01 · Operational consequence
Lifecyclecompleted
Severitycritical
ConsequenceThe Assistants API is no longer available on the OpenAI API. Calls that still depend on Assistants, Threads, Runs or Run Steps require migration to supported Responses-era primitives.
02 · Affected subjects
ComponentsAssistants API
AudienceDevelopers running production assistants on the deprecated Assistants API.
RegionOpenAI API; no regional exception documented
03 · Detection
Stable event IDksr-openai-assistants-api-2026-08-26
Change typemigration_deadline
04 · Before → after
BeforeDeprecated
AfterSunset
05 · Required action
ActionMigrate any remaining Assistants API integration now. Map Assistants to prompts or application configuration, Threads to Conversations, Runs to Responses and Run Steps to Items, then re-run tool, state, safety, latency and cost tests.
Replacement or migration pathMap Assistants to prompt or configuration structures, Threads to Conversations, Runs to Responses and Run Steps to Items. OpenAI does not provide an automated Threads-to-Conversations migration.
06 · Actionable date
Date roleMigration deadline
Date2026-08-26
Statuscompleted
07 · Kingy reproduction
StatusNot tested
LimitationsSource evidence reviewed; no paid vendor call or production reproduction was run.
08 · Sources and revision
Checked2026-09-04
Official sourceshttps://developers.openai.com/api/docs/deprecations · https://developers.openai.com/api/docs/assistants/migration · https://developers.openai.com/api/docs/guides/migrate-to-responses · https://developers.openai.com/api/docs/guides/conversation-state · https://developers.openai.com/api/docs/guides/function-calling
Correction history2026-08-27: Official post-sunset verification changed the record from an upcoming deadline to completed; OpenAI now says the Assistants API is no longer available.