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This alpha V3 MCP contract is available only to enrolled Buyer Accounts. It adds discovery, connection setup, campaign-scoped session reads, durable session saves, and explicit generation or refinement for registered Creative Engines. The Creative Engines Page is available for enrolled Buyer Accounts. Provider qualification and the end-to-end buyer journey remain separate work.
Creative Engines gates generation and refinement, not assembly. Any authorized buyer can use the Creative Library to assemble a draft in a campaign Creative Session by choosing a format, filling slots, adding a name and click-through URL, and saving. This does not create a Creative. When Creative Engines is not enabled, the composer leaves those assembly controls available and asks your Apostra account team to enable it for the Buyer Account. When Creative Engines is enabled but the draft has no connected engine, the composer says generation needs a connected Creative Engine on the draft. Your Apostra account team enables Creative Engines for enrolled Buyer Accounts. Contact them to ask about enrollment. An engine is a creative service you can discover and connect. A connection is your authorization grant to that service. One engine can have several connections, each with its own credential and provider accounts.

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Open Creative Engines in Murph

In Murph, select Creative Engines in the Discover section of the Buyer navigation. The entry is shown only when Creative Engines is enabled for the active Buyer Account. It opens the same Page and does not grant access by itself. You can also ask Murph to find a registered provider and open its connection setup on the Page; you start the secure connection there.

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Discover an engine

Call search with kind: "creative_engine". Use query to match an engine or provider name, filter.ids for up to 50 exact engine IDs, and limit plus the returned cursor to page results. IDs are positive integer strings.
Results contain one record per engine, including its name, description, provider, authentication modes and your existing grants. The capabilities declaration lists modalities, transformer IDs, supported format IDs and build/preview support when the registered adapter supplies them. get with the same kind and an engine id returns one record. Declarations describe support; they are not a live provider health check or proof of access to every model. Grant status describes your connection state. pricing: null means this read has not obtained a quote, not that generation is free. The current supportedFormatIds are adapter format identifiers, not canonical AdCP format declarations or executable capability IDs. Discovery currently covers registered Creative Engines visible to the active buyer. Arbitrary external MCP endpoints cannot be added through this preview.

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Authorize and manage a connection

Use open_creative_engines_page to open the Creative Engines Page in an MCP Apps host. The Page has Connected and Available views. It separates declared capability from observed connection state and account access, and shows when no provider price has been quoted. It supports secure connection repair, account selection, advertiser mapping, and disconnect. It does not expose provider credentials, accept an arbitrary MCP URL, quote a price, or start generation. Pass connectionAction: "connect" with a registered engineId to focus that engine’s secure setup control. This opens no authorization handoff by itself: the buyer starts setup from the Page. Call save_connection with exactly one change. To begin authorization:
The result contains a secure authorization handoff. Open it to complete OAuth or enter a bearer credential, according to the engine’s supported modes. Never put a provider token into tool arguments. The tool does not return token values. The browser handoff identifies the registered provider. In the OpenAI customer-key form, it asks for an OpenAI API key and links to the official OpenAI API key dashboard. This is an explicit customer-key connection only; it does not configure a platform-managed credential or authorize generation spending. To list your creative grants:
Read a grant with get({"kind":"connection","id":"77"}). It includes safe credential status, selected account, advertiser mappings and a bounded account list. Use connectionAccountsOffset with the returned accountsPage.nextOffset for another account page. Provider metadata and secrets are omitted. Use the existing save_connection fields with connectionId to reconnect (authorization), refresh accounts (refreshAccounts: true), select a provider account (selectedAccountId), map an advertiser (advertiserMapping), or disconnect (state: "removed"). A connection cannot change its target. Disconnect retries remain available for owned grants after catalog delisting or preview enrollment is removed. Creative connections do not accept seller selection, advertiser activation, media billing, buying policy or Enhanced Reporting. Signup-restricted credentials cannot use the creative preview. AudioStack and ElevenLabs require an advertiser mapping before generation. This selects the provider organization or workspace that pays for the request. Use advertiserMapping: {state: "mapped", advertiserId: "42", accountId: "88"} with the connection ID. Read accountMappings to find the link ID for unmapping; use connectionMappingsOffset with accountMappingsPage.nextOffset for another mapping page. Replacing the provider key requires remapping the advertiser.

