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OpenAI Assistants API shutdown: what to do now

Twelve months’ notice, a guided path for assistants, and nothing at all for thread history. What the 26 August shutdown means for teams still exposed.

What happened: 26 August 2026 · Written: 31 August 2026

The short answer

OpenAI switched off the Assistants API on 26 August 2026, twelve months after announcing it. Work moves to the Responses API and Conversations API. Assistants could be converted through the dashboard; conversation threads could not. If your application did not store its own messages, that history is gone. Check where your vendor keeps message data.

What actually happened

The OpenAI Assistants API stopped working on 26 August 2026. OpenAI’s migration guide now describes it in the past tense: officially sunset, no longer available. The notice was not short. Developers were told on 26 August 2025, a full twelve months ahead, and the deprecations table has carried the 2026-08-26 date since then, naming the Responses API and the Conversations API as replacements.

That is a reasonable runway, and OpenAI published a migration path rather than leaving developers to guess at one. The awkward part is what the runway did not cover. Migration was never a single switch, and the guide itself splits into two very different jobs: moving the assistant definitions across, and moving the conversation history. Only one of those ever had proper tooling behind it.

Threads were the hard part

Assistant objects had help. The dashboard offered a conversion that, in OpenAI’s words, would create a prompt object out of each existing assistant object. Threads had nothing equivalent. For conversation history, the guide’s instruction is to use messages already stored by your application, and it states plainly that the Assistants call which retrieved thread messages no longer works. There is no server-side route back to it.

So the shorthand doing the rounds, that there was no automated migration path, is right about threads and wrong about assistants. The distinction matters when you are assessing a vendor’s exposure. A team with only assistant configurations to move had a guided route. A team whose product value sat in stored conversation history depended entirely on whether it had been writing that history to its own database all along.

If it had not, the history is not retrievable now. New chats start on the Conversations API and the Responses API, and anything earlier comes from your own storage or does not come at all. That is a data-retention question rather than an engineering one, and it was settled months before the shutdown, by whichever architectural choice a team made when it first adopted threads.

The replacement is itself on a deprecation track

There is a further wrinkle worth naming, and it comes from OpenAI’s own migration guide rather than from commentary around it. Reusable prompt objects, the things assistants were converted into, are also being deprecated. The conversion that made the assistant side of this migration bearable produced artefacts that are themselves scheduled to go. No replacement date for them appears in the material we can verify.

Read carefully, that is a statement about pace rather than a warning about the Responses API. Responses and Conversations are the named destinations, and nothing on the deprecations page suggests otherwise. But anyone budgeting engineering time should assume this is not the last migration on this stack, and price in a second pass rather than treating the August work as finished.

What to do about it

If you buy software rather than build it, the useful question is not which API a vendor uses but where your conversation history physically lives. Ask whether the vendor stores message content in its own database or leaned on a provider’s thread store. Ask for the answer in writing. It determines whether the next provider deprecation is a vendor’s engineering sprint or your data loss.

If you build on this yourself and have not moved, the position is unchanged from any other shutdown: the endpoint is off, and no grace period is described anywhere in OpenAI’s documentation. Rebuild on the Conversations API and the Responses API, seed context from your own stored messages, and treat the absence of a thread export as a design lesson for the next provider.

What to do about it

Ask every vendor whose product runs on OpenAI where conversation history is stored: their database, or the provider’s. Get the answer in writing before you renew. If you build in-house, rebuild on the Conversations and Responses APIs now, seed context from your own message store, and budget a second migration, because the prompt objects assistants became are also being deprecated.

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Questions readers ask

When did the OpenAI Assistants API shut down?

On 26 August 2026. OpenAI notified developers a year earlier, on 26 August 2025, and listed the same removal date in its deprecations table throughout that twelve-month window. The migration guide now refers to the API in the past tense.

What replaces the OpenAI Assistants API?

The Responses API and the Conversations API. Both are named as replacements in OpenAI’s deprecations table, and OpenAI directs developers to its Assistants-to-Conversations migration guide for the details of moving an existing integration across.

Can I still recover my Assistants API thread history?

Not through OpenAI. The call that retrieved thread messages no longer works, and OpenAI’s guidance is to rebuild history from messages your own application stored. If your application never stored them, there is no supported way to get them back.

Where every figure came from

Each claim above was checked against a primary source, then checked again by a second reader who had not seen the first check. Open any of them and verify us.

  1. OpenAI notified developers of the Assistants API deprecation on 26 August 2025, with removal one year later on 26 August 2026 — confirming both the announcement date and the twelve-month notice period. developers.openai.com 2025-08-26
  2. The deprecations table lists the shutdown date 2026-08-26 for the Assistants API, with the Responses API and Conversations API named as its replacements. developers.openai.com 2026-08-26
  3. The deprecations page directs developers to the Assistants-to-Conversations migration guide for moving to the Responses API and Conversations API. developers.openai.com 2026-09-01
  4. The official migration guide confirms the shutdown already happened and that the API is gone — the page is written in the past tense as of today. developers.openai.com 2026-08-26
  5. There is no server-side migration for thread history: OpenAI tells developers to rebuild history from messages their own application stored, because the Assistants endpoint that read thread messages no longer works. This substantiates the ’no automated migration path for threads’ claim. developers.openai.com 2026-09-01
  6. For new chats, OpenAI instructs developers to start over on Conversations + Responses and to source any earlier history from their own storage. developers.openai.com 2026-09-01
  7. Nuance the story omits: assistants themselves DID have a dashboard-assisted conversion into prompt objects (unlike threads, which had none). This is a partial automated path on the assistant side only. developers.openai.com 2026-09-01
  8. Further nuance: the prompt objects that assistants were converted into are themselves now on a deprecation track, so the recommended migration target is partly unstable. developers.openai.com 2026-09-01
  9. OpenAI’s own announcement thread states the one-year sunset and points to a migration guide. community.openai.com 2025-08-26

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