertise.
Pool Revenue Models. Pool operators currently extract value from block template construction — including MEV-adjacent strategies and priority transaction ordering. Ceding template construction to miners reduces pool operators' revenue optimization options. This creates a misaligned incentive: pools are committing to a protocol that diminishes their own competitive advantages.
Testing and Validation. Production deployment at the scale of Foundry (33.6% of hashrate) requires extensive testing. A protocol bug affecting block template construction at that scale could destabilize the network.
The Stratum V2 working group expansion represents the most significant structural commitment to mining decentralization since the protocol's original conception. The numbers are clear: 75% of hashrate backing an open standard that redistributes block construction authority. The economic incentives — margin improvement for cost-pressured operators — align with the decentralization objectives in a way that pure ideological arguments historically have not.
The gap between commitment and deployment remains wide. Joining a working group is a statement of intent, not a production milestone. The protocol must navigate firmware upgrade cycles, full node adoption curves, and the structural resistance of pool operators whose current business models benefit from centralized template construction.
What the data shows is a mining industry that recognizes its concentration problem and has taken a first coordinated step toward addressing it. Whether that step translates into meaningful decentralization of block construction authority depends on implementation timelines that remain unannounced. The protocol is sound. The commitments are public. The deployment is yet to come.