Costco

Costco Wholesale is a membership warehouse club with roughly 900 warehouses worldwide and the third largest retail revenue in the world. For a brand, Costco is a wholesale buyer, not a marketplace: a buyer selects your item, issues a purchase order, and you ship to a depot or, for Costco.com, direct to the member. There is no self-serve seller signup, no developer portal and no public API. Integration is classical X12 EDI, and for Costco.com dropship it is brokered through CommerceHub (now Rithum) rather than a Costco-run endpoint. The curated third-party storefront programme, Costco Next, was shut down in September 2026, which removes the one route that resembled a marketplace.

At a glance

What it is

Costco Wholesale operates membership warehouses in the United States, Canada, Mexico, the United Kingdom, Japan, Korea, Taiwan, Australia, Spain, France, Iceland, China, Sweden and New Zealand. The buying model is deliberately narrow: a typical warehouse carries around 4,000 active items against the 30,000 or more of a supermarket, so an item either wins a slot or does not exist. Buyers are organised by region and by food versus non-food, and Costco's own vendor inquiries page routes prospective suppliers to a regional division for food and sundries and to the Issaquah corporate office for everything else.

Three distinct commercial lanes matter to an integrator, and they behave differently:

1. Warehouse supply. You ship pallets to a Costco depot against a purchase order. This is the volume lane and the one EDI was built for.
2. Costco.com dropship. Orders placed on costco.com that ship from your warehouse to the member, with a Costco-branded packing slip. Tangentia's Costco.com integration sheet explicitly lists "branded packing slips for drop shipments" as a requirement.
3. Costco Next. A curated storefront programme launched in 2017 where Costco linked members through to a vendor's own site. It was shut down over the 2026 Labor Day weekend without a public explanation, and costconext.com now redirects to a Costco customer service answer stating that "Access to Costco Next store fronts is no longer available".

API access

There is no API access, in the sense the rest of this reference uses the term. Costco does not run a developer console, does not issue API keys to suppliers, and publishes no endpoint reference. The probes below were all run on 2026-09-21 and none resolved: supplier.costco.com, vendor.costco.com, b2b.costco.com, cwsupplier.costco.com, costcosupplier.com, marketplace.costco.com, seller.costco.com, edi.costco.com.

What does exist:

• Costco's vendor inquiries page, which is postal addresses and phone numbers by region, with no online application form. It links only to supplier diversity, the ethics hotline, human trafficking disclosure, logo requests and packaging graphics.
• Packaging and handling graphics standards, published as PDF, EPS and AI vector downloads, with packaging@costco.com as the contact. Large item packaging must carry standard pictograms in the upper left corner on all four sides and survive clamp pressures up to 2,500 psi and stacking to 25 feet.
• EDI trading partner specifications, which Costco distributes to selected suppliers rather than publishing. Every public description of them comes from an EDI provider who has implemented them.

For Costco.com specifically, Logicbroker's integration guide states that onboarding begins by engaging "Costco.com via CommerceHub (their EDI processor)", then configuring sender and receiver IDs with an EDI qualifier and identifier, establishing staging and production connections, mapping documents and running certified test cases. That makes CommerceHub, now trading as Rithum, the practical counterparty for the dropship lane. If you already have a CommerceHub connection for another retailer, the Costco.com lane is an additional trading relationship on infrastructure you have, not a new build.

Authentication

There is no token exchange to implement. EDI identity is structural and is agreed once, out of band, during onboarding:

1. Costco or its EDI processor issues you an interchange qualifier and interchange ID, the ISA05/ISA06 and ISA07/ISA08 pairs, which identify sender and receiver on every envelope.
2. A transport is chosen. The providers surveyed all offer the same three: AS2 as a direct encrypted internet connection, SFTP or FTP for batch, and a VAN. Logicbroker recommends "AS2 of SFTP protocol to eliminate VAN charges".
3. For AS2, you exchange X.509 certificates and AS2 identifiers, and configure signed MDN receipts. For SFTP, you exchange an SSH key pair and directory paths. Credentials are per trading relationship, not per application.
4. A staging connection is established and test documents are exchanged until Costco or the processor certifies the mapping. Only then is production enabled.
5. Every document you receive is acknowledged with a 997 functional acknowledgement, and every document you send should expect one back. The 997 is the closest thing EDI has to an HTTP status code and is the primary signal that a transmission was structurally accepted.

