As of August 5, 2026, v3 is the current contract for the OPDC API. It is a full rewrite of the request and response shapes around one idea: everything an integrator needs to know should be visible in the status code, the envelope, or the error body.
v3 ships beside v2, not instead of it. Nothing you have running today stops working.
What changed
The whole surface is two shapes plus a list of nouns: one read envelope, one write envelope, and one error body.
A business failure is a 4xx or a 5xx, so res.ok is a correct check and every HTTP client, proxy, and retry library already understands the answer.
application/problem+json on every status, with a stable machine-matchable code you can branch on. One parser handles every failure your client will ever see.
Every query returns asOf, page, and data. Every write returns the document plus its journal, job costs, and inventory movements under the same keys.
Retry a timed-out post with the same key and get the original response back, so a flaky connection cannot turn one invoice into two.
Add dryRun=true to execute the whole cascade against live data inside a transaction that is rolled back, and see exactly what would have posted.
Requests are checked against the contract before they run. A misspelled field comes back as a 400 that names it, so you find the typo in development instead of in a report.
If you are on v2
/api/v2 stays available as a frozen compatibility surface. It is not being deleted out from under you, so no existing integration has to move to keep working.
v2 is scheduled for removal in December 2026. New integrations should start on v3, and existing ones have time to migrate deliberately.
/api/v3/{entity}/query and use the v3 resource name. page.count to page.totalCount. v3 page numbers start at 1. X-Correlation-Id. The full migration checklist, with request and response examples for every step, lives in the v3 guide.
Where to start
Thirteen domains are documented, each with its own OpenAPI document you can load into your client generator.
Getting started, entities, filters, writes, and errors, with copyable examples in curl, Python, and JavaScript.
The complete v3 contract, machine readable. This is the contract itself, not a description of it.
Tell us what your v2 client does today and we will map it to v3 endpoints with you.
Book a call and we will run v3 queries against a copy of your Sage company, so you can see exactly what comes back.