Just over 100 Ethereum core contributors recently converged in Longyearbyen, Svalbard, situated above the Arctic Circle, for the Soldægn Interop. This intensive week-long event was dedicated to critical development work on the upcoming "Glamsterdam" network upgrade, with a primary focus on enhancing scalability and fortifying the network’s infrastructure. The Soldægn Interop marked a return to a focused, single-track format, mirroring successful previous gatherings like Amphora, Edelweiss, and Nyota, all aimed at achieving specific, tangible progress towards major network upgrades.
The strategic choice of Svalbard for this critical summit underscores a unique blend of logistical and symbolic considerations. As one of the few locations globally where individuals can live and work without visa requirements, it fosters an environment of inclusivity for international contributors. More profoundly, Svalbard hosts the Global Seed Vault and the Arctic World Archive, facilities dedicated to preserving humanity’s heritage in cold storage. This juxtaposition of cutting-edge technological advancement with long-term data preservation resonated with the developers’ mission to build a robust and enduring blockchain infrastructure. Furthermore, the perpetual daylight during the late April to August period in Svalbard served as a potent metaphor for Ethereum’s commitment to 24/7 uptime, a principle the core developers actively embraced throughout their demanding schedule.
The Soldægn Interop, following last year’s Berlinterop, aimed to build upon previous advancements and address key challenges in scaling the Ethereum network. The primary objectives for the week were clear: to establish a stable post-Glamsterdam gas limit floor, ensure the robust functionality of proposer-builder separation (ePBS) implementations with external builders, and finalize critical repricing numbers for EIP-8037. By the conclusion of the event on Friday, these core goals were successfully met, laying a solid foundation for the Glamsterdam upgrade. Beyond these headline achievements, significant strides were also made in developing features for the subsequent "Hegotæ" upgrade, including advancements in Fee Market Changes (FOCIL) and native account abstraction, alongside discussions on numerous other crucial topics.
Harden Glamsterdam, Scale Ethereum
The overarching mission of the Soldægn Interop was to harden the implementations of the Glamsterdam upgrade and to establish a well-defined target for the gas limit floor in the post-upgrade era. Safely increasing the gas limit is a complex, multi-faceted challenge, and Glamsterdam addresses several key aspects. These include optimizing how blocks are constructed and proposed, ensuring that client implementations have sufficient operational headroom under load, and managing the scaling of state creation costs in tandem with increased throughput.
The week’s intensive work translated into practical outcomes: a stable, multi-client Glamsterdam development network (devnet) was established, running the latest ePBS configurations. Additionally, the specifications for repricing and block access lists (BALs) were finalized, and crucial benchmarking data was gathered to support a credible proposal for the gas limit increase. The majority of the developers’ time was dedicated to hands-on coding, often extending into the early morning hours. These coding sessions were interspersed with crucial breakout discussions to align on design decisions and strategize for the longer-term roadmap of the Ethereum protocol.
The Ethereum Foundation’s commitment to facilitating such collaborative events was evident through the dedicated support provided by several internal teams. EthPandaOps delivered essential infrastructure, including ethIQ for performance analysis and a panda MCP server to enhance agentic workflows. The Protocol Support team established soldogn.xyz as the central repository for interop goals, schedules, and detailed meeting notes, serving as a single source of truth for all participants. Furthermore, the EF Digital Studio team meticulously documented the entire week, with plans to release a documentary capturing the essence of this significant interop event.
ePBS: Enhancing Proposer-Builder Separation
A central pillar of the Glamsterdam upgrade is the refinement of proposer-builder separation (ePBS). This enhancement goes beyond merely streamlining the relationship between block proposers and builders; it fundamentally restructures block production by introducing explicit deadlines for block construction, payload reveal, and attestation finalization. This architectural shift allocates dedicated time for the execution layer, thereby creating increased headroom for raising the gas limit.
The week commenced with an ambitious target: a stable 4 Execution Layer (EL) / 4 Consensus Layer (CL) Glamsterdam devnet by Monday evening. Initial attempts revealed a number of challenges, necessitating a push of the target to Tuesday. By Tuesday, a 4×3 configuration was running stably, allowing the commencement of rigorous stress testing. The remainder of the week was dedicated to an iterative ePBS hardening cycle: stress testing, identifying edge cases, implementing fixes, and repeating the process.
A significant breakthrough occurred during a Tuesday morning breakout session focused on the Builder API. This session substantially simplified the specification surrounding validator registration, the bid/header/commitments flow, the trust model for builder payments, and the implementation of circuit-breaker mechanisms. Mid-week debugging efforts concentrated on cross-client edge cases, particularly concerning the invalidation of beacon requests in response to execution layer requests. A newly developed test suite highlighted a critical gap present across all client implementations. By Thursday morning, CL teams reported stable ePBS functionality, while EL-side bid pathways were still undergoing debugging, with resolutions achieved by Friday. Two persistent technical debates within the AllCoreDevs (ACD) community remained: whether a request signature should explicitly commit to the receiving builder, and how to ensure the resilience of a 1 ETH-staked-builder design against peer-to-peer Sybil-based liveness attacks. By Friday, nearly all participating clients were operating in unison on glamsterdam-devnet-2, with the external builder pipeline successfully tested end-to-end.
