SLSA

SLSA (Supply-chain Levels for Software Artifacts, pronounced “salsa”) is a security framework that defines progressive levels for hardening how software is built and released. Originating at Google and now stewarded under the OpenSSF, it gives teams a common language for describing how tamper-resistant a build pipeline is and what evidence backs that claim. The point is to make the path from source to published artifact verifiable, not just trusted.

• Progressive levels - A tiered model (roughly Build L1 through L3) where each level demands stronger guarantees against tampering.
• Provenance attestations - Signed, machine-readable metadata describing exactly how, where, and from what an artifact was built.
• Build integrity - Requirements for isolated, scripted builds that resist a single compromised developer or workstation.
• Ecosystem-neutral - A framework meant to layer onto existing CI/CD systems rather than replace them.

For APIs, SLSA is most relevant to the packages, containers, and gateway components that make up an API platform, where a compromised build is a direct path to a compromised production surface. Provenance attestations fit naturally alongside other supply-chain signals in governance — the same instinct behind security.txt and SBOM adoption — as machine-checkable evidence of operational maturity. As build and release pipelines increasingly involve automated agents, verifiable provenance becomes the way to trust what those pipelines produce.