In April 2026, delivered the Batcher Validation-Only Mode in the sequencer repo (starkware-libs/sequencer). Introduced a new configuration option 'validation_only' that allows the batcher to validate proposed blocks without building proposals. This involved updates to configuration files, the validation logic, and corresponding tests to ensure correct behavior when validation_only is enabled. The work is implemented across the batcher and node config components, with documentation updates to reflect the new option. Commit references: 0773e658c72417fa912296627a92ef873a8d64b6 and 53b6f0a6f6783787938354d76dda4da780de55e0. Overall impact: enables faster validation paths, reduces resource use on validator nodes, and improves testing coverage for validation-only configurations. Skills demonstrated: configuration management, feature flag/option design, validation logic, test coverage, and cross-functional collaboration with documentation.