Ethereum Core Developers Forge Future of Network at Arctic Soldøgn Interop

This past week, the remote and starkly beautiful landscape of Longyearbyen, Svalbard, above the Arctic Circle, became the unlikely crucible for the future of the Ethereum blockchain. Over 100 Ethereum core contributors converged for the "Soldøgn Interop," an intensive week of collaborative development focused on hardening the upcoming "Glamsterdam" network upgrade. This gathering marked a significant milestone, culminating in critical advancements that promise to enhance Ethereum’s scalability, efficiency, and long-term sustainability.

The Soldøgn Interop, meaning "sun solstice" in Norwegian, aptly took place under the perpetual daylight of the Arctic summer, mirroring Ethereum’s own 24/7 operational ethos. This unique setting fostered an environment of unparalleled focus and collaboration, allowing developers from diverse client teams to work side-by-side. The interop successfully delivered on its three core objectives for Glamsterdam: establishing a credible post-upgrade gas limit floor of 200 million, achieving stable implementations of ePBS (encapsulated Proposer-Builder Separation) with external builders, and finalizing the repricing numbers for EIP-8037. Beyond Glamsterdam, meaningful progress was also made on features slated for the subsequent "Hegotá" upgrade, including FOCIL and native account abstraction, alongside a multitude of other vital topics.

The Arctic Crucible: A Unique Setting for Innovation

Svalbard, a Norwegian archipelago nestled deep in the Arctic Ocean, offers a backdrop unlike any other for a high-stakes technical summit. Its unusual status as a visa-free zone for all nationalities underscored Ethereum’s global and permissionless spirit. More profoundly, Svalbard is home to the Global Seed Vault and the Arctic World Archive, two subterranean cold-storage facilities designed to preserve humanity’s most critical data – from crop seeds to historical documents and, notably, a snapshot of Ethereum’s source code – for millennia. This symbolism resonated deeply with the developers, whose work aims to build a resilient, enduring digital infrastructure for the world. The constant daylight, a phenomenon from late April through August, facilitated round-the-clock work sessions, maximizing the intense week of development.

The Soldøgn event followed in the tradition of previous successful interops like Amphora, Edelweiss, and Nyota, returning to a focused, single-track format. Unlike the broader "Berlinterop" of the previous year, this structure allowed for concentrated, multi-client progress towards specific, well-defined goals for the Glamsterdam upgrade, ensuring rapid iteration and alignment across the ecosystem.

Glamsterdam Unveiled: The Path to Enhanced Scalability

At its heart, Glamsterdam represents Ethereum’s continued evolution towards greater scalability and efficiency. The primary objective of the Soldøgn Interop was to "harden" Glamsterdam implementations and establish a definitive target for a post-upgrade gas limit floor. The gas limit, a critical parameter governing the maximum computational work allowed in a single block, directly impacts network throughput and transaction capacity. Safely increasing this limit is a complex, multi-dimensional challenge that Glamsterdam addresses through several key mechanisms: optimizing how blocks are built and proposed, ensuring client implementations have sufficient headroom under increased load, and managing state-creation costs as throughput grows.

The practical outcome envisioned for the week was a stable, multi-client Glamsterdam development network running the latest specifications for ePBS, repricing, and block access lists. This would be coupled with robust benchmarking data to substantiate a credible proposal for the increased gas limit. Developers spent countless hours heads-down, immersed in coding, frequently working into the early morning, punctuated by focused breakout sessions to synchronize on design decisions and strategize for the longer-term roadmap.

Key Achievements and Technical Deep Dive

The achievements of the Soldøgn Interop can be segmented into three pivotal areas, all converging to enable the significant increase in Ethereum’s gas limit:

1. ePBS: Reshaping Block Construction
   Encapsulated Proposer-Builder Separation (ePBS) is a critical consensus layer (CL) component of Glamsterdam, designed to enhance the efficiency and fairness of block production. It refines the relationship between block proposers (validators) and block builders (specialized entities that construct transaction bundles), adding explicit deadlines for block construction, payload revelation, and attestations. This restructuring allocates more predictable time for execution, thereby increasing the "headroom" available to safely raise the gas limit.

   

   The week began with an ambitious goal: to establish a 4 Execution Layer (EL) x 4 Consensus Layer (CL) Glamsterdam devnet by Monday evening. Initial attempts revealed crucial issues, pushing the target to Tuesday, when a 4×3 configuration achieved sufficient stability for stress testing. The remainder of the week became an intensive ePBS hardening cycle: stress testing, identifying edge cases, implementing fixes, and repeating the process. A pivotal Builder API breakout session on Tuesday morning streamlined the specification around validator registration, the bid/header/commitments flow, the trust model for builder payments, and circuit-breaker behavior. Mid-week debugging efforts pinpointed cross-client edge cases, particularly concerning execution-request invalidation of beacon requests. A newly developed test suite exposed a universal gap across all client implementations, which was swiftly addressed. By Thursday, CL teams reported stable ePBS, with EL-side bid pathways resolving into Friday. Two key questions remain under active discussion: whether a request signature should commit to the receiving builder, and how to ensure the resilience of a 1 ETH-staked-builder design against P2P Sybil-based liveness attacks. By Friday, nearly all clients were running seamlessly together on glamsterdam-devnet-2, with the external builders pipeline thoroughly tested end-to-end.

