use-cases/api-integration-migrations.md Codex Docs, 2026-03-07 00:33 UTC → 2026-03-31 06:35 UTC

1# Upgrade your API integration | Codex use cases

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3[← All use cases](https://developers.openai.com/codex/use-cases)

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5Use Codex to update your existing OpenAI API integration to the latest recommended models and API features, while checking for regressions before you ship.

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7Intermediate

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91h

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11Related links

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13[Latest model guide](https://developers.openai.com/api/docs/guides/latest-model) [Prompt guidance](https://developers.openai.com/api/docs/guides/prompt-guidance) [OpenAI Docs MCP](/learn/docs-mcp) [Evals guide](https://developers.openai.com/api/docs/guides/evals)

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15## Best for

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17 - Teams upgrading from older models or API surfaces

18 - Repos that need behavior-preserving migrations with explicit validation

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20## Skills & Plugins

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22- [OpenAI Docs](https://github.com/openai/skills/tree/main/skills/.curated/openai-docs)

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24 Pull the current model, migration, and API guidance before Codex makes edits to your implementation.

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26## Starter prompt

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28Use $openai-docs to upgrade this OpenAI integration to the latest recommended model and API features.

29Specifically, look for the latest model and prompt guidance for this specific model.

30 Requirements:

31- Start by inventorying the current models, endpoints, and tool assumptions in the repo.

32- Identify the smallest migration plan that gets us onto the latest supported path.

33 - Preserve behavior unless a change is required by the new API or model.

34 - Update prompts using the latest model prompt guidance.

35- Call out any prompt, tool, or response-shape changes we need to review manually.

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37## Introduction

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39As we release new models and API features, we recommend upgrading your integration to benefit from the latest improvements.

40Changing from one model to another is often not as simple as just updating the model name.

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42There might be changes to the API–for example, for the GPT-5.4 model, we added a new `phase` parameter to the assistant message that is important to include in your integration–but most importantly, model behavior can be different and require changes to your existing prompts.

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44When migrating to a new model, you should make sure to not only make the necessary code changes, but also evaluate the impact on your workflows.

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46## Leverage the OpenAI Docs skill

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48All the specifics about the new API features and model behavior are documented in our docs, in the [latest model](https://developers.openai.com/api/docs/guides/latest-model) and [prompt guidance](https://developers.openai.com/api/docs/guides/prompt-guidance) guides.

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50The OpenAI Docs skill also includes [specific guidance](https://github.com/openai/codex/blob/6323f0104d17d211029faab149231ba787f7da37/codex-rs/skills/src/assets/samples/openai-docs/references/upgrading-to-gpt-5p4.md) as reference, codifying how to upgrade to the latest model–currently [GPT-5.4](https://developers.openai.com/api/docs/models/gpt-5.4).

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52Codex now automatically comes with the OpenAI Docs skill, so make sure to mention it in your prompt to access all the latest documentation and guidance when building with the OpenAI API.

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54## Build a robust evals pipeline

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56Codex can automatically update your prompts based on the latest prompt guidance, but you should have a way to automate verifying your integration is working as expected.

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58Make sure to build an evals pipeline that you can run every time you make changes to your integration, to verify there is no regression in behavior.

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60This [cookbook guide](https://developers.openai.com/cookbook/examples/evaluation/building_resilient_prompts_using_an_evaluation_flywheel) covers in detail how to do this using our [Evals API](https://developers.openai.com/api/docs/guides/evals).

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62## Related use cases

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64[![](/images/codex/codex-wallpaper-1.webp)

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66### Create browser-based games

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68Use Codex to turn a game brief into first a well-defined plan, and then a real browser-based...

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70Engineering Code](https://developers.openai.com/codex/use-cases/browser-games)[![](/images/codex/codex-wallpaper-1.webp)

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72### Bring your app to ChatGPT

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74Build one narrow ChatGPT app outcome end to end: define the tools, scaffold the MCP server...

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76Integrations Code](https://developers.openai.com/codex/use-cases/chatgpt-apps)[![](/images/codex/codex-wallpaper-3.webp)

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78### Build for iOS and macOS

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80Use Codex to scaffold SwiftUI projects, keep the build loop CLI-first with `xcodebuild` or...

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82Mobile Code](https://developers.openai.com/codex/use-cases/native-ios-macos-apps)