Polkadot's JAM: Redefining Blockchain Architecture with RISC-V

In April 2025, Vitalik Buterin proposed something that would have seemed heretical a year earlier: replacing Ethereum's EVM with RISC-V. The suggestion sparked immediate debate. But what most commentators missed was that Polkadot had already been building exactly this architecture for over a year—and was months away from deploying it to production.

Polkadot's JAM (Join-Accumulate Machine) isn't just another blockchain upgrade. It represents a fundamental rethinking of what a "blockchain" even means. Where Ethereum's worldview centers on a global virtual machine processing transactions, JAM eliminates the transaction concept entirely at its core layer, replacing it with a computation model that promises 850 MB/s data availability—42 times Polkadot's previous capacity and 650 times Ethereum's 1.3 MB/s.

The implications extend far beyond performance benchmarks. JAM may be the clearest articulation yet of a post-Ethereum paradigm for blockchain architecture.

The Gray Paper: Gavin Wood's Third Act

Dr. Gavin Wood wrote the Ethereum Yellow Paper in 2014, providing the formal specification that made Ethereum possible. He followed with the Polkadot White Paper in 2016, introducing heterogeneous sharding and shared security. In April 2024, he released the JAM Gray Paper at Token2049 in Dubai—completing a trilogy that spans the entire history of programmable blockchains.

The Gray Paper describes JAM as "a global singleton permissionless object environment—akin to Ethereum's smart-contract environment—paired with secure sideband computation parallelized over a scalable node network." But this undersells the conceptual shift.

JAM doesn't just improve on existing blockchain designs. It asks: what if we stopped thinking about blockchains as virtual machines entirely?

The Transaction Problem

Traditional blockchains—Ethereum included—are fundamentally transaction-processing systems. Users submit transactions, validators order and execute them, and the blockchain records state changes. This model has served well but carries inherent limitations:

• Sequential bottlenecks: Transactions must be ordered, creating throughput constraints
• Global state contention: Every transaction potentially touches shared state
• Execution coupling: Consensus and computation are tightly bound

JAM decouples these concerns through what Wood calls the "Refine-Accumulate" paradigm. The system operates in two phases:

Refine: Computation happens in parallel across the network. Work is divided into independent units that can execute simultaneously without coordination.

Accumulate: Results are collected and merged into global state. Only this phase requires consensus on ordering.

The result is a "transactionless" core protocol. JAM itself doesn't process transactions—applications built on JAM do. This separation allows the base layer to focus purely on secure, parallel computation.

PolkaVM: Why RISC-V Matters

At the heart of JAM sits PolkaVM, a purpose-built virtual machine based on the RISC-V instruction set. This choice has profound implications for blockchain computation.

The EVM's Architectural Debt

Ethereum's EVM was designed in 2013-2014, before many modern assumptions about blockchain execution were understood. Its architecture reflects that era:

• Stack-based execution: Operations push and pop values from an unbounded stack, requiring complex tracking
• 256-bit word size: Chosen for cryptographic convenience but wasteful for most operations
• Single-dimensional gas: One metric attempts to price vastly different computational resources
• Interpretation-only: EVM bytecode cannot be compiled to native code efficiently

These design decisions made sense as initial choices but create ongoing performance penalties.

RISC-V's Advantages

PolkaVM takes a fundamentally different approach:

Register-based architecture: Like modern CPUs, PolkaVM uses a finite set of registers for argument passing. This aligns with actual hardware, enabling efficient translation to native instruction sets.

64-bit word size: Modern processors are 64-bit. Using a matching word size eliminates the overhead of emulating 256-bit operations for the vast majority of computations.

Multi-dimensional gas: Different resources (computation, storage, bandwidth) are priced independently, better reflecting true costs and preventing mispricing attacks.

Dual execution modes: Code can be interpreted for immediate execution or JIT-compiled for optimized performance. The system chooses the appropriate mode based on workload characteristics.

Performance Impact

The architectural differences translate to real performance gains. Benchmarks show PolkaVM achieving 10x+ improvements over WebAssembly for arithmetic-intensive contracts—and the EVM is slower still. For complex, multi-contract interactions, the gap widens further as JIT compilation amortizes setup costs.

Perhaps more importantly, PolkaVM supports any language that compiles to RISC-V. While EVM developers are limited to Solidity, Vyper, and a handful of specialized languages, PolkaVM opens the door to Rust, C++, and eventually any LLVM-supported language. This dramatically expands the potential developer pool.

Maintaining Developer Experience

Despite the architectural overhaul, PolkaVM maintains compatibility with existing workflows. The Revive compiler provides complete Solidity support, including inline assembler. Developers can continue using Hardhat, Remix, and MetaMask without changing their processes.

The Papermoon team demonstrated this compatibility by successfully migrating Uniswap V2's contract code to the PolkaVM testnet—proving that even complex, battle-tested DeFi code can transition without rewrites.

JAM's Performance Targets

The numbers Wood projects for JAM are staggering by current blockchain standards.

Data Availability

JAM targets 850 MB/s of data availability—roughly 42 times the vanilla Polkadot capacity before recent optimizations and 650 times Ethereum's 1.3 MB/s. For context, this approaches the throughput of enterprise database systems.

Computational Throughput

The Gray Paper estimates JAM can achieve approximately 150 billion gas per second at full capacity. Translating gas to transactions is imprecise, but theoretical maximum throughput reaches 3.4+ million TPS based on the data availability target.