2. BAL Optimizations: Fueling Parallel Processing
   On the execution layer side, Block-Level Access Lists (BALs), specified in EIP-7928, are a cornerstone of Glamsterdam’s scaling strategy. BALs provide clients with upfront information about a block’s read/write set, enabling crucial optimizations such as parallel transaction execution, batched I/O operations, and parallel state-root computation. These capabilities collectively determine how large a block clients can efficiently process, directly impacting the network’s overall throughput.

   The Soldøgn BAL track operated on dedicated devnets, separate from the ePBS chains, to ensure that optimization benchmarks were not conflated with consensus-layer stabilization efforts. Each optimization was implemented behind its own feature flag, allowing for isolated comparison and measurement. The BAL benchmark dashboard and leaderboard were instrumental in highlighting each client’s worst-case scenarios across the test suite. By prioritizing the slowest paths for improvement, teams could effectively raise the gas limit floor across the entire ecosystem, rather than just for the most performant implementations.

3. Gas Repricings: Sustainable State Growth
   Glamsterdam also introduces several execution layer gas repricings, recalibrating operational costs to more accurately reflect resource usage at higher throughputs. EIP-8037, a significant increase in state-creation gas cost, is central to this effort. Its purpose is to raise the price of writing new state, preventing a higher gas limit from translating into uncontrolled state growth and ensuring the network’s long-term health.

   

   Prior to Soldøgn, EIP-8037’s specification featured dynamic per-state-byte pricing tied to the block gas limit, which complicated testing and benchmarking significantly. Early in the week, teams unanimously agreed to abandon dynamic pricing in favor of a fixed cost_per_state_byte, with future repricing adjustments to be handled at subsequent hard fork boundaries. The accounting model itself underwent an iterative refinement process throughout the week. A Monday breakout shifted state-gas accounting from mid-execution to end-of-call-frame. A Tuesday follow-up addressed account creation costs, code deposit costs, and CREATE-transaction reverts. Wednesday’s discussions surfaced complex reservoir refund/refill edge cases, prompting a fundamental re-evaluation. By Thursday, accounting reverted to the opcode level, as it was determined that the primary complexity lay in the reservoir model itself. By Friday, the specification had stabilized on bal-devnet-6, with the BAL track delivering the final repricing numbers. This rapid iteration and resolution of complex technical issues exemplifies the immense value of interop events, compressing what might take months of asynchronous progress into just days.

The 200 Million Gas Limit: A Milestone for Ethereum

By Friday, the intensive work across ePBS, BAL optimizations, and gas repricings converged on a headline achievement: a credible 200 million post-Glamsterdam gas limit floor. This represents a substantial increase in Ethereum’s block capacity. The ePBS design provides the necessary structural time within a slot for increased execution, BAL optimizations grant clients the throughput headroom to manage this expanded capacity, and EIP-8037 ensures that the higher gas limit does not lead to unsustainable state bloat. This collective progress signals a significant step forward in Ethereum’s journey towards a more scalable and efficient network.

Strategic Decisions and Future Horizons

Beyond the core Glamsterdam work, the Soldøgn Interop served as a forum for crucial strategic discussions and the initial laying of groundwork for future upgrades.

Glamsterdam’s Evolving Landscape: Core contributors finalized decisions on several smaller Glamsterdam EIPs. EIP-8061 (exit/consolidation churn increase) was included in glamsterdam-devnet-1. EIP-8080 (exits via the consolidation queue) was declined for inclusion. EIP-8045 (slashed-validator duty removal) was narrowed in scope to only proposer duties within the look-ahead window. EIP-7688 (SSZ stable containers) remains within Glamsterdam’s scope but was held out of glamsterdam-devnet-1 to allow teams to address issues related to bounded gossip-message size for attestations under progressive lists.

A significant outcome was the deferral of EIP-8237 (an EL/CL sync architecture improvement) out of Glamsterdam. This decision preserves optionality for a more comprehensive "top-up sync" architecture in a future fork. In its place, attendees agreed to draft a new EIP that standardizes forkchoiceUpdated, newPayload, and getPayload sequencing, specifies a snap-sync initiation handshake, and tightens valid/invalid consistency across engine API surfaces. Hardening remained a consistent theme, with a dedicated session covering fork-choice compliance testing frameworks, the "Diamond" repository of reproducible CL edge-case scenarios, and "buildoor," EthPandaOps’ external-builder testing tool, which demonstrated attack scenarios suggested by attendees in real-time.

