Migrating from 3.0 to 3.1

A focused upgrade guide for moving AdCP 3.0 integrations to the 3.1 stable release.

Migrating from 3.0 to 3.1

3.1 is released. New 3.1 integrations should pin "3.1" after confirming the agent advertises it in supported_versions. Existing 3.0 integrations can remain pinned to "3.0" while they migrate.

3.1 is a minor release over 3.0. The protocol changes are additive: existing 3.0-conformant agents can remain on "3.0" without changing request or response shapes. Use this guide when you are preparing an SDK, buyer, seller, creative agent, signal agent, brand agent, or compliance workflow to claim or consume 3.1.

For the feature narrative, start with What’s New in AdCP 3.1. For the full release record, see Release Notes.

Upgrade checklist

Step	Who	Action
1	Everyone	Decide whether this integration is staying on "3.0" for now or moving to "3.1".
2	SDKs and hand-rolled clients	Add an adcp_version release pin on every request. Send "3.1" only to agents that advertise it.
3	Sellers and agents	Advertise every accepted release in get_adcp_capabilities.adcp.supported_versions and echo the served release at the envelope root.
4	Buyers	Decode VERSION_UNSUPPORTED and retry only against a version that the seller advertised.
5	Hand-rolled buyers	Add idempotency_key to read tasks as well as mutating tasks before claiming 3.1 behavior.
6	MCP and A2A adapters	Accept envelope fields and transport wrappers without rejecting unknown root members.
7	Error handlers	Treat error.code as an open string and dispatch on error.recovery when present.
8	Compliance operators	Run the 3.1 storyboard bundle and keep the 3.0 compatibility line green until the 3.1 badge is issued.

Version pinning

3.0 integrations negotiated by major version only. 3.1 adds release-precision negotiation:

• Use "3.0" for stable 3.0 traffic.
• Use "3.1" for stable 3.1 traffic after the agent advertises it.
• Do not send patch values such as "3.0.19" or full semver prereleases such as "3.1.0-rc.15" on the wire.

Sellers should reject unsupported pins with VERSION_UNSUPPORTED and include the supported release list in error.data.supported_versions. Buyers should not silently downshift across minor releases. Surface the mismatch or retry against a version the seller explicitly advertised.

Runtime changes to audit

Idempotency on every task

3.0 required idempotency_key on mutating requests. 3.1 extends the reliability model to every task so retries, replays, and downstream reconciliation behave uniformly. SDK users should pick up this behavior from the SDK release. Hand-rolled buyers should generate a UUID v4 idempotency key for read tasks as well as writes.

When a response is marked replayed: true, treat it as the historical result of the original operation. If you need fresh state before acting, re-read the relevant resource after handling the replayed response.

Envelope tolerance

3.1 relies on transport adapters tolerating the AdCP envelope root. MCP and A2A clients should unwrap the transport-specific wrapper first, then read AdCP fields such as status, result, errors, adcp_version, replayed, and context. Unknown envelope members must not cause rejection.

Error decoding

The standard error catalog expanded in 3.1, but error.code remains an open string. Clients should:

• Accept unknown error codes.
• Prefer error.recovery when present.
• Apply a bounded transient fallback for unknown legacy errors when error.recovery is absent.
• Handle the auth split between AUTH_MISSING and AUTH_INVALID.
• Treat CREDENTIAL_IN_ARGS as terminal and move credentials to the proper transport channel before retrying.

Proposal and action discovery cleanup

3.1 makes proposal_status the proposal source of truth and uses structured action discovery on products and buys. Sellers should not emit the pre-GA requires_proposal action mode. Buyers with cached prerelease action metadata should invalidate it and re-read the product, proposal, or buy surface.

Brand verification signing

Brand agents that implement verify_brand_claim or verify_brand_claims must return signed response evidence. Publish a per-brand response-signing key and bind signatures to the task, resolved brand tenant, responding agent URL, caller/request hash, and validity window.

Signal targeting

Signal identity moves toward SignalRef, with product-scoped included_signals, signal_targeting_options, and buy-time signal_targeting_groups. Owned-signal discovery and marketplace activation are separate capabilities. Buyers should call activate_signal only when the agent declares marketplace or activation support.

Creative formats and transformers

Creative agents should expose canonical format_kind values and discover build units through list_transformers. Format-attached input/output/pricing declarations are deprecated in favor of transformer-scoped configuration and pricing. Hosted audio/video slots should use duration_ms_exact for fixed durations and duration_ms_range for bounded or one-sided ranges.

Reporting and billing

3.1 adds delivery and usage finality markers, reach-window semantics, viewability.viewed_seconds, and the BILLING_OUT_OF_BAND error for creative billing outside AdCP. Buyers should avoid treating delivery numbers as final until the relevant finality fields say they are final.

Role-based migration

Role	Minimum prep before claiming 3.1
SDK buyer	Upgrade to an SDK that emits adcp_version, pins "3.1" when the seller supports it, adds idempotency keys consistently, and accepts open error codes.
Hand-rolled buyer	Add release pins, read-task idempotency keys, envelope tolerance, forward-compatible error decoding, and replay handling.
Seller	Advertise supported_versions, echo the served release, tolerate envelope fields, reject unsupported pins with VERSION_UNSUPPORTED, and audit idempotency/replay/error behavior.
Creative agent	Move discovery to list_transformers, publish canonical formats, and keep legacy format references only as compatibility aliases.
Signal agent	Separate owned-signal discovery from marketplace activation; expose product-scoped targeting options only where buyers can select them.
Brand agent	Publish response-signing keys and return signed evidence for brand verification tasks.
Compliance operator	Run 3.1 storyboards, retain 3.0 compatibility evidence, and issue version-scoped badges only for the release actually tested.

Prerelease artifacts

The 3.1 prerelease artifacts remain available for adopters who pinned them during validation, but new integrations should use the stable "3.1" wire value. If you built against a prerelease, invalidate cached prerelease-only fields such as requires_proposal, re-read current product/proposal/action metadata, and rerun the 3.1 storyboard bundle before claiming the stable release.

Related

• What’s New in AdCP 3.1
• Release Notes
• Versions & Compatibility
• Versioning & Governance
• Version Adaptation