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tests/test_litellm/llms/openai/realtime/README.md

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+# OpenAI Realtime Handler Tests
+
+## Important Context: `extra_headers` vs `additional_headers`
+
+### Background
+
+There was confusion about the correct parameter name for passing headers to `websockets.connect()`. This README documents the issue for future maintainers.
+
+### Timeline of Changes
+
+1. **Dec 5, 2025** - Changed `extra_headers` → `additional_headers` (commit `8db7f1b8e4`)
+2. **Dec 18, 2025** - Changed `extra_headers` → `additional_headers` again (PR #17950, commit `9f88d61d10`)
+3. **Jan 15, 2026** - Upgraded `websockets` from 13.1.0 → 15.0.1 (commit `a3cf178e24`, Issue #19089)
+4. **Feb 3, 2026** - Changed `additional_headers` → `extra_headers` (commit `67fc9457e5`)
+5. **Feb 4, 2026** - Updated tests to match current code (this PR)
+
+### The Issue
+
+**The `websockets` library changed its API between versions:**
+
+- **websockets 13.1.0**: Supported `additional_headers` parameter ✅
+- **websockets 15.0.1**: Only supports `extra_headers` parameter ✅
+
+When websockets was upgraded on Jan 15, 2026, the code still used `additional_headers`, which **completely broke the realtime API** for users:
+
+```python
+# This raised: TypeError: got an unexpected keyword argument 'additional_headers'
+await websockets.connect(url, additional_headers={...})
+```
+
+### The Fix
+
+The Feb 3 commit correctly changed the code to use `extra_headers`, which is the **only parameter accepted** by websockets 15.0.1:
+
+```python
+# Correct for websockets 15.0.1+
+await websockets.connect(url, extra_headers={...})
+```
+
+However, the tests weren't updated at that time, causing CI failures.
+
+### Current State (Feb 2026)
+
+✅ **Code uses `extra_headers`** - Correct for websockets 15.0.1+  
+✅ **Tests check for `extra_headers`** - Updated to match the working code  
+✅ **No risk to users** - This is a bug fix, not a regression
+
+### For Future Maintainers
+
+**If you see tests failing related to `additional_headers` vs `extra_headers`:**
+
+1. Check the websockets version in `requirements.txt`
+2. Verify which parameter the websockets library accepts:
+   ```python
+   import inspect
+   import websockets
+   print(inspect.signature(websockets.connect))
+   ```
+3. Ensure both code AND tests use the correct parameter name
+
+**Do NOT change back to `additional_headers`** unless:
+- We downgrade to websockets <14.0, OR
+- The websockets library re-introduces this parameter (unlikely)
+
+### Reference
+
+- websockets documentation: https://websockets.readthedocs.io/
+- websockets changelog: https://websockets.readthedocs.io/en/stable/project/changelog.html
+- Issue #19089: Websocket version error (fixed by upgrading to 15.0.1)