This past week, just over 100 Ethereum core contributors gathered above the Arctic Circle – in Longyearbyen, Svalbard – for the Soldægn Interop: a week of intense work on the Glamsterdam network upgrade. This significant event, reminiscent of previous intensive interop sessions like Berlinterop, Amphora, Edelweiss, and Nyota, focused on a single, critical objective: hardening the upcoming Glamsterdam network upgrade. The outcome of this concentrated effort is poised to be a pivotal moment in Ethereum’s scaling roadmap, with key decisions made regarding gas limits, proposer-builder separation (ePBS), and execution layer (EL) optimizations.
The choice of Longyearbyen, Svalbard, as the venue for Soldægn Interop was deliberate and symbolic. Svalbard, a Norwegian archipelago in the Arctic Ocean, is uniquely positioned as a place where individuals from any nation can reside and work without visa requirements. This inclusive environment fosters a sense of global collaboration, mirroring Ethereum’s decentralized ethos. Furthermore, the region is home to the Svalbard Global Seed Vault and the Arctic World Archive, facilities dedicated to long-term preservation of humanity’s most vital resources, including digital heritage like Ethereum’s source code. The perpetual daylight during the Arctic summer, with the sun not setting from late April to August, provided a constant, 24/7 operational environment, a fitting parallel to Ethereum’s own continuous uptime. This extended daylight allowed the core developers to maximize their productive hours, pushing code and discussions well into the "night."
The Soldægn Interop, structured as a single-track, focused effort, aimed to drive multi-client progress towards the Glamsterdam upgrade. By Friday, the assembled developers had achieved three primary goals: establishing a consensus on a post-Glamsterdam gas limit floor of 200 million, ensuring stable implementations of Proposer-Builder Separation (ePBS) with external builders, and finalizing the repricing numbers for Ethereum Improvement Proposal (EIP) 8037. Beyond these headline achievements, substantial headway was also made on future features, including Hegotæi advancements such as Fee-Oblivious Contract Interaction Logic (FOCIL) and native account abstraction, alongside a host of other critical topics.
Harden Glamsterdam, Scale Ethereum: The Core Objectives
The overarching objective of the Soldægn week was to solidify the Glamsterdam network upgrade and establish a clear target for the gas limit that would be implemented post-upgrade. Safely increasing Ethereum’s gas limit is a complex, multi-faceted challenge. Glamsterdam addresses several key aspects of this challenge: it refines how blocks are constructed and proposed, enhances the headroom available for client implementations under load, and optimizes how state-creation costs scale in proportion to increased transaction throughput.
In practical terms, the week concluded with a stable, multi-client Glamsterdam development network (devnet) operational. This devnet was running the latest versions of ePBS, incorporating updated block access list specifications, and generating crucial benchmarking data. This data serves as the foundation for proposing a credible and robust increase in the gas limit. The developers dedicated the majority of their time to intensive coding, often working late into the early morning hours. These coding sprints were interspersed with targeted breakout sessions to align on critical design decisions and to deliberate on longer-term roadmap items for the Ethereum protocol.
Three Ethereum Foundation (EF) teams provided essential infrastructure and support throughout the interop. EthPandaOps deployed ethIQ, a performance monitoring tool, and a "panda" Message Compression Protocol (MCP) server to facilitate agentic workflows for the development teams. The Protocol Support team established soldogn.xyz as the central hub for tracking interop goals, schedules, and meeting notes, ensuring a single source of truth for all participants. Additionally, the EF Digital Studio team documented the entire week’s proceedings, with a documentary on the interop experience anticipated as a valuable historical record.
ePBS: Re-architecting Block Production for Enhanced Throughput
A significant portion of the Soldægn effort was dedicated to the refinement of Proposer-Builder Separation (ePBS). ePBS represents a fundamental shift in how blocks are constructed and proposed on Ethereum. It introduces explicit deadlines for various stages of block production, including construction, payload reveal, and attestation submission. This structured approach provides crucial time allocations for execution, thereby increasing the potential headroom for raising the gas limit.
The week commenced with an ambitious target: establishing a four-execution-layer (EL) to four-consensus-layer (CL) Glamsterdam devnet by Monday evening. The initial attempts revealed a number of challenges, necessitating a push of this target to Tuesday. By Tuesday, a four-by-three configuration was running stably enough to commence stress testing.
