Japan Open Chain to Begin Testnet Migration for the "Tokyo Hardfork" on September 7
～Migrating to a Consensus Mechanism Nearly Identical to Ethereum's PoS to Greatly Improve Compatibility, Strengthening Governance through On-Chain Validator Management. Mainnet Migration Planned for November～
Japan Blockchain Foundation, Co., Ltd. (Representative: Daimei Inaba), the operator and administrator of the consortium behind Japan Open Chain (JOC), a fully Ethereum-compatible public blockchain operated by Japanese enterprises, is pleased to announce that it will carry out a testnet hardfork for the "Tokyo Hardfork" — the largest protocol upgrade since the network's launch — on September 7, 2026. After confirming that the testnet verification results present no issues, the Company plans to carry out Phase 1, "The Merge," on the mainnet in November 2026.
The Tokyo Hardfork is an upgrade that fully migrates JOC's consensus mechanism from PoA (Proof of Authority) to PoSA (Proof-of-Stake Authority). PoSA is a model that combines a PoS (Proof of Stake) consensus layer structurally identical to the Ethereum mainnet with an authority layer in which the consortium manages validator participation.
This upgrade carries two major implications. First, JOC's consensus method will become nearly identical to Ethereum's PoS, greatly improving compatibility with the Ethereum ecosystem. Second, validator management will be moved on-chain via smart contracts, significantly strengthening the transparency and verifiability of network governance.
Under this upgrade, all existing chain data and transaction history will be fully preserved, and the Chain ID (84) will not change. No action is required from DApps, services, or wallets connecting to JOC via an RPC endpoint, nor from general users. However, node operators who sync directly from the boot node to run their own independent node will need to take action in advance (details below).
◽️ Background
Since the network's launch, JOC has adopted the PoA model to achieve rigorous consensus formation among highly trusted domestic companies, providing a stable blockchain foundation. However, as the network matured and its ecosystem expanded, the current PoA model has faced the following challenges:
- Approval of new validators relies on mechanisms within the client software, making transparent on-chain management and auditing difficult
- As Ethereum has migrated to PoS, it has become harder for JOC to keep pace with subsequent protocol evolution
- JOC has been unable to realize a standard validator operating model based on economic incentives
Entering 2026, as blockchain adoption in the financial sector — including stablecoins and security tokens — accelerates, such use cases require high-frequency, highly reliable network operation together with long-term, transparent governance. By migrating to PoSA along the same upgrade path Ethereum completed with "The Merge" in 2022, the Company will fundamentally resolve these challenges and build the foundation for next-generation financial infrastructure.
◽️ Features of the Tokyo Hardfork
1. A method nearly identical to Ethereum's PoS, greatly improving compatibility
With the Tokyo Hardfork, JOC's consensus method will become nearly identical in specification to the PoS that the Ethereum mainnet has adopted since "The Merge" in 2022. JOC has long been a fully Ethereum-compatible (EVM-compatible) chain, providing smart contract and wallet compatibility; with this upgrade, JOC will share the same specification with Ethereum not only at the application layer but also at the consensus layer.
This is expected to bring the following benefits:
- Node implementations, development tools, and monitoring/auditing tools standard in the Ethereum ecosystem can be used as-is. Like Ethereum, JOC's validator nodes will be configured with a combination of an Execution Client (Geth) and a Consensus Client (Lighthouse, etc.).
- Ethereum's validator operation know-how, talent, and tooling can be directly repurposed, greatly reducing the operational burden and learning cost for companies participating as validators.
- Because the specification becomes nearly identical to Ethereum's, JOC will be able to quickly follow future Ethereum protocol upgrades. As part of the Tokyo Hardfork, JOC will sequentially apply the same Shapella, Dencun, and Pectra upgrades that Ethereum has undergone.
As a public chain originating from Japan, establishing a structure that can continuously incorporate the technological evolution of Ethereum — which has the world's largest developer community — is an essential foundation for becoming financial infrastructure used over the long term.
2. Strengthened on-chain governance through smart-contract validator management
Under the current PoA model, the list of validators authorized to produce blocks is managed as a client software configuration, and adding or removing validators depends on software-level procedures. After the Tokyo Hardfork, this management will be executed on-chain via smart contracts.
- Validator registration, addition, and forced removal will be executed when the consortium owner calls the contract through a multisig wallet, with every action recorded on-chain as a transaction.
- Because stake deposits and the distribution and withdrawal of rewards are also processed through the contract, any third party can verify on-chain who the validators are and how they joined or left.
- The scope of decisions made by the operating entity and the scope automatically executed by the protocol are clearly separated. Both Penalty (reward deduction) for failure to fulfill obligations and Slashing (partial burning of staked principal) for provable malicious acts such as double-signing are automatically applied at the protocol level without any intervention by the operating entity.
For a consortium-type chain co-operated by multiple companies, how to ensure operational transparency is an important consideration for businesses evaluating long-term use. The Tokyo Hardfork addresses this challenge head-on by moving validator management — the foundation of network operations — to an on-chain, verifiable mechanism.
3. Validator operation based on economic incentives
Validators register with a stake of 32 JOC and earn rewards by fulfilling two roles: Block Proposal and Attestation. This transitions the network to a standard PoS operating model in which economic incentives work to support stable network operation.
4. Phased rollout across four phases
To avoid downtime, the new consensus layer (beacon chain) will run in parallel with the existing network, and the migration will be rolled out in the same four phases that Ethereum went through.
| Phase | Name | Key Changes |
|---|---|---|
| Phase 1 | The Merge | Halting PoA, start of PoS block production |
| Phase 2 | Shanghai-Capella (Shapella) | Enables withdrawal of staking rewards |
| Phase 3 | Cancun-Deneb (Dencun) | Network throughput optimization |
| Phase 4 | Prague-Electra (Pectra) | Advanced validator management, implementation of forced removal |
◽️ Implementation Schedule
| Timing | Details |
|---|---|
| September 7, 2026 | Testnet hardfork implementation (verification of all 4 phases) |
| September–October 2026 | Node migration work by each validator company |
| November 2026 (planned) | Mainnet Phase 1, "The Merge" |
| December 2026 (planned) | Mainnet Phase 2, "Shapella" |
| January 2027 (planned) | Mainnet Phase 3, "Dencun" |
| February 2027 (planned) | Mainnet Phase 4, "Pectra" |
On the testnet, the Company will build a verification environment equivalent to production and apply all four phases using the same procedures as production to confirm operation. The mainnet implementation schedule will be finalized based on the testnet verification results. Please note that the mainnet implementation date has not yet been confirmed. Once details are finalized, they will be announced separately, approximately two weeks before implementation.
◽️ For Current JOC Users
Under this hardfork, the RPC endpoint, Chain ID (84), contract addresses, and transaction history will all be preserved without change or loss. The action required differs depending on how you use JOC, so please check the details below.
■ If you connect via the RPC endpoint — No action is required
DApps, services, and wallets connecting through JOC's RPC endpoint require no action before or after the hardfork. You can continue using the same endpoint and the same methods as before.
■ If you run your own node syncing directly from the boot node — Prior action is required
If you have built your own node and sync directly to the network via the boot node, prior action and a change to your node configuration are required. With the migration to PoSA, in addition to the existing standalone Execution Client (Geth) configuration, you will need to newly run a Consensus Client.
If action is not taken by the deadline, the affected node will be unable to receive new blocks after the hardfork and will lose synchronization with the network. As a result, applications and wallets connected to that node will be unable to obtain the latest block information and transactions, impacting service.
The Company will individually guide applicable partner companies through the necessary procedures and migration steps. Businesses who believe they may be affected should contact the inquiry desk below by around September 2026.
Technical documentation: https://www.japanopenchain.org/en/docs/developer/connect-joc/mainnet/
◽️ Future Outlook
Following the completion of the Tokyo Hardfork (JOC v2), the Company plans to begin work on its next upgrade, the "Osaka Hardfork (JOC v3)." The Osaka Hardfork will introduce a multi-tier validator concept that allows up to 500 standard validators to participate alongside the 21 core validators, further enhancing the network's decentralization and fault tolerance through participation from both Japan and abroad. By limiting core validators — those able to take part in major votes — to Japanese companies, Japan's political and economic stability will continue to contribute to the chain's governance.
The Company will continue to promote the construction of next-generation digital financial infrastructure that enterprises, financial institutions, and local governments can use with confidence, through both regulatory frameworks and technological innovation.
◽️ Reference
About "PoSA (Proof-of-Stake Authority)"
PoSA is a consensus model that combines a PoS consensus layer structurally identical to Ethereum's post-"The Merge" design with a consortium-managed authority layer that controls who can become a validator. Its distinguishing feature is that it maintains the transparency and verifiability of a public chain while limiting the entities that operate the network to a group of trusted companies. On JOC, the consortium owner is responsible for validator registration and stake deposits, and the Company will initially operate this role.
About "Japan Open Chain"
Japan Open Chain is a practical, Ethereum-compatible (Layer 1) public blockchain operated by Japanese companies. Together with leading industry giants and Web3 innovators, it aims to provide a secure, high-speed, and low-cost blockchain infrastructure accessible to users worldwide. This project seeks to revolutionize global digital finance by building future financial infrastructure through initiatives like bank-led stablecoin projects and the digitization of assets such as NFTs.
The blockchain is currently operated by validators (blockchain operation partners) including Dentsu Inc.; insprout Corporation; Kudasai Co., Ltd.; pixiv Inc.; Kyoto University of the Arts; Hatena Co., Ltd.; CAC Corporation; CYBERLINKS CO.,LTD.; G.U.Technologies, Inc.; and others. The blockchain is managed in a decentralized manner and is expected to expand to 21 validators in the future.
◽️ About Japan Blockchain Foundation Co., Ltd.
Japan Blockchain Foundation Co., Ltd. operates and manages the consortium for "Japan Open Chain," an enterprise-oriented public blockchain co-operated by trusted Japanese companies in compliance with Japanese law. Through infrastructure development that emphasizes governance design and regulatory compliance, the company promotes the social implementation of next-generation financial infrastructure, including stablecoin and token utilization by financial institutions, enterprises, and local governments.
[ Company Overview ]
Company Name ：Japan Blockchain Foundation Co., Ltd.
Location ：Cerulean Tower 15F, 26-1 Sakuragaoka-cho, Shibuya-ku, Tokyo, Japan
Representative ：Representative, Daimei Inaba
Founded ：April, 2018
URL ：https://www.jbfd.org/en/
Business Overview ：Operation and Management of Web3 Infrastructure
◽️ For Inquiries Regarding This Press Release
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Japan Blockchain Foundation Co., Ltd. - Public Relations
Inquiry Form: https://www.japanopenchain.org/en/contact
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