Port to gpt-4o-mini as default

[pamelafox]

Purpose

This PR upgrades to gpt-4o-mini as the default chat completion model.
See my analysis here:
https://blog.pamelafox.org/2025/03/gpt-4o-mini-vs-gpt-35-turbo-for-rag.html
The responses are longer, but it should be overall cheaper,
and it's a more recent model.

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[X] Yes - With existing environments, it will keep gpt-35-turbo
[ ] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by this tutorial
which includes deployment, settings and usage instructions. If text or screenshot need to change in the tutorial,
check the box below and notify the tutorial author. A Microsoft employee can do this for you if you're an external contributor.

[X] Yes - Maybe? It might mention the model
[ ] No

Type of change

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[X] Other... Please describe:

Code quality checklist

See CONTRIBUTING.md for more details.

• The current tests all pass (python -m pytest).
• I added tests that prove my fix is effective or that my feature works
• I ran python -m pytest --cov to verify 100% coverage of added lines
• I ran python -m mypy to check for type errors
• I either used the pre-commit hooks or ran ruff and black manually on my code.

[mattgotteiner]

In a future PR - we may want to add an additional set of prompts for each version of the model

[pamelafox]

I have done a test azd up with my old environment and a brand new environment, all seems well. Merging.

[Jbrocket]

Default azureaideploymentregion is canadaeast (

azure-search-openai-demo/infra/main.bicep

Line 80 in c5bfb22

'canadaeast'

), which doesn't support gpt-4o-mini. https://learn.microsoft.com/en-us/azure/ai-services/openai/concepts/models?tabs=global-standard%2Cstandard-chat-completions#assistants-preview

It doesn't make sense to default to a region that won't work.

[pamelafox]

@Jbrocket Ah! Great catch, I'll send a fix for that now.