The remainder of the week evolved into a rigorous ePBS hardening cycle: stress testing, identifying edge cases, implementing fixes, and repeating the process. A breakout session on Tuesday morning significantly simplified the Builder API specification, clarifying validator registration, the bid/header/commitments flow, the trust model for builder payments, and circuit-breaker mechanisms. Mid-week debugging efforts zeroed in on cross-client edge cases, particularly concerning the invalidation of beacon requests based on execution layer requests. A newly developed test suite highlighted discrepancies across all client implementations in this area. By Thursday morning, CL teams reported stable ePBS operations, while EL-side bid pathways were still undergoing debugging. These issues were resolved through Thursday and into Friday. Two persistent, contentious questions for the All-Core-Devs (ACD) working group remained: whether a request signature should explicitly commit to the receiving builder, and how to design a resilient system for 1 ETH-staked builders against peer-to-peer Sybil-based liveness attacks.
By Friday, nearly all participating clients were successfully running on glamsterdam-devnet-2, with the external builder pipeline tested end-to-end, marking a significant milestone in ePBS development.
BAL Optimizations: Unlocking Execution Layer Throughput
While ePBS addresses the consensus layer’s role in scaling, the execution layer’s counterpart involves two primary components: gas repricings and Block-Level Access Lists (BALs), as defined in EIP-7928. BALs provide clients with upfront information about a block’s read and write sets, enabling critical optimizations such as parallel execution, batched input/output operations, and parallel state-root computation. These optimizations are directly correlated with the maximum block size that 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 consensus-layer stabilization efforts. Each optimization was implemented behind its own feature flag, allowing the week’s measurement work to compare them in isolation rather than as a monolithic bundle. The BAL benchmark dashboard and leaderboard, accessible at nerolation.github.io/bal-dashboard/, highlighted the worst-case scenarios for each client across the test suite. By focusing on improving the slowest execution paths first, the teams aimed to elevate the gas limit floor across the board, rather than solely benefiting the fastest client implementations.
Gas Repricings: Calibrating Costs for Higher Throughput
Glamsterdam incorporates several execution-layer gas repricings, meticulously calibrating costs to better align with resource utilization at higher transaction volumes. EIP-8037, which mandates an increase in state-creation gas costs, is central to this effort. This EIP raises the price associated with writing new state, ensuring that a higher gas limit does not lead to unbounded state growth on the network.
Leading up to the Soldægn interop, the EIP-8037 specification included dynamic per-state-byte pricing that was contingent on the block gas limit. This dynamic pricing model presented significant challenges for testing, creating a combinatorial explosion of test matrices for each gas limit band, and rendering benchmarking nearly intractable. Early in the week, the teams reached a consensus to abandon dynamic pricing in favor of a fixed cost_per_state_byte. Future repricing adjustments will be handled at future fork boundaries rather than within the current fork.
The accounting model itself underwent a more iterative refinement process. A breakout session on Monday shifted state-gas accounting from mid-execution to the end of call frames. A follow-up session on Tuesday addressed account creation costs, code deposit costs, and CREATE transaction reverts. By Wednesday, edge cases related to reservoir refunding and refilling necessitated a re-evaluation of the model. A breakout session on Thursday reverted the accounting back to the opcode level, recognizing that the primary complexity resided within the reservoir model, not the accounting computation itself. By Friday, the specification had stabilized on bal-devnet-6, with the BAL track delivering the final repricing numbers.
This entire process underscores one of the most vital aspects of interop events: the capacity to resolve complex specification, implementation, testing, debugging, and design issues within hours rather than weeks. At their most effective, interop weeks can compress months of asynchronous progress into a single day.
By Friday, the three distinct development threads – ePBS, BAL optimizations, and gas repricings – converged on a key outcome: a credible 200 million gas limit floor for the post-Glamsterdam era. This substantial increase is achievable due to the synergistic improvements: ePBS re-architects the slot to allocate more time for execution; BAL optimizations provide clients with the necessary throughput headroom within that structure; and EIP-8037 ensures that the increased gas limit does not result in uncontrolled state growth.
Other Glamsterdam Threads: Evolving the Protocol
Beyond the primary focus on ePBS, BALs, and gas repricings, the Soldægn interop addressed numerous other facets of the Glamsterdam upgrade through breakout sessions.
Consensus layer (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 Glamsterdam. EIP-8045, concerning the removal of slashed validator duties, was scoped down to only apply to proposer duties within the look-ahead window. EIP-7688, focusing on SSZ stable containers, remains within Glamsterdam’s scope but was held out of glamsterdam-devnet-1 to allow teams to address bounded gossip message sizes for attestations under progressive lists.
