OpenAI details Pando Git backend serving nearly 1 PB a day to Codex agents

OpenAI engineering published the architecture of Pando on 2 November 2026, detailing how it rebuilt internal Git hosting after parallel Codex coding agents pushed reliability on its legacy monorepo backend below 90%. Conventional replicated Git servers serialise reference updates through three-phase commits or a shared write-ahead log, turning millions of short-lived agent branches into a global lock bottleneck and inflating reference advertisements past 100 MiB.

Pando separates immutable packfiles in horizontally scalable blob storage from per-branch metadata logs enforced under causal consistency rather than global linearisability. When a developer or Codex worker pushes to a feature branch, Pando advertises only a designated trunk branch so clients upload thin deltas, keeping median push packfiles below 20 KiB and 99th-percentile pushes under 3 MiB. Fetch traffic reads immutable cached packfiles directly, hitting local disk caches on more than 99% of requests.

OpenAI has contributed client-side patches including parallel pack indexing and explicit force-with-lease object negotiation upstream to Git, while keeping the Pando server infrastructure internal.

Key numbers

• Nearly 5 times lower median Git push latency (roughly an 80% reduction).
• Nearly 1 PB of Git data served per day, peaking above 57 TB in a single hour.
• Under 20 KiB median push packfile size and under 3 MiB at the 99th percentile.
• Over 99% local disk cache hit rate on packfile fetches.