OpenAI Shuts Down the Assistants API: What Changed on August 26, 2026 and What Retires Next

On August 26, 2026, OpenAI switched off the Assistants API. Any product that still called it on that date stopped getting answers from it. The removal was not a surprise: OpenAI's deprecations page records that developers were notified on August 26, 2025, exactly one year earlier. Even so, a year is easy to lose when a feature works and nobody on the team is watching a vendor's changelog.

If your company commissioned a chatbot, support assistant or document tool between 2023 and 2025, there is a fair chance it was built on this API. Whoever maintains your custom software and web applications should be able to tell you in a few minutes whether you were affected, and whether you are exposed to the next round of retirements.

That next round matters as much as the shutdown itself. OpenAI has announced three more end dates between October 31, 2026 and February 26, 2027, and one of them complicates the official migration route away from Assistants.

What OpenAI shut down on August 26, 2026

The Assistants API was OpenAI's earlier way to build an assistant that kept a conversation going, called tools and searched files. A developer created an "assistant" (the configuration), opened a "thread" (the conversation) and started a "run" (the model working on the latest message). The OpenAI API changelog entry for August 26, 2026 states that the Assistants API shut down on that date and tells developers to migrate to the Responses API and Conversations API.

OpenAI's deprecations page defines its terms plainly: a deprecated product is on its way out but still works, while a shutdown or sunset means the model or endpoint is no longer accessible. The Assistants API is now in the second category. This is a released, completed change, not a future plan.

What replaces the Assistants API

OpenAI's Assistants migration guide maps the old building blocks to new ones. Threads become conversations, which can hold messages, tool calls and tool outputs. Runs become responses. Run steps become items. The guide describes the Responses API as doing away with the polling loop the Assistants API needed, where an application had to keep asking whether a run had finished.

Two points in that guide deserve a manager's attention. First, as we read it, nothing is migrated automatically: the guide supplies example code for copying thread history into conversation items, and the work is left to the developer. Second, the guide told teams to move stored history before the sunset date. If your team did not do that, ask them directly what conversation history your product still holds and where it lives.

The catch: reusable prompts are being retired too

The same migration guide maps the old "assistant" object to a "prompt", a saved configuration of model, instructions and tools managed in the OpenAI dashboard. However, the deprecations page shows that on June 3, 2026 OpenAI announced the retirement of reusable prompt objects and the v1/prompts API, with shutdown scheduled for November 30, 2026. Its advice there is to move reusable prompt content into your own application code.

In practice this means a team that followed the migration guide to the letter may have moved from one retiring feature onto another. If your developers migrated off Assistants in the last year, ask whether the result depends on dashboard prompt objects. If it does, there is a second, smaller migration to finish before the end of November.

More shutdown dates on the calendar

These are announced future dates taken from OpenAI's deprecations page and changelog. None of them has taken effect yet as of October 4, 2026, and OpenAI can revise its schedule, so check the page before you plan around them.

• October 31, 2026: existing evals on OpenAI's Evals platform become read-only.
• November 30, 2026: Agent Builder, the Evals platform (dashboard and API) and reusable prompts are scheduled to shut down. OpenAI notes that ChatKit remains available.
• February 26, 2027: the transcription models whisper-1, gpt-4o-transcribe, gpt-4o-mini-transcribe and gpt-4o-transcribe-diarize are scheduled for removal. This was announced on August 26, 2026, and the listed replacements are gpt-transcribe and gpt-live-transcribe.

The transcription date is the one most likely to catch non-AI products. Whisper has been wired into call recording tools, meeting note features, voicemail-to-text and voice search for years, often by a developer who has since moved on.

What this means for your business

What follows is our reading of the situation, not a statement from OpenAI.

The first lesson is about ownership. A feature built on a hosted AI service is not finished when it launches. It carries a maintenance obligation that follows the vendor's timetable, not yours. One year of notice is generous by industry standards, and products still broke on August 26 because nobody was assigned to read the notices.

The second is about how failures show up. When an API endpoint is removed, the usual symptom is not a clear error message for the customer. It is a chat window that spins, a support form that silently drops messages, or an internal tool that returns blanks. If you have an AI feature that has gone quiet since late August and usage is low enough that nobody complained, this may be the reason.

The third is contractual. If an outside agency or freelancer built the feature, check whether your agreement covers vendor-driven changes like this one. Many fixed-price builds do not, which leaves the client to discover the problem and pay for the fix. For US and UK buyers alike, this is worth settling in the support terms before the next deadline. Our guide to outsourcing software development from the US and UK covers what to ask for in a maintenance clause.

What to do next

None of this requires a rebuild. It requires an inventory and a short plan.

• Ask your developers to search the codebase for calls to assistants, threads and runs, and for the model names whisper-1 and gpt-4o-transcribe.
• Check the OpenAI usage dashboard for any traffic to deprecated models or endpoints, including from staging systems and forgotten scripts.
• If you use dashboard prompt objects, Agent Builder workflows or the Evals platform, export what you need and schedule the move before November 30, 2026.
• Name one person who owns vendor deprecation notices and put OpenAI's deprecations page on a monthly review.

When the migration work is planned, treat it as a chance to test, not just to swap endpoints. A newer model or API can answer the same question differently. Run your real prompts and a sample of real customer questions through the new setup, compare the answers, and check cost per request before you switch production traffic. With the Evals platform itself on the retirement list, that comparison needs to live in a test suite your own team controls.

Conclusion

OpenAI removed the Assistants API on August 26, 2026, after a year of notice, and its documented replacements are the Responses API and Conversations API. Reusable prompts, Agent Builder and the Evals platform are scheduled to follow on November 30, 2026, and four older transcription models on February 26, 2027. The practical task for a business is to find out which of these it depends on and to get the changes scheduled while there is still time to test them.

If you are not sure what your product calls behind the scenes, or you need help moving an older assistant onto current APIs, you can contact Entrant Technologies to talk through an audit and migration plan.