A synchronization architecture breakout session between EL and CL teams 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. This EIP will also specify a snap-sync initiation handshake and tighten consistency between the engine API surfaces for valid and invalid states.
Hardening and testing were consistent themes throughout the week. A session on Thursday focused on fork-choice compliance testing frameworks, the Diamond repository which houses reproducible CL edge-case scenarios, and buildoor, EthPandaOps’s external builder testing tool. During a mid-session demonstration, attendees actively suggested attack scenarios, which were immediately tested.
Beyond Glamsterdam: Charting the Future of Ethereum
Several breakout sessions looked ahead to Hegotæi and subsequent network upgrades. A deliberately proposal-agnostic session on native Account Abstraction initiated discussions by exploring the 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 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 notable design decisions were made: disabling FOCIL during two-epoch non-finality periods (mirroring proposer-boost circuit-breaker behavior) and adopting an index-based bookmark approach for compatibility with frame transactions and EIP-7702.
Further out on the roadmap, a long-running Ethereum Peer-to-Peer (ETH P2P) track sketched out plans for a QUIC-based replacement for libp2p, emphasizing privacy-by-default and slot-aware integration. A prototype for erasure-coded broadcast demonstrated approximately six times faster propagation than GossipSub on 2.4 MB payloads. The CL track also surfaced a strong sentiment towards eventually deprecating consolidations entirely. This approach would involve declaring a final fork that supports consolidations, followed by a mandatory exit-and-redeposit procedure, presenting a cleaner long-term solution to validator-set state growth.
ACD Process: Refining Governance and Prioritization
On Wednesday afternoon, Nixo and Ansgar, the two All-Core-Devs (ACD) co-leads, facilitated a session to gather input from core contributors regarding the ACD process. The session revisited the "headliner" construct, debated the merits of a strawmap, and formalized EIP Specification Framework Interface (SFI) criteria. The consensus was to retain headliners but to relax the rigidity between EIPs and themes, accepting a "theme plus candidate EIP" as a viable pattern. The strawmap’s per-fork year assignments beyond 2026 were flagged as overly canonicalized and likely to be softened. A new four-point SFI definition was proposed, with the All-Core-Devs Technical direction (ACDT) signaling readiness and the All-Core-Devs Execution (ACDE) and All-Core-Devs Coordination (ACDC) retaining the final decision-making authority. A new prioritization and ordering process, to be implemented after CFI decisions and reflected in the meta-EIP, will replace SFI’s previous role in driving devnet inclusion, commencing with the Hegotæi upgrade.
In terms of call coordination, Alex Stokes announced a three-month sabbatical commencing the following week. Pari will assume ACDC moderation duties in the interim, and Barnabas will fill in for ACDT. The interim leadership structure sees Nixo and Ansgar chairing ACDE, Pari moderating ACDC, and Mario, Barnabas, and Danceratopz rotating ACDT moderation responsibilities.
Everything Else: A Myriad of Improvements
Beyond the major initiatives, teams leveraged the in-person gathering to make progress on a wide array of improvements. These included enhancing test harnesses to compress Hive feedback loops from hours to minutes, implementing engine API plumbing improvements such as gossip deduplication, batched calls, and light-client-driven head discovery, and making difficult trade-offs regarding client diversity. The full list of session notes is publicly available at soldogn.xyz.
Next Steps: From Interop to Production
Following the Soldægn interop, the participating teams are returning to their respective workstreams to transform the week’s prototypes into production-ready code. The coming weeks will be characterized by intense efforts to harden client implementations against the new specifications, finalize test coverage, and integrate the draft Pull Requests from Soldægn into the codebase.
As is customary, final decisions on key values, such as the 200 million gas limit target and precise repricing numbers, will be made and publicly announced during All-Core-Devs calls. These crucial decisions are expected to be the primary focus of upcoming discussions.
The success of the Soldægn Interop is a testament to the dedication and collaborative spirit of the Ethereum core contributors who traveled to the 78th parallel North. Special acknowledgment is due to EthPandaOps for their daily organizational efforts and to all who worked tirelessly under the midnight sun to achieve the daily goals. The event also marked the first interop for the Ethrex crew. The week was exceptionally productive, and the anticipation of a full short film documenting the experience promises a valuable historical record of this pivotal moment in Ethereum’s development.
