You do not need to convert an existing Git repository just because Git 3.0 is proposed. The Git project’s proposal would make SHA-256 the default object format and reftable the default reference backend for newly initialized repositories. As of the proposal dated October 7, 2026, Git 3.0 has no planned release date, and those defaults depend on ecosystem readiness. Treat migration as a separate compatibility and operations decision—not as a requirement that comes with the release.
What Git 3.0 is proposing—and what it is not
The proposed change affects defaults for repositories created under Git 3.0:
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- Object format: SHA-256 instead of SHA-1.
- Reference storage: reftable instead of the
filesbackend.
These are separate choices. SHA-256 changes how repository objects are identified; reftable changes how references and their logs are stored. A repository can use SHA-256 without reftable, or reftable without changing its object format. The proposal does not say existing SHA-1 repositories must be converted, and it does not plan to deprecate SHA-1 at this time.
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The Git project says there is no planned release date for Git 3.0. Its proposal makes ecosystem readiness a prerequisite, including support in libraries, applications, forges and alternative Git implementations. The defaults are therefore proposals, not a release schedule or a promise that every tool already supports both formats.
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What changes when a repository uses SHA-256?
Git uses object identifiers to refer to blobs, trees, commits and tags. SHA-1 object names are 40 hexadecimal characters; SHA-256 names are 64. In a SHA-256 repository, commits, trees and tags that refer to other objects have different contents because those references change. Blobs do not refer to other objects.
Git’s hash-transition design describes a bidirectional mapping between SHA-1 and SHA-256 object names stored alongside object data. In that design, fetching from a SHA-1 server converts fetched objects into SHA-256 form and records the mapping; pushing to a SHA-1 server converts objects back to SHA-1 form. The mapping is generated locally and can be checked with git fsck. This is a compatibility mechanism, not a claim that one repository contains a mixture of SHA-1 and SHA-256 objects: intermixing the two formats in one repository is not a goal of the design.
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Compatibility is the main cost
Older Git versions cannot read SHA-256 repositories. Before adopting the format, identify the oldest Git client and every embedded Git implementation used by developers, CI, IDEs, hooks, build tools, hosting services and automation. A recent command-line Git on one machine is not enough if another part of the workflow cannot understand the repository.
The transition design also identifies protocol-related limitations. In particular, support for SHA-256 in the Git protocol is outside the initial design; shallow clones or fetches into SHA-256 repositories and some submodule-fetch behavior depend on that support. Check the behavior of the exact Git release and server you intend to use rather than assuming that the mapping makes every workflow compatible.
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What reftable changes
References are names such as branches and tags that point to objects. The existing files backend stores references using filesystem paths; reftable stores references and logs in a portable binary table format. The reftable specification supports both SHA-1 and SHA-256 identifiers, so adopting it does not by itself change the repository’s object format.
The Git project’s stated reasons for proposing reftable as the default include:
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- Reducing ref-name conflicts caused by filesystem case folding and Unicode normalization.
- Avoiding a full
packed-refsrewrite when references are deleted. - Supporting geometric compaction, atomic multi-reference transactions and more efficient writes of many references.
- Reducing storage through prefix compression.
These are format and design benefits, not guaranteed performance results for every repository. Their value depends on the repository’s size, ref count, workload and tooling. Examples or benchmarks in the format documentation should not be treated as universal promises.
Which choices fit your repository?
| Decision | What to weigh | Practical implication |
|---|---|---|
| Keep SHA-1 or use SHA-256 | Old-client compatibility, forge support, protocol-dependent workflows and embedded libraries. | Choose according to the least capable consumer in the workflow, not just the Git CLI on your workstation. |
Keep files or use reftable |
Worktree status, concurrent writers, implementation support, ref count and filesystem naming constraints. | Reftable may help with filesystem edge cases and large-ref-set costs, but migration has operational restrictions. |
| Migrate now or defer | Readiness of hosting and tooling, plus your ability to stage and roll back. | Git 3.0 has no planned date in the proposal, and existing SHA-1 repositories are not described as requiring conversion. |
How to plan a repository migration safely
Plan the two format changes independently. The documented migration command covers reference storage; it is not an object-format conversion command. The materials described here do not establish a general SHA-1-to-SHA-256 conversion procedure or a single command that safely converts every repository and workflow. Confirm the supported path for your Git build and integrations before attempting an object-format change.
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- Inventory the repository and consumers. Record
git --version, the repository’s object and ref-storage formats, registered worktrees, remotes, and every tool or service that reads or writes it. Check the installed Git documentation for how to inspect the formats; do not infer them from a successful command on one client. - Check compatibility end to end. Confirm support for the intended format in developer clients, servers and forges, libraries, CI, IDEs, hooks, submodules and repository-management tools. Ask vendors about the exact versions and workflows you use, then test representative clones and pushes in a staging repository. The Git project’s proposal makes ecosystem readiness a prerequisite; no provider-by-provider support matrix is established here.
- Back up and validate before changing ref storage. Make a recoverable backup and check that it can be restored. Pause repository writes and scheduled maintenance. The migration command cannot prevent concurrent writers, and concurrent changes may leave the migrated state inconsistent. Repositories registered for scheduled maintenance should be unregistered first.
- Migrate one dimension at a time. For ref storage, Git 2.46 release notes introduced migration from
filesto reftable. Current command documentation gives this synopsis:git refs migrate --ref-storage-format=<format> [--no-reflog] [--dry-run]. Confirm the exact option spelling and availability in the installed Git version before running it; documentation and release-note wording have differed. For a reftable dry run, use the installed version’s documented syntax with--dry-run, then perform the migration only after reviewing the result and blocking writes. Do not treat this command as a SHA-256 migration. - Verify the result and dependent workflows. Use
git refs verifyto check reference database consistency. For SHA-256 mapping and object consistency, Git documentsgit fsck. Also verify refs, reachability, remotes, CI, hooks, submodules and developer tooling in the actual workflow. - Keep a rollback route. Retain the validated backup and a way to restore or resume the previous workflow until all repository consumers have been confirmed to work.
Reftable migration limits to account for
- Repositories with worktrees cannot be migrated using the documented command.
- The command cannot lock out concurrent writes; stop writers externally before migration.
- Scheduled maintenance can write to the repository, so unregister the repository from scheduled maintenance before the operation.
What is known about tool support?
Git 2.45 release notes describe work to support repositories that work with both SHA-1 and SHA-256. Git 2.46 release notes add reference-storage migration and note CI interoperability testing for reftable written by JGit. Those milestones do not establish current support across every forge, library, IDE or automation tool, and the Git 3.0 proposal still treats ecosystem readiness as a prerequisite.
A libgit2 maintainer said in an October 4, 2024 discussion that SHA-256 support could be enabled with EXPERIMENTAL_SHA256, describing it as somewhat well tested but not battle-tested in a Git forge. That is historical, implementation-specific information—not a statement of current libgit2 status. Check the version and configuration you actually depend on.
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