Specification Stages and Versioning

Specification Stages

Specifications go through various stages of development from which you should have different expectations. This document defines the different stages the SLSA project uses and their meaning for readers and contributors.

Every specification page should prominently display a Status section stating which stage the specification is in with a link to its definition.


This is the first stage of development a specification goes through. At this point, not much should be expected of it. The specification may be very incomplete and may change at any time and even be abandoned. It is therefore not suitable for reference or for implementation beyond experimentation.

A specification may be published several times during this stage as work progresses. The status section of the document may provide additional information as to its development status and whether reviews and feedback are welcome.

See the Governance for other considerations related to a Draft Specification.


At this stage the document is considered to be feature complete and is published as a way to invite final reviews. Editorial changes may still be made but no addition of new features is expected and short of problems being found no significant changes are expected to happen anymore.

See the Governance for other considerations related to a Candidate for Approved Specification.


At this stage the document is considered stable. No changes that would constitute a significant departure from the existing specification are expected although changes to address ambiguities and edge cases may still occur.

See the Governance for other considerations related to an Approved Specification.


This stage indicates that the specification is no longer maintained. It has been either rendered obsolete by a newer version or abandoned for some reason. The status of the document may provide additional information and point to the new document to use instead if there is one.


SLSA needs revision from time to time, so we version the specification to facilitate conformance efforts and prevent confusion. We assign a single version number to the Core Specification and Attestation Formats, collectively known as the SLSA Specification.

Given a version MAJOR.MINOR, we will increment

  • MAJOR version when making backwards incompatible changes to an Attestation Format or adding new requirements to an existing level in the Core Specification.
  • MINOR version when adding new tracks or levels to the Core Specification, modifying an existing level without fundamentally changing its meaning, or adding new fields to an Attestation Format in a backwards-compatible way. For more details on Attestation Format versioning, see the in-toto Versioning Rules.

Although we can revise the contents of level, we will never change a level’s high-level meaning after publication (e.g. SLSA Build Level 2 will retain its general meaning between major versions). If you require precision when referring to SLSA levels, then include their version number using the syntax SLSA [Track] [Level] ([Version]) (e.g. SLSA Build L3 (v1.0)). For more details on SLSA versioning, see the SLSA v1.0 Proposal.