Solana Proposes Removing Block Limits: SIMD-0370 Ushers in Dynamic Scaling with Alpenglow

SIMD-0370 Proposal Introduction

Anza announced on September 27, 2025, the introduction of SIMD-0370, a proposal from Jump's Firedancer team to eliminate Solana's fixed compute unit (CU) block limits following the Alpenglow upgrade. This shift would allow validators to dynamically skip unprocessable blocks, unlocking variable block sizes based on hardware capabilities rather than static caps, addressing historical congestion and paving the way for unprecedented network throughput.

Evolving Solana's Block Processing Framework: What Is SIMD-0370?

SIMD-0370 is a Solana Improvement Document proposing the removal of predefined CU limits per block after Alpenglow's implementation, Solana's most significant consensus overhaul since inception. Rooted in Solana's early 2021 designs to mitigate denial-of-service risks, fixed limits have constrained the network through events like 2022 outages from NFT mint floods and April 2024's 75% block drop rate due to spam. The proposal leverages Alpenglow's sub-second finality (100-150ms) to enable producers to pack maximum transactions, with validators skipping if execution exceeds slot times, fostering a self-optimizing ecosystem.

Key Components of SIMD-0370

• Elimination of static CU caps (currently 60M, proposed 100M via SIMD-0286), allowing faster validators to produce larger blocks without artificial ceilings.
• Validator skipping mechanism where nodes vote to bypass unexecutable blocks, maintaining chain progression while incentivizing upgrades.
• Performance flywheel effect: Block producers maximize fees by including more transactions, validators skipping lose rewards, driving hardware and code optimizations for broader capacity.
• Integration with Alpenglow, ditching TowerBFT and Proof-of-History for Web2-comparable speeds, and Firedancer's 10x gains to handle variable loads.
• Safeguards against centralization, including epoch-shortening to address mid-epoch speed gaps and adherence to Amdahl's Law for realistic speedup expectations.

Benefits to Users and the Solana Ecosystem

For Users: Dynamic blocks reduce congestion risks, as seen in 2024 memecoin spikes, enabling smoother DeFi interactions like swaps and staking with fewer failed transactions and lower fees during peaks.

For the Ecosystem: This enhances decentralization by distributing load based on capability, countering stake concentration in data centers, while boosting MEV opportunities and revenues without Ethereum-like extraction pitfalls, ultimately supporting over 2,000 validators and accelerating runtime improvements like 2024's halved replay times.

Historical Evolution of Solana's Block Limits and Performance Challenges

Solana's block limits originated in early 2021 as a protective measure against denial-of-service attacks, establishing fixed compute unit (CU) caps to maintain network stability during its nascent phase. However, these constraints were tested repeatedly, culminating in multiple outages throughout 2022 triggered by overwhelming NFT minting activity that flooded the chain with transactions, exposing the limits' inadequacy for high-demand scenarios. The crisis escalated in April 2024, when network congestion peaked due to spam transactions, resulting in a staggering 75% block drop rate; this prompted immediate emergency patches and validator optimizations to mitigate the fallout, including software tweaks to prioritize legitimate traffic and hardware recommendations for operators to handle spikes more effectively.

In response to these pressures, Solana began implementing gradual CU limit increases starting in December 2024, elevating the cap from 48 million to 50 million under SIMD-0207 as an initial step to alleviate bottlenecks without risking instability. This cautious escalation continued into July 2025, when the limit was further raised to 60 million to specifically address memecoin-driven activity surges, which had become a recurring source of congestion; these hikes provided short-term relief by allowing more transactions per block, reducing failed inclusions and improving user experience for DeFi applications like swaps and staking during volatile periods.

Building on these foundations, Solana unveiled Alpenglow in May 2025, marking the network's most substantial consensus overhaul to date. This upgrade dramatically reduces finality times to just 100-150 milliseconds by abandoning the legacy TowerBFT and Proof-of-History mechanisms in favor of a streamlined protocol that achieves speeds comparable to traditional Web2 systems, such as centralized databases or payment processors. Alpenglow's efficiency enables more flexible block processing, setting the stage for dynamic scaling where validators can adapt to varying loads without rigid caps, thus resolving long-standing latency issues that plagued earlier versions.

Complementing this, Firedancer's testnet debut in early 2025 introduced promises of up to 10x performance improvements over existing clients, directly tackling historical bottlenecks like execution delays and spam vulnerability. By optimizing code for variable workloads, Firedancer empowers validators to manage diverse transaction volumes efficiently, eliminating the need for fixed limits and allowing the network to self-regulate based on real-time capabilities—practical benefits include faster confirmation for DeFi trades and reduced risks of chain halts, making Solana more robust for high-throughput applications.

Maximizing Network Participation with SIMD-0370

Upgrade hardware (e.g., faster CPUs for execution) to minimize skips and maximize rewards, while collaborating on client optimizations between Agave and Firedancer teams. For developers, simulate dynamic loads in devnet to build resilient dApps, ensuring your protocols adapt to varying block sizes without fixed assumptions.

Conclusion

SIMD-0370 represents a bold evolution for Solana, transitioning from rigid limits to capability-driven scaling post-Alpenglow, promising enhanced throughput and resilience. By incentivizing upgrades and mitigating historical bottlenecks, this proposal strengthens Solana's DeFi dominance, offering users and validators practical paths to a more efficient, decentralized future.