open_scion
Source control for the age of coding agents.
Anthropic built Scion, a faster version control system for coding agents,
and described it in
Redesigning source control:
a server-centric system built for hundreds of agents that read, write and land
code at the same time. Scion is internal to Anthropic and is not available to
the public.
So I built open_scion: an open-source version of that design that anyone can
run, and that the community can improve and maintain together.
MIT licensed. Vendor neutral: the server never calls a language model, and every
AI feature works with any provider, or none.
open_scion is an independent implementation of the publicly described design. It is not affiliated with or endorsed by Anthropic.
Why
Classic Git hosting was built for humans who clone a repository, work for hours
and push once. Coding agents work differently: thousands of short-lived tasks,
each touching a few files, each wanting to land in seconds, all on the same
branches. Full clones, merge queues and client-side history walks become the
bottleneck.
Scion's answer is to move the work to the server: clients stay online and fetch
only what they need, history questions are answered (and cached) by the server,
changes land through a compare-and-swap instead of a queue, every update is an
entry in a changeset log, and the repository state lives in a consistent
database plus object storage so servers scale out. open_scion implements these
ideas, with normal Git repositories underneath.
The Scion ideas, implemented
| Scion idea |
In open_scion |
| Always-online clients that fetch exactly what they need |
ObjectService serves single objects and sparse trees; graft clone and graft sparse materialize only the paths you ask for. |
| Source control as an API: history runs on the server |
Blame, path history, ancestry and code search run server-side and are memoized as derived data, computed once per commit. |
| Landing without a merge queue |
UserLand rebases a change onto the current tip and lands it with a compare-and-swap; concurrent lands on one branch are batched into a single reference update. |
| Automatic conflict resolution |
A conflicting land is resolved by a resolver you choose (any LLM provider, a deterministic tool, or none) through a versioned, vendor-neutral protocol. |
| Changeset log |
Every accepted reference update is recorded with its operation and actor in a dense, ordered log that clients list or watch live. |
| Storage core: a database and object storage, stateless servers |
Each change is a changeset in a write-ahead log in SQLite or PostgreSQL, with a compare-and-swap per reference; packs live in object storage (file, S3, GCS, Azure). Server nodes are caches that any node can rebuild, so you add nodes to scale. |
| Test after landing, revert the culprit |
graft-verify tests the tip, bisects a failure and reverts the change that broke it. |
| Monitoring agents ("superfans") |
Agents follow the changeset stream and report what matters to each component, also through Slack. |
| Agent-friendly review |
Reviews with semantic approval rules: a comment-only change can need fewer approvals than a logic change. |
| Agents as first-class users |
Per-agent tokens, an RPC allowlist and branch policies decide what each agent may do. |
| Strict cache tiers |
graft-cache caches immutable objects in daemon and regional tiers, verifying every object. |
Architecture
agents, CI jobs, sparse workspaces graft CLI / Go SDK
|
v gRPC
+-------------------------------------------------+
| graft-cache (optional daemon and cache tiers) |
+------------------------+------------------------+
v
+---------------------------------------------------------------+
| open_scion server (any number of nodes) |
| land - objects - changesets - derived data - search - review |
| write path: changeset + compare-and-swap per reference |
+-----------+--------------------------------+------------------+
| |
v v
+-----------------------+ +-----------------------------+
| SQLite / PostgreSQL | | object storage |
| changeset WAL, refs, | | content-addressed packs |
| changelog, reviews | | (file, S3, GCS, Azure) |
+-----------------------+ +-----------------------------+
\ /
local Git repositories = caches any node can rebuild
Details: ARCHITECTURE.md and STORAGE.md.
Quick start
Requirements: Linux or macOS, Go 1.26, a C toolchain, Meson and Ninja (the
build compiles a bundled Git).
git clone https://github.com/feder-cr/open_scion.git
cd open_scion
make build # server, CLI and tools into _build/bin
examples/graft/quickstart.sh # a server, a cache daemon, two agents and a land, in a temporary directory
./_build/bin/graft # the CLI and its commands
To run your own server, adapt examples/graft/config.toml
and start it with _build/bin/gitaly serve config.toml. To put the repository
state in a database and object storage, add a [graft.storage] section: start in
shadow mode, import your repositories, then switch to authoritative
(STORAGE.md).
Inside the code the extensions are called Graft: the [graft]
configuration section, the graft CLI, internal/graft and doc/graft.
Documentation
Status
Version 0.1.0, the first public release. Everything above is implemented and
covered by unit, end-to-end, multi-node, crash and fuzz tests. Interfaces may
still change before 1.0. Known gaps (for example garbage collection of packs in
the storage core) are listed in LIMITATIONS.md.
open_scion is meant to be maintained by its community. Open an issue to report a
bug or propose an idea, start a discussion before a large design change, and send
pull requests: tests and a short description of the reasoning make them easy to
review. The design documents in doc/graft/PLAN*.md explain why things are the
way they are.
Credits and license
open_scion is MIT licensed, see LICENSE.
It started as a fork of Gitaly, GitLab's
Git RPC server (MIT, Copyright GitLab Inc.), which provides the Git plumbing
underneath; every upstream Gitaly RPC keeps working. The non-MIT ee/ directory
of upstream Gitaly is not part of this repository. Gitaly's own README is kept in
doc/UPSTREAM-GITALY.md, and third-party notices are in
NOTICE.
openscion 是一个采用 MIT 许可证的开源项目,对 Scion 进行了重新实现。Scion 是 Anthropic 内部为编程智能体开发但从未公开发布的以服务器为中心的版本控制系统。