The standard in force is ANSI ASC X12 version 4010 according to the Crstl requirements guide. TrueCommerce's Costco page states that its Costco codes follow EDIFACT with X12 and XML also supported, which reflects TrueCommerce's own European product framing rather than a Costco requirement. Treat X12 4010 as the working assumption and confirm the version on the specification Costco sends you, since 4010 is old enough that some retailers have moved parts of their stack forward.

A credential store for Costco therefore holds no access tokens and no refresh job. It holds an AS2 certificate with an expiry date, or an SSH key, plus the qualifier and ID pair. The only recurring operational task is rotating the AS2 certificate before it expires, which is a calendar item rather than a runtime concern.

Objects we can read

Field-level schemas are not published by Costco, so no sample document is reproduced here. What follows is the transaction set list as corroborated by Tangentia, Cleo, Logicbroker and Crstl, with the object each maps to.

Orders

EDI 850 Purchase Order, inbound to the supplier. This is the order. It carries the Costco purchase order number, ship-to location, requested delivery window, line items by UPC or GTIN with quantity and agreed cost.

EDI 860 Purchase Order Change, inbound. Amendments to a live purchase order. Treat as a replace against the original PO number rather than a delta.

EDI 855 Purchase Order Acknowledgment, outbound. Your confirmation, with line level accept, reject or quantity change.

EDI 870 Order Status Report, listed by Tangentia for Costco.com. Order status back to Costco.

Order items

Not a separate transaction. Order items are the line item loop inside the 850, keyed by the Costco item number and the UPC or GTIN. There is no independent item identifier you can query.

Products and listings

EDI 832 Price/Sales Catalog. Crstl describes it as "product and pricing updates" and Tangentia lists it as "Product Catalog" for Costco.com. This is the nearest thing to a listing write, and it is a catalogue feed, not a listing record. There is no endpoint that returns your current live items and no notion of listing status, listing URL or listing id that a connector could read back.

Inventory

EDI 846 Inventory Inquiry/Advice. Cleo lists it as inbound to the supplier and Logicbroker lists it as inbound too, which is unusual: for most dropship retailers the 846 goes supplier to retailer to declare available stock. Both directions appear in the sources and they do not agree on which Costco uses. Assume the dropship direction, supplier to Costco, and confirm during onboarding.

Shipments and tracking

EDI 856 Advance Ship Notice, outbound, and the document that matters most. It declares shipment contents, packaging hierarchy, carrier and tracking before the goods arrive. Every carton carries a GS1-128 label whose SSCC-18 serial shipping container code is embedded in the 856, which is what links the physical carton to the electronic record. Crstl reports that the ASN "generates more chargebacks than any other document" and must be transmitted before physical arrival, ideally within hours of despatch.

Returns and cancellations

No dedicated transaction set appears in any source. Returns are handled through Costco's member-facing returns process and reconciled commercially. EDI 864 Text Message carries unstructured communications and is the channel through which exception traffic tends to arrive.

Payments and settlements

EDI 810 Invoice, outbound, and EDI 820 Payment Order/Remittance Advice, inbound. Crstl describes Costco's three way match: the 850, the 856 and the 810 are compared automatically, perfect alignment triggers payment, and mismatches create chargebacks. The 820 is the settlement record to load.

Customers

For warehouse supply, none. Costco does not share member identity with suppliers. For Costco.com dropship the 850 carries a ship-to name and address so the parcel can be delivered, which is PII and should be stored as such, but there is no customer object, no stable customer id and no email.

Locations

Ship-to warehouse and depot identifiers appear on the 850 and on the GS1-128 carton label. There is no location directory transaction to enumerate them; you learn the codes from the orders you receive.

Sell-through

EDI 852 Product Activity Data, listed by Tangentia for Costco.com. Where Costco sends it, this is point of sale and on-hand movement by item and location, and it is the most commercially valuable document Costco transmits. It has no equivalent in the unified model as defined and is worth storing raw.

Writing back: listings, price and stock

Not in any form a connector would recognise, and this is the single most important thing to understand about Costco.

• There is no listing object. Costco creates the item record itself from the specification you supply during item setup, and the member-facing page on costco.com is built by Costco.
• You do not control price. Costco sets the member price from your agreed cost and its own margin rules. The 832 catalogue feed communicates your cost and product data; it is not a price control surface.
• Stock is communicable via the 846 for the dropship lane, so availability is the one field that behaves like a normal write. For warehouse supply, stock is irrelevant: Costco owns the inventory once it is received.
• Activate and deactivate do not exist. An item is discontinued by the buyer, not by a supplier call.