BAL Optimizations: Streamlining Execution Layer Throughput
While ePBS addresses the consensus layer’s contribution to Glamsterdam’s scaling strategy, the execution layer’s role is defined by gas repricings and Block-Level Access Lists (BALs). By providing clients with upfront, detailed information about a block’s read and write sets, BALs facilitate parallel execution, batched I/O operations, and parallel state-root computation. These advancements are critical determinants of the maximum block size clients can comfortably process.
The BAL track at Soldægn operated on separate devnets, distinct from the Glamsterdam ePBS chains, ensuring that optimization benchmarks were not conflated with the stabilization efforts of the consensus layer. Each optimization was implemented behind its own feature flag, allowing for isolated comparative analysis rather than bundled testing. The BAL benchmark dashboard and leaderboard effectively highlighted each client’s worst-case performance scenarios across the entire test suite. By prioritizing the optimization of the slowest execution paths, developers aimed to systematically raise the gas limit floor across all implementations, rather than solely benefiting the most performant clients.
Gas Repricings: Calibrating Costs for Higher Throughput
Glamsterdam incorporates several gas repricing adjustments within the execution layer, recalibrating costs to better align with resource utilization at higher throughput levels. Central to these changes is EIP-8037, which increases the gas cost associated with creating new state. This measure is designed to prevent an unbounded expansion of network state, even with a significantly higher gas limit.
Leading into the Soldægn Interop, the EIP-8037 specification featured dynamic per-state-byte pricing that was directly tied to the block gas limit. This dynamic approach presented significant challenges for testing, requiring a complex fuzz matrix for each gas limit band, and made benchmarking nearly intractable. Early in the week, the development teams reached a consensus to abandon dynamic pricing in favor of a fixed cost_per_state_byte. Future repricing adjustments will be handled at fork boundaries rather than being dynamically adjusted within a single fork.
The accounting model itself underwent a more iterative development process. A breakout session on Monday shifted state-gas accounting from mid-execution to the end of the call frame. A subsequent follow-up on Tuesday addressed account creation costs, code deposit costs, and CREATE-transaction reverts. Wednesday brought to light edge cases related to reservoir refunds and refills, necessitating a re-evaluation of the model. A breakout session on Thursday reverted accounting to the opcode level, with the conclusion that the primary complexity resided within the reservoir model, not the accounting computation itself. By Friday, the specification had stabilized on bal-devnet-6, and the BAL track successfully delivered the final repricing numbers.
This entire development arc exemplifies a crucial aspect of interop events: the ability to resolve complex issues spanning specification, implementation, testing, debugging, and design in a matter of hours rather than weeks. At their most effective, these interop weeks can compress months of asynchronous progress into each individual day.
The culmination of these efforts at Soldægn was the establishment of a credible 200 million gas limit floor for the post-Glamsterdam era. This substantial increase is achievable due to the synergistic effects of ePBS, which structures the block production slot to afford the execution layer more time; BAL optimizations, which provide clients with the necessary throughput headroom within that structure; and EIP-8037, which ensures that the increased gas limit does not lead to uncontrolled state growth.
Other Glamsterdam Threads: Evolving the Protocol
Beyond the core advancements in ePBS, BALs, and gas repricings, a significant portion of the remaining Glamsterdam scope was addressed through various breakout sessions. CL teams finalized decisions on several smaller Glamsterdam EIPs. EIP-8061, which aims to increase exit and consolidation churn, was successfully integrated into glamsterdam-devnet-1. EIP-8080, proposing exits via the consolidation queue, was declined for inclusion in this upgrade. EIP-8045, concerning the removal of slashed validator duties, was scoped down to apply only to proposer duties within the look-ahead window. EIP-7688, focusing on SSZ stable containers, remains within the Glamsterdam scope but was held out of glamsterdam-devnet-1 while the team addressed bounded gossip message sizes for attestations under progressive lists.
A crucial EL/CL sync architecture breakout session on Wednesday morning resulted in the deferral of EIP-8237 from Glamsterdam. This decision was made to preserve optionality for a more comprehensive "top-up sync" architecture in a future fork. In its place, the participants agreed to draft an EIP that standardizes the sequencing of forkchoiceUpdated, newPayload, and getPayload calls, specifies an initiation handshake for snap-sync, and enhances consistency between the engine API surfaces for valid and invalid states.
