Versioning

Auto Agent Protocol uses Semantic Versioning (SemVer) for the published specification, schemas, and contract identifiers. The rules below are normative.

SemVer policy

Each released version of AAP has a major.minor version number (v0.1, v0.2, v1.0, v1.1, ...). The patch level is reserved for documentation-only fixes that do not change schemas, examples, or required behavior.

Change	Version bump
Adding a new optional field to an existing request or response schema	minor
Adding a new skill	minor
Adding a new optional behavior rule (SHOULD, MAY)	minor
Adding a new error code	minor
Removing a field, renaming a field, tightening a type, narrowing an enum	major
Changing a required field's semantics	major
Changing the agent-card extension URI (e.g. extensions/a2a-automotive-retail/v0.1 -> .../v0.2)	major
Documentation-only correction with no schema change	patch

The table above describes the policy once AAP reaches 1.0. While AAP is pre-1.0 (the 0.x series), a minor bump MAY carry breaking changes — per SemVer's 0.x allowance. v0.2 is exactly such a bump: it removes and renames fields, flattens prices to integers, narrows status to an enum, and drops the separate contract manifest, all relative to v0.1. Pin to the exact version a dealer advertises.

The AAP version lives in exactly one place on the wire: the agent-card extension URI (e.g. https://autoagentprotocol.org/extensions/a2a-automotive-retail/v0.2) and the schema $id URLs (https://autoagentprotocol.org/v0.2/schemas/...). Per-message data.type and mediaType are intentionally version-free; the dealer's agent-card pins the active version once per session.

Released versions are immutable

Once an AAP version is published at a stable URL (e.g. https://autoagentprotocol.org/v0.1/), the schemas, examples, and OpenAPI artifacts at that URL are frozen forever. Dealers and buyer agents that pin to v0.1 can rely on the schemas not changing under them.

Concretely:

• https://autoagentprotocol.org/v0.1/schemas/<file>.schema.json does not change after release.
• https://autoagentprotocol.org/v0.1/openapi.yaml does not change after release.
• The set of data.type identifiers defined in v0.1 (e.g. inventory.search.request, lead.submit.response) does not grow or change.
• Documentation prose at https://autoagentprotocol.org/docs/v0.1/ MAY receive editorial fixes, but cannot change normative content.

The latest alias

The path https://autoagentprotocol.org/latest/ always aliases the highest released version. It is intended for browsing convenience, not for production wire pinning. Production agents SHOULD pin to a specific version (e.g. v0.2).

How it is wired up today:

• Documentation: https://autoagentprotocol.org/docs/latest/<page> redirects (HTTP 200 client-side) to /docs/v0.2/<page> via the Docusaurus client-redirects plugin. Every page reachable under /docs/v0.2/ is also reachable under /docs/latest/. The frozen v0.1 docs remain served at /docs/v0.1/<page>.
• Schemas, examples, OpenAPI, MCP manifest: also served at https://autoagentprotocol.org/latest/... because the build pipeline mirrors static/v0.2/ into static/latest/. The frozen v0.1 artifacts remain served at https://autoagentprotocol.org/v0.1/....

URL form	Stability	Use case
https://autoagentprotocol.org/v0.2/...	Frozen	Production pinning.
https://autoagentprotocol.org/v0.1/...	Frozen (historical)	Production pinning for agents still on v0.1; still served.
https://autoagentprotocol.org/latest/...	Tracks the highest released version (now v0.2)	Documentation browsing, not wire pinning.
https://autoagentprotocol.org/next/...	Reserved	The current docs/ is now v0.2; next will hold the next-version preview once v0.2 is cut as a release.

Schema URL convention

Every AAP JSON Schema lives at a version-pinned URL:

https://autoagentprotocol.org/v{version}/schemas/{filename}

Example for v0.2:

• https://autoagentprotocol.org/v0.2/schemas/inventory-search-request.schema.json
• https://autoagentprotocol.org/v0.2/schemas/vehicle.schema.json

The $id inside each schema file matches its public URL. Schema cross-references ($ref) use relative paths within the same version directory.

The AAP version is announced only via the agent-card extension URI and the schema $id URLs. There is no separate contract document; a buyer agent reads the extension URI to learn the version and then validates against the version-pinned schema URLs published by AAP.

Extension URI

The A2A extension URI is version-pinned per major.minor:

https://autoagentprotocol.org/extensions/a2a-automotive-retail/v0.2

A future minor version introduces a new extension URI. Dealer agents that support multiple AAP minor versions MAY declare multiple extension entries on their A2A agent card; buyer agents pick the highest version they understand.

Side-by-side versioning

Dealer agents MAY run multiple AAP minor versions in parallel during a transition. Each version is exposed by a separate extension URI on the agent card; a dealer that speaks both v0.1 and v0.2 declares both extension URIs on its single agent card, and buyer agents pick the highest version they understand.

Release process

Each AAP release goes through three stages:

1. Current (working) — in-flight work lives in the current version directory (spec/v0.2/) and the Docusaurus current docs (docs/, served at /docs/v0.2/). Schemas and prose may change while the version is unreleased.
2. v{version} (release candidate) — schemas are frozen, prose may receive editorial polish.
3. v{version} (released) — schemas, prose, examples, and OpenAPI are immutable. The latest alias is updated to point here, and the docs are snapshotted into versioned_docs/version-v{version}/.

The repository runs a freeze-check tool over released directories (spec/v0.1/, versioned_docs/version-v0.1/) on every PR to prevent accidental modification.

What this means for buyer agents

• Pin to a specific version (https://autoagentprotocol.org/v0.2/) in production.
• Read the agent-card extension URI to learn the AAP version the dealer agent speaks.
• Validate against the version-pinned schema URLs published by AAP — those URLs are version-pinned.
• Do NOT assume cross-version compatibility. While AAP is pre-1.0, a minor bump MAY change shapes (v0.2 removes fields, flattens prices, and narrows status relative to v0.1). Speak the exact version a dealer advertises via its extension URI; a dealer that supports both declares both extension URIs.

What this means for dealer agents

• Once you publish, freeze. Do not edit released schemas in place.
• Develop changes against the current version directory (spec/v0.2/); cut them into a new version directory when you release.
• Bump the version (and the agent-card extension URI's v{major}.{minor} suffix) for any breaking change.
• Maintain the latest alias on your documentation host so casual browsers always land on the most recent published version.