The manual route is the same as the automated one: the item setup spreadsheet and specification pack that Costco's buying office sends you. There is no bulk upload template in a seller panel because there is no seller panel.

Webhooks and notifications

None. EDI is polled or scheduled exchange. Practical cadence:

• Poll the AS2 or SFTP inbox for new 850 and 860 documents every 15 minutes during business hours. Costco purchase orders are not high frequency but the ASN deadline is tight enough that an hour of latency at the front of the process is an hour you cannot spend at the back.
• Send the 855 within the window stated on your specification, commonly 24 hours.
• Send the 856 within hours of despatch and before arrival. This is the one hard deadline.
• Poll for 820 remittance daily.
• Reconcile 997 acknowledgements continuously. A missing 997 means the document did not land and is the failure you want alerting on.

Rate limits and pagination

Not applicable in the API sense. There are no request quotas, no rate limit headers and no pagination. The operational constraints are file size limits and transmission windows agreed with the VAN or set by the AS2 endpoint, plus batching conventions on your specification. The limit that actually bites is the chargeback schedule, since Costco enforces compliance financially rather than by rejecting traffic.

Crstl's published chargeback figures, quoted as of 2026, are: ASN errors or late submission 50 to 200 US dollars per incident; label mismatches 50 to 150 dollars per carton; data discrepancies across the 850, 856 and 810 at 1 to 3 percent of purchase order value; quantity variances at 1 to 5 percent of affected items; late document transmission 100 to 200 dollars per incident. These come from a vendor blog rather than from Costco and should be confirmed against your own agreement, but the shape is consistent with how Costco is described across all sources: document accuracy is a cost line, not a quality metric.

Mapping to the unified model

Gaps and open questions

• Direction of the 846. Cleo and Logicbroker both list it inbound to the supplier, which contradicts the usual dropship pattern. One of the two framings is wrong and only the Costco specification settles it.
• Whether Costco.com dropship always goes through CommerceHub. Only Logicbroker states this explicitly. Tangentia and Cleo describe direct Costco.com EDI without naming an intermediary. It is possible both routes exist depending on when the supplier was onboarded.
• X12 version. 4010 per Crstl, EDIFACT per TrueCommerce's framing. Unresolved from public sources.
• Costco Canada, UK and Japan. All three are separate trading entities with their own buying offices and, very likely, their own EDI specifications and item numbering. Nothing public describes whether a supplier's US mapping carries over. Assume it does not.
• Whether anything replaces Costco Next. Nothing announced as of 2026-09-21. If Costco relaunches a third-party surface, it would be the first plausible candidate for a real seller API and this page should be revisited.
• 852 availability. Tangentia lists it for Costco.com but no source states whether it is offered to all suppliers or negotiated. It is worth asking for explicitly, since it is the only sell-through visibility on offer.

Sources

• Costco vendor inquiries, the official supplier entry point: costco.com/f/-/vendor-inquiries
• Costco packaging and handling graphics standards: costco.com/packaging-handling-graphics.html
• Costco customer service answer on Costco Next, confirming the storefronts are closed, which is where costconext.com now redirects: customerservice.costco.com answer 1020039
• EcomCrew on the Costco Next shutdown over Labor Day weekend 2026 and the fiscal Q3 2025 earnings call remarks: ecomcrew.com
• Logicbroker Costco.com EDI integration, the source for CommerceHub as the EDI processor and for the AS2 or SFTP recommendation: logicbroker.com
• Cleo trading partner network, Costco.com, for the 846, 850 and 856 list: cleo.com
• Tangentia Costco.com EDI integration, the fullest transaction set list including 832, 852, 864 and 870: tangentia.com
• Crstl Costco EDI requirements, for X12 4010, the GS1-128 and SSCC-18 linkage, the three way match and the chargeback schedule: crstl.ai
• TrueCommerce Costco trading partner page, which states EDIFACT with X12 and XML also supported: truecommerce.com
• DNS and HTTP probes on 2026-09-21 for supplier.costco.com, vendor.costco.com, b2b.costco.com, cwsupplier.costco.com, costcosupplier.com, marketplace.costco.com, seller.costco.com and edi.costco.com, none of which resolved