Hardening and testing remained a constant theme throughout the week. A dedicated session on Thursday focused on fork-choice compliance testing frameworks, the Diamond repository—a collection of reproducible CL edge-case scenarios—and buildoor, PandaOps’s external builder testing tool. During a mid-session demonstration, attendees proposed numerous attack scenarios on the spot, which were then simulated and analyzed.
Beyond Glamsterdam: Charting the Future
Several breakout sessions at Soldægn looked beyond the immediate Glamsterdam upgrade towards "Hegotæ" and subsequent forks. A proposal-agnostic session on native Account Abstraction initiated discussions on the fundamental requirements and constraints that any future design must satisfy. Feature-set goals, including alternative signature schemes, aggregation, batching, recovery, gas sponsorship, flexible nonces, and keystore wallets, were considered alongside critical hard constraints such as public mempool compatibility, statelessness, and Layer 2 Denial-of-Service (DoS) resistance.
A FOCIL breakout on Thursday focused on implementation updates. Early prototypes were already functional, with multi-client interop and a dedicated FOCIL devnet identified as immediate next steps. Two significant design decisions were made: disabling FOCIL during two-epoch non-finality periods, mirroring the behavior of the proposer-boost circuit breaker, and adopting an index-based bookmark approach to ensure compatibility with frame transactions and EIP-7702.
Looking further ahead, a long-running ETH P2P track explored the potential for a QUIC-based replacement for libp2p, emphasizing privacy-by-default features and slot-aware integration. Additionally, an erasure-coded broadcast prototype demonstrated approximately six times faster propagation speeds compared to GossipSub when handling 2.4 MB payloads. The CL track also revealed a strong sentiment towards the eventual deprecation of consolidations. The proposed approach involves declaring a final fork that supports them, followed by a mandatory exit and re-deposit mechanism, presenting a cleaner long-term solution to the challenge of validator-set state growth.
ACD Process: Refining Governance
On Wednesday afternoon, the co-leads of the AllCoreDevs Engineers (ACDE) working group, Nixo and Ansgar, convened a session to gather input from core contributors regarding the AllCoreDevs (ACD) process. The session revisited the "headliner" construct, debated the merits of maintaining a straw map, and formalized criteria for EIP Special Fork Inclusion (SFI). The consensus was to retain headliners but to loosen the rigidity between EIPs and themes, accepting a "theme plus candidate EIP" as a viable development pattern. The per-fork year assignments in the straw map beyond 2026 were flagged as overly canonicalized and likely to be softened. A new four-point SFI definition was proposed, with ACD Technical (ACDT) signaling readiness and ACDE/AllCoreDevs Coordination (ACDC) retaining the final decision-making authority. A new prioritization and ordering process, to be determined after Conflict-Free Irreducible (CFI) decisions and reflected in the meta-EIP, will supersede the previous role of SFI in driving devnet inclusion, commencing with the Hegotæ upgrade.
In terms of call coordination, Alex Stokes announced a three-month sabbatical commencing the following week. Pari will assume interim ACDC moderation duties, while Barnabas will fill in for ACDT. The current leadership structure for ACD calls comprises Nixo and Ansgar chairing ACDE, Pari as interim ACDC moderator, and Mario, Barnabas, and Danceratopz rotating ACDT moderation responsibilities.
Everything Else: A Broad Spectrum of Progress
In addition to the major developments discussed, teams utilized the in-person gathering to make progress across a wide array of topics. This included enhancing test harnesses, significantly compressing Hive feedback loops from hours to minutes, and implementing improvements to engine API plumbing, such as gossip deduplication, batched calls, and light-client-driven head discovery. Discussions also addressed complex tradeoffs related to client diversity and numerous other technical areas. A comprehensive list of session notes is publicly available at soldogn.xyz.
Next Steps: From Interop to Implementation
Following the productive Soldægn Interop, development teams are now returning to their respective organizations to transition the week’s prototypes into production-ready code. The coming weeks will be characterized by intensive efforts to harden client implementations against the new specifications, finalize test coverage, and merge the draft pull requests originating from Soldægn into the core codebase.
As is customary, the final decisions on critical values, such as the 200 million gas limit target and the precise repricing numbers, will be formally announced and shared publicly during AllCoreDevs calls. These discussions are anticipated to be the primary focus of upcoming protocol development meetings.
The success of the Soldægn Interop is a testament to the dedication and collaborative spirit of the Ethereum core contributors who traveled to the remote Arctic location. Special commendation is due to EthPandaOps for their instrumental role in organizing and energizing the group daily, and to all who worked tirelessly under the midnight sun to ensure the achievement of daily goals. The event also marked the first interop attendance for the Ethrex crew. The week was remarkably productive, and the upcoming short film promises to be a valuable chronicle of this significant milestone in Ethereum’s ongoing evolution.
