# OpenAI Assistants API Responses API migration deprecation threads runs

Status: search-observed
Product: OpenAI API
Last verified: 2026-06-25
Canonical HTML: https://gitdocs.org/fix/openai-assistants-api-responses-api-migration-deprecation-threads-runs
Machine JSON: https://gitdocs.org/api/fixes/openai-assistants-api-responses-api-migration-deprecation-threads-runs.json

## Exact Symptom

See the observed Codex queries below.

## Diagnosis

SDK types may still accept fields that the selected hosted model rejects; model retirement, tokenizer, thinking, and tool behavior are external and fast-moving.

## Fix

```
Verifier checks current model ID, accepted payload, structured output/tool parsing, and behavior under retries.
```

## Avoid

- Changing local code without checking the current external contract.
- Retrying the same install, build, or API call with no version/source change.
- Applying a broad unsafe bypass when a narrow compatibility fix is available.

## Observed Codex Queries

- site:platform.openai.com/docs Assistants API deprecation Responses API migrate threads runs official OpenAI
- OpenAI Assistants API Responses API migration deprecation threads runs
- https://platform.openai.com/docs/assistants/migration
- 'Assistants API is deprecated' in https://platform.openai.com/docs/assistants/migration

## Sources

- OpenAI new tools for building agents: https://openai.com/index/new-tools-for-building-agents/
- Official reference opened by Codex: https://platform.openai.com/docs/assistants/migration