OpenAI Assistants API calls to /v1/assistants, /v1/threads or runs started failing after August 26, 2026: what replaced it and how do I migrate?

Am I affected: OpenAI shut down the Assistants API on August 26, 2026, a year after announcing it on August 26, 2025. Code that still creates assistants, threads, messages or runs (/v1/assistants, /v1/threads, client.beta.assistants / client.beta.threads in the SDKs) now gets errors instead of responses. This includes third-party tools and no-code platforms that were built on Assistants. How to check: search your code and dependencies for 'beta.assistants', 'beta.threads', '/v1/assistants', '/v1/threads' and 'OpenAI-Beta: assistants'. Check request logs for failing calls to those paths. Fix: migrate to the Responses API plus the Conversations API, following OpenAI's Assistants migration guide. The rough mapping: - Assistant (instructions + tools + model) → a reusable Prompt, or simply the instructions/tools/model you pass on each Responses call - Thread → Conversation (server-side history), or pass previous_response_id to chain turns - Run → Response (one call, no polling loop: the result comes back directly or by streaming) - Run steps → output Items in the response File search, code interpreter and function calling are available as tools in Responses. Re-create vector stores and attach them to the file_search tool. Expect real code changes, not a string swap. Interim: there is no grace period, so the old endpoints won't come back. If a vendor tool broke, check for an update that targets Responses. Export any thread history you still need from your own database, since Assistants-side data can no longer be reached through the old API. After migrating: run your evals again. Responses and Assistants can differ in how tool calls are ordered and in default truncation of long conversations. Also check token usage, since sending full history on every turn costs more than a Conversation or previous_response_id. Sources: https://developers.openai.com/api/docs/deprecations https://developers.openai.com/api/docs/assistants/migration https://community.openai.com/t/assistants-api-beta-deprecation-august-26-2026-sunset/1354666