docs: update litellm models configuration description

Author: adzmitry

docs/admin/configuration/extensions/litellm-proxy/model-configuration.md

@@ -144,6 +144,60 @@ Each model entry in the `model_list` array consists of three main sections:
 
   </details>
 
+- **`api_base`**: Backend provider API base URL. Required for Azure OpenAI.
+
+  <details>
+  <summary><strong>Example: API Base URL</strong></summary>
+
+  ```yaml
+  model_list:
+    - model_name: claude-sonnet-4-5-20250929
+      litellm_params:
+        model: bedrock/us.anthropic.claude-sonnet-4-5-20250929-v1:0
+      # ... additional configuration fields
+
+    - model_name: gpt-5-2025-08-07
+      litellm_params:
+        model: azure/gpt-5-2025-08-07
+        // highlight-next-line
+        api_base: https://custom-domain-name.openai.azure.com/
+      # ... additional configuration fields
+
+    - model_name: gemini-3.1-pro
+      litellm_params:
+        model: vertex_ai/gemini-3.1-pro-preview
+      # ... additional configuration fields
+  ```
+
+  </details>
+
+- **`api_version`**: Backend provider API version. Applicable for Azure OpenAI.
+
+  <details>
+  <summary><strong>Example: API Version</strong></summary>
+
+  ```yaml
+  model_list:
+    - model_name: claude-sonnet-4-5-20250929
+      litellm_params:
+        model: bedrock/us.anthropic.claude-sonnet-4