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Generation and funding

This alpha provides discovery, setup, session reads and the two Creative Session operations. save_creative_session saves a brief, selected output, approval or finalisation but never starts generation. generate_variants explicitly prepares and executes one saved session revision. These are generation operations and require Creative Engines. Keep the chosen engine, provider account and advertiser explicit when moving from setup into a session. A connection alone does not authorize spending. The operations do not provide a request estimate or turn an unknown catalog price into a quote. For accounts and clients with the existing V2 generation tools, use the generative creative workflow. Use the generation workflow’s applicable funding and price information before requesting paid work. The current catalog’s pricing: null cannot be used as a quote. Customer-key eligibility and provider account requirements still apply; see provider setup. A failed customer-key request does not authorize switching to a platform-funded request. During iteration, preserve the brief, reference assets, target format and parent variant. Retain returned session and task IDs so an interrupted request can resume without submitting another build. Review the exact output that will be finalized, then read back the saved creative. Content acceptance remains separate from seller review and campaign launch.

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Existing seller integrations

search({"kind":"connection"}) continues to list seller grants by default. Seller grants gain target: {kind: "seller", id: "..."} and retain sellerId. Existing save_connection calls using sellerId continue to work; new callers can use a seller target instead. Supplying conflicting fields fails validation. You can continue making creative directly with a provider and bring that creative into Apostra. This alpha does not change that workflow or start a generation job without an explicit generate_variants call.

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Read a creative session

A creative session holds work in progress: the brief, plan, variants, evaluation, selection and any finalized creative. Reading it does not start generation. List sessions within one campaign:
Use filter.status to choose drafting, refining, evaluating or finalized. The limit is at most 100. Results contain session IDs, campaign IDs, titles, statuses and revisions. When nextCursor is present, pass it as cursor with that same campaign and status filter. Each page reflects current state; the list does not promise a fixed snapshot or a total count. Text queries and other filters are not supported for sessions. Open a result with its campaign as sourceId:
The object includes its persisted revision, plan, variants and evaluation. The read returns the selected variant and the latest session history first. It does not return inline asset data. If a session has more history or detail than one tool response can carry, truncated: true and omitted identify the bounded fields; use the existing V2 workflow for the complete durable record. When the session has a saved engine connection, engine contains its engineId and connectionId. Credential material is not included. Hosted image, audio and video plans can identify their format with format_kind (image, audio_hosted or video_hosted) and params, without an agent URL. Image dimensions use params.width and params.height; an exact audio duration uses params.duration_ms_exact. The declared modality must match the selected engine. A canonical declaration cannot also specify a legacy target format. Explicit legacy format requests retain their existing compatibility path. When preparing image placement renders, the session uses each placement’s resolved dimensions. A placement without dimensions returns a warning instead of generating at the original image size. These renders still need the applicable seller compatibility checks before delivery. Session reads do not support include. Both reads require current access to the campaign and advertiser, and expired sessions are unavailable. save_creative_session saves a campaign brief and locked references, selects or approves one exact output, and finalises that approved output. Saving does not start generation. generate_variants is the separate explicit action for one saved revision. Reuse its actionKey only for an identical retry; name the parent output and feedback when refining. Both operations require the Creative Engines account capability and a saved engine connection. Generation can remain submitted or uncertain while its original task or receipt is recovered; it never silently submits a replacement request. Both operation responses include the current session, revision, and, when present, sessionGeneration. Generation also returns its actionId and each leaf’s status, task ID, and variant IDs; approval and finalisation controls remain in the session. Session detail is bounded in these responses. When sessionTruncated: true is present, sessionOmitted identifies omitted detail, while the returned action and retry controls remain exact. The durable session history is not paginated by these operations; use the existing V2 creative-session workflow to retrieve the complete record. If already-persisted action controls alone cannot fit in one response, the operation returns a bounded recovery error instead of clipping those IDs. Read the durable session before retrying the same saved action; this does not create a replacement generation request.