## Summary
This change improves how model names are handled inside `_base_client.py`.
Previously, if a developer passed a model name with uppercase letters 
(e.g. `"GPT-4O-MINI"`) or extra spaces (e.g. `" gpt-4o-mini "`), 
the client would send it directly to the API. Since the backend is strict and only accepts exact lowercase identifiers (like `"gpt-4o-mini"`), this would cause:
```
BadRequestError: unexpected model name format
```
---
## Changes
- Added a normalization step in `BaseClient._build_request`:
 - Automatically converts model names to lowercase. 
 - Removes leading/trailing whitespace. 
---
## Why
This small improvement:
- Prevents confusing **400 errors** when users accidentally use uppercase or spacing. 
- Makes the SDK more developer-friendly and forgiving without altering API behavior. 
- Increases compatibility across both **OpenAI** and **Gemini** endpoints (since Gemini APIs accessed through the OpenAI Agent SDK also require strict lowercase model identifiers). 
- Keeps compatibility with existing OpenAI models — now `"GPT-4"`, `" gPt-4 "`, and `"gpt-4"` all resolve correctly. 
---
## Examples
### Before (OpenAI model)
```python
client.chat.completions.create(model="GPT-4O-MINI", messages=[...])
# ❌ Error: unexpected model name format
```
### After (OpenAI model)
```python
client.chat.completions.create(model="GPT-4O-MINI", messages=[...])
# ✅ Works: normalized to "gpt-4o-mini"
```
---
### Before (Gemini model used with `OpenAIChatCompletionsModel`)
```python
client = AsyncOpenAI(
 api_key=API_KEY,
 base_url="https://generativelanguage.googleapis.com/v1beta/openai/"
)
model = OpenAIChatCompletionsModel(
 model=" Gemini-2.5-flash ", # note extra spaces / mixed casing
 openai_client=client,
)
# ❌ Error: unexpected model name format
```
### After (Gemini model with fix applied)
```python
model = OpenAIChatCompletionsModel(
 model=" GeMiNi-2.5-flAsH ",
 openai_client=client,
)
# ✅ Works: normalized to "gemini-2.5-flash"
```
---
## Impact
- 🚫 No breaking changes. 
- ✅ Safer and more user-friendly client behavior. 
- ✅ Prevents tricky case/spacing bugs for both OpenAI and Gemini model IDs. 
- ✅ Helps beginners and production apps avoid unnecessary API errors. 
---
## 🔑 Why This Matters
Whether using standard **OpenAI models** (`gpt-4o`, `gpt-4o-mini`, etc.) or integrating **Google Gemini models** via the OpenAI Agent SDK, developers will no longer run into frustrating case/format errors just because of casing or whitespace.
This makes the SDK **robust, cross-compatible, and beginner-friendly**.