GitHub Project Rubicon: New Git Storage Hits ~5,000 Concurrent Agents and ~7,200 Pushes/sec in Internal Tests

Core Background & Industry Pain Points

Agents push busy repos from short write bursts into sustained concurrency: each agent waits on a push, and every write fans out to CI and other agents. GitHub says platform Git activity more than doubled from Sep 2025 to Aug 2026, with ~7.38B commits in Sep 2026. Legacy design couples durable replicas with read scale, so adding readers slows writers.

Architecture Highlights & Internals

Project Rubicon uploads immutable objects to Azure Blob first, then Ref-CAS commits a quorum CAS only on touched refs—most agents push private branches. Spokes routes onto disposable virtual replicas with rebuildable disk caches. Compaction and GC run on separate nodes against Blob/Ref-CAS.

Authoritative Benchmarks & Measured Scores

Vendor internal tests only: ~5,000 concurrent agents and ~7,200 pushes/sec on one repo with low-latency reads; an earlier series post cites up to ~35× write throughput. No third-party replication. Early Blob conditional-write prototypes topped mid-hundreds of writes/sec; Ref-CAS is described as tens of thousands of ref transactions/sec.

Developer Hands-on Guide

Push, fetch, branch, and protections stay the same. Limited private preview now; broader rollout aimed for early 2027. Follow-ons include clone-free file reads, an atomic multi-file commit API, event streams, and lighter clones. Follow the three-post Blog series; do not treat internal stress numbers as your repo SLA.