Reason Machines Open-Sources Aspen, a Git Server Built for AI Agents

Reason Machines has released Aspen, an open-source Git server for AI agent traffic.It targets repositories that hundreds of agents push to at once.Aspen independently implements the design OpenAI described for Pando.TL;DR Size: One Rust binary.

Branches live in PostgreSQL (or SQLite), packs live in object storage.Runs on: A laptop (aspen dev), one host via Docker Compose, or Helm and Terraform clouds.Performance: Pushes to different branches never wait on each other, and fetches reuse stored packs.

Best: 567 pushes per second sustained for 5 minutes on one 8-core server (self-reported).Worst: Landing on main runs at about 4 per second, and the project is pre-alpha.Bottom line: Best: per-branch writes remove the per-repository push ceiling.

Worst: no releases, no web UI, and the 24-hour durability gate is not met.What is Aspen?Aspen is a self-hostable Git server from Reason Machines that scales writes per branch, not per repository.It speaks plain Git over HTTPS and SSH.

Packs go to S3-compatible object storage; branch history goes to PostgreSQL.Why do classic Git servers struggle with AI agents?An agent pushes every few minutes, and CI fetches after each push.Per Reason Machines, a classic server queues every push to a repository together.

It also builds a fresh pack for every fetch.Server work grows with clients, not with new code.OpenAI hit this wall and built Pando.It cut median push latency by nearly 5x and serves nearly a petabyte daily.How does Aspen work?Aspen follows Pando and drops 2 claims most Git servers keep.

Per-branch compare-and-swap Each branch is a chain of versions in one Postgres row.A push uploads its pack, then moves the branch with one compare-and-swap.Pushes to different branches never wait for each other.If 2 pushes race on one branch, one wins.The other gets Git’s usual “fetch first” error.

The cost: branches may be read at slightly different moments.Stored packs instead of per-client packs Aspen never unpacks a push.It checks the pack, completes missing bases and stores it as-is.A fetch streams stored packs the client lacks, recompressing nothing.

Signed URLs can serve packs from a CDN.Trunk-only advertisement and compaction A push sees only the trunk branch, so negotiation stays small with a million branches.Background compaction merges packs 16 at a time, in levels like a log-structured merge tree.

A client far behind gets a few dozen packs, not thousands.Depth-1 CI fetches get a tip pack built once and served to every job.Auto play

Agentgit push CI jobgit fetch Aspenstateless server Postgres1 row per branch Object storagepacks as pushed Run 128 writersReset

Classic server: one queue per repo 0 / 128 done Aspen: one CAS per branch 0 / 128 done Toy model, not a benchmark. Amber = waiting, blue = done. Mirrors the illustrative simulation in the Reason Machines launch post. Pushes per second to one repository, each durable before acknowledgement

Cursor Origin, S3 Standard (published)120 <div class="