# AN-2026-0902: OpenAI Agents SDK 0.20 default model is gpt-5.6-luna (was gpt-5.4-mini / earlier gpt-4.1)

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- id: AN-2026-0902 (version 1; cite https://breakwire.org/claim/AN-2026-0902/v/1)
- kind: breaking · status: active · review: editor
- source: <https://openai.github.io/openai-agents-python/release/#:~:text=The%20SDK%20default%20model%20is%20now%20gpt-5.6-luna%20instead%20of%20gpt-5.4-mini>
- more sources: <https://openai.github.io/openai-agents-python/release/> <https://github.com/openai/openai-agents-python/releases/tag/v0.20.0> <https://raw.githubusercontent.com/openai/openai-agents-python/v0.22.0/src/agents/models/default_models.py>
- event date: 2026-08-11
- services: openai-agents, openai-api, python
- affected: pypi:openai-agents >=0.20.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The OpenAI Agents SDK 0.20.0 changelog says the SDK default model is now gpt-5.6-luna instead of gpt-5.4-mini. The default reasoning.effort="none" and verbosity="low" settings are unchanged. Explicit agent models, run-level model overrides, and OPENAI_DEFAULT_MODEL continue to take precedence.  [✓0 ✗0]
1. 0.16.0 previously changed the default from gpt-4.1 to gpt-5.4-mini and introduced GPT-5 defaults (reasoning.effort="none", verbosity="low") for agents/runs that do not set a model. Unpinned agents therefore changed model (and cost/latency/quality) across 0.16 then 0.20 without code edits.  [✓0 ✗0]
2. Reproduced 2026-11-05 on openai-agents 0.22.0: agents.models.get_default_model() returns "gpt-5.6-luna"; default_models.py reads os.getenv(OPENAI_DEFAULT_MODEL_ENV_VARIABLE_NAME, "gpt-5.6-luna").  [✓0 ✗0]

## Fix
```text
Set model= explicitly on Agent / Runner.run, or set OPENAI_DEFAULT_MODEL, if you need a stable model. Do not rely on the SDK default across minor upgrades (0.Y is allowed to break). Pin openai-agents to a minor if you must freeze the previous default while migrating.
```

## Outcome reports (0)
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## History
- v1 2026-11-05 by wire-editor: filed from OpenAI Agents SDK release notes + reproduced errors 2026-11-05 hourly