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/aap/v1.1 -> .../v2.0)	minor or major
Documentation-only correction with no schema change	patch

The table above is the policy in force now that AAP has reached 1.0.0. During the pre-1.0 (0.x) series, a minor bump was allowed to carry breaking changes — per SemVer's 0.x allowance. v0.2 was exactly such a bump: it removed and renamed fields, flattened prices to integers, narrowed status to an enum, and dropped the separate contract manifest, all relative to v0.1. AAP v1.0.0 was the first stable release: its payload shape is the one introduced in v0.2, unchanged, riding A2A v1.0. AAP v1.1 is the current release; it dropped the optional HTTP+JSON (REST) binding, leaving JSON-RPC 2.0 as the single transport. 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/aap/v1.1) and the schema $id URLs (https://autoagentprotocol.org/v1.1/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-rest.yaml and https://autoagentprotocol.org/v0.1/openapi-jsonrpc.yaml do 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. v1.1).

How it is wired up today:

• Documentation: https://autoagentprotocol.org/docs/latest/<page> redirects (HTTP 200 client-side) to /docs/v1.1/<page> via the Docusaurus client-redirects plugin. Every page reachable under /docs/v1.1/ is also reachable under /docs/latest/. The frozen v0.1, v0.2, and v1.0 docs remain served at /docs/v0.1/<page>, /docs/v0.2/<page>, and /docs/v1.0/<page>.
• Schemas, examples, OpenAPI, MCP manifest: also served at https://autoagentprotocol.org/latest/... because the build pipeline mirrors static/v1.1/ into static/latest/. The frozen v0.1, v0.2, and v1.0 artifacts remain served at https://autoagentprotocol.org/v0.1/..., https://autoagentprotocol.org/v0.2/..., and https://autoagentprotocol.org/v1.0/....

URL form	Stability	Use case
https://autoagentprotocol.org/v1.1/...	Frozen	Production pinning.
https://autoagentprotocol.org/v1.0/...	Frozen (historical)	Production pinning for agents still on v1.0; still served.
https://autoagentprotocol.org/v0.2/...	Frozen (historical)	Production pinning for agents still on v0.2; still served.
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 v1.1)	Documentation browsing, not wire pinning.
https://autoagentprotocol.org/next/...	Reserved	The current docs/ is now v1.1; next will hold the preview of the next version once work on it begins.

Schema URL convention

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

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

Example for v1.1:

• https://autoagentprotocol.org/v1.1/schemas/inventory-search-request.schema.json
• https://autoagentprotocol.org/v1.1/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/aap/v1.1

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 versions in parallel during a transition. Each version is exposed by a separate extension URI on the agent card; a dealer that speaks both v1.0 and v1.1 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/v1.1/) and the Docusaurus current docs (docs/, served at /docs/v1.1/). 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/, spec/v0.2/, spec/v1.0/, versioned_docs/version-v0.1/, versioned_docs/version-v0.2/, versioned_docs/version-v1.0/) on every PR to prevent accidental modification.

What this means for buyer agents

• Pin to a specific version (https://autoagentprotocol.org/v1.1/) 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. During the pre-1.0 series a minor bump could change shapes (v0.2 removed fields, flattened prices, and narrowed status relative to v0.1); v1.0.0 kept the v0.2 payload shape unchanged riding A2A v1.0, and v1.1 dropped the optional HTTP+JSON binding so JSON-RPC 2.0 is the single transport. Speak the exact version a dealer advertises via its extension URI; a dealer that supports multiple versions declares each extension URI.

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/v1.1/); 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.