Real-World Validation

These aren't purely theoretical numbers. Stress tests have validated the architecture:

• Kusama (August 2025): Achieved 143,000 TPS at only 23% load capacity
• Polkadot "Spammening" (2024): Reached 623,000 TPS in controlled testing

These figures represent genuine transaction throughput, not optimistic projections or testnet conditions that don't reflect production environments.

Development Status and Timeline

JAM development follows a structured milestone system, with 43 implementation teams competing for a prize pool exceeding $60 million (10 million DOT + 100,000 KSM).

Current Progress (Late 2025)

The ecosystem has reached several critical milestones:

• Multiple teams have achieved 100% conformance with Web3 Foundation test vectors
• Development has progressed through Gray Paper versions 0.6.2 through 0.8.0, approaching v1.0
• The JAM Experience conference in Lisbon (May 2025) brought together implementation teams for deep technical collaboration
• University tours reached over 1,300 attendees across nine global locations, including Cambridge, Peking University, and Fudan University

Milestone Structure

Teams progress through a series of milestones:

1. IMPORTER (M1): Passing state-transitioning conformance tests and importing blocks
2. AUTHORER (M2): Full conformance including block production, networking, and off-chain components
3. HALF-SPEED (M3): Achieving Kusama-level performance, with access to JAM Toaster for full-scale testing
4. FULL-SPEED (M4): Polkadot mainnet-level performance with professional security audits

Multiple teams have completed M1, with several progressing toward M2.

Timeline to Mainnet

• Late 2025: Final Gray Paper revisions, continued milestone submissions, expanded testnet participation
• Q1 2026: JAM mainnet upgrade on Polkadot following governance approval via OpenGov referendum
• 2026: CoreChain Phase 1 deployment, official public JAM testnet, full network transition

The governance process has already shown strong community support. A near-unanimous DOT holder vote approved the upgrade direction in May 2024.

JAM vs. Ethereum: Complementary or Competitive?

The question of whether JAM represents an "Ethereum killer" misses the architectural nuance.

Different Design Philosophies

Ethereum builds outward from a monolithic foundation. The EVM provides a global execution environment, and scaling solutions—L2s, rollups, sharding—layer on top. This approach has created an enormous ecosystem but also accumulated technical debt.

JAM starts with modularity at its core. The separation of Refine and Accumulate phases, the domain-specific optimization for rollup handling, and the transactionless base layer all reflect a ground-up design for scalability.

Convergent Technical Choices

Despite different starting points, the projects are converging on similar conclusions. Vitalik's April 2025 RISC-V proposal acknowledged that the EVM's architecture limits long-term performance. Polkadot had already deployed RISC-V support to testnet months earlier.

This convergence validates both projects' technical judgment while highlighting the execution gap: Polkadot is shipping what Ethereum is proposing.

Ecosystem Realities

Technical superiority doesn't automatically translate to ecosystem dominance. Ethereum's developer community, application diversity, and liquidity depth represent substantial network effects that can't be replicated overnight.

The more likely outcome isn't replacement but specialization. JAM's architecture is optimized for certain workloads—particularly high-throughput applications and rollup infrastructure—while Ethereum retains advantages in ecosystem maturity and capital formation.

In 2026, they look less like competitors and more like complementary layers of a multi-chain internet.

What JAM Means for Blockchain Architecture

JAM's significance extends beyond Polkadot. It represents the clearest articulation of a post-EVM paradigm that other projects will study and selectively adopt.

Key Principles

Computation separation: Decoupling execution from consensus enables parallel processing at the base layer, not as an afterthought.

Domain-specific optimization: Rather than building a general-purpose VM and hoping it scales, JAM is architected specifically for the workloads blockchains actually run.

Hardware alignment: Using RISC-V and 64-bit words aligns virtual machine architecture with physical hardware, eliminating emulation overhead.

Transaction abstraction: Moving transaction handling to the application layer allows the protocol to focus on computation and state management.

Industry Impact

Whether JAM succeeds or fails commercially, these architectural choices will influence blockchain design for the next decade. The Gray Paper provides a formal specification that other projects can study, critique, and selectively implement.

Ethereum's RISC-V proposal already demonstrates this influence. The question isn't whether these ideas will spread, but how quickly and in what form.

The Road Ahead

JAM represents Gavin Wood's most ambitious technical vision since Polkadot itself. The stakes match the ambition: success would validate an entirely different approach to blockchain architecture, while failure would leave Polkadot competing with newer L1s without a differentiated technical narrative.

The next 18 months will determine whether JAM's theoretical advantages translate to production reality. With 43 implementation teams, a nine-figure prize pool, and a clear roadmap to mainnet, the project has resources and momentum. What remains to be seen is whether the complexity of the Refine-Accumulate paradigm can deliver on Wood's vision of a "distributed computer that can run almost any kind of task."

For developers and projects evaluating blockchain infrastructure, JAM merits serious attention—not as hype, but as a technically rigorous attempt to solve problems that every major blockchain faces. The blockchain-as-virtual-machine paradigm served the industry well for a decade. JAM bets that the next decade requires something fundamentally different.

---

Building on next-generation blockchain infrastructure? BlockEden.xyz provides high-performance RPC endpoints across the Polkadot ecosystem and 30+ other networks. Explore our API marketplace to access enterprise-grade infrastructure for your applications.