Beyond Glamsterdam: Glimpses of Hegotá and Future Forks: Several breakout sessions peered into the future, specifically addressing the "Hegotá" upgrade and subsequent developments. A proposal-agnostic session on native Account Abstraction explored the fundamental requirements and constraints for any future design. Key feature goals included alternative signature schemes, aggregation, batching, recovery, gas sponsorship, and flexible nonces, all balanced against critical constraints such as public-mempool compatibility, statelessness, and Layer 2 (L2) Denial-of-Service (DoS) resistance.

A Thursday breakout on FOCIL (Fork-Choice Incentive Layer) provided updates on implementation progress, with early prototypes already functional. Multi-client interop and a dedicated FOCIL devnet were identified as immediate next steps. Two notable design decisions emerged: disabling FOCIL during 2-epoch non-finality (mirroring proposer-boost circuit-breaker behavior) and adopting an index-based bookmark approach to ensure compatibility with frame transactions and EIP-7702.

Further out, a long-running ETH P2P track sketched out a QUIC-based replacement for libp2p, designed with privacy-by-default and slot-aware integration. An erasure-coded broadcast prototype demonstrated impressive performance, simulating approximately 6x faster propagation than GossipSub for 2.4 MB payloads. The CL track also expressed a strong sentiment towards eventually deprecating validator consolidations entirely, proposing a final fork that supports them before requiring exit-then-redeposit for subsequent validator management. This aims to provide a cleaner long-term solution to validator-set state growth.

Refining the Core Development Process

Mid-week, Nixo and Ansgar, the co-leads of the AllCoreDevs Execution (ACDE) calls, facilitated a session to gather input on the core development process itself. Discussions revisited the "headliner construct," debated the utility of a "strawmap" for future development, and formalized the EIP SFI (Specification Freeze Index) criteria. The consensus was to retain headliners but introduce more flexibility, accepting "theme + candidate EIP" as a viable pattern. The year assignments in the straw map beyond 2026 were deemed overly prescriptive and likely to be softened. A new four-point SFI definition was proposed, with AllCoreDevs Testing (ACDT) signaling readiness and ACDE/AllCoreDevs Consensus (ACDC) retaining the final call. A new prioritization-ordering process, to be produced after Call for Inclusion (CFI) decisions and reflected in the meta-EIP, will replace SFI’s traditional role in driving devnet inclusion, starting with Hegotá.

In terms of call coordination, Alex Stokes announced a three-month sabbatical, with Pari stepping in to moderate ACDC calls in the interim, and Barnabas filling in for ACDT. The current leadership structure now sees Nixo and Ansgar chairing ACDE, Pari as interim ACDC moderator, and Mario, Barnabas, and Danceratopz rotating ACDT moderation.

Operational Backbone: The Teams Behind the Scenes

The success of the Soldøgn Interop was significantly bolstered by the dedicated infrastructure provided by several Ethereum Foundation (EF) teams. EthPandaOps delivered ethIQ and a panda MCP server, vital tools for supporting the teams’ agentic workflows. Protocol Support meticulously set up soldogn.xyz as the central hub for interop goals, schedules, and notes. The EF Digital Studio team was on-site, capturing the entire week on film, promising the very first interop documentary to chronicle this historic gathering. Beyond these, teams used the in-person time to advance numerous other initiatives, from developing better test harnesses that compressed Hive feedback loops from hours to minutes, to improving engine-API plumbing (gossip deduplication, batched calls, light-client-driven head discovery), and navigating complex tradeoffs around client diversity. The comprehensive list of session notes is publicly available at soldogn.xyz.

Looking Ahead: From Prototypes to Production

With the intense week of Soldøgn Interop now concluded, the focus shifts to translating these prototypes and aligned decisions into production-ready code. The coming weeks will be dedicated to hardening client implementations against the newly finalized specifications, ensuring robust test coverage, and merging the numerous draft pull requests into the main codebase.

Crucially, the final decisions for critical values such as the 200 million gas limit target and the definitive repricing numbers will be publicly deliberated and formalized during the upcoming AllCoreDevs calls. These calls are expected to be the primary forum for discussing and ratifying the outcomes of Soldøgn, marking the official steps towards the Glamsterdam upgrade.

The Soldøgn Interop stands as a testament to the power of concentrated, collaborative effort within the Ethereum ecosystem. The dedication of over 100 core contributors, working under the midnight sun at 78°N, has propelled Ethereum significantly closer to its vision of a more scalable, efficient, and sustainable decentralized future. Special recognition goes to EthPandaOps for their organizational prowess and to all participants, including the Ethrex crew who joined their first interop, for their tireless work in this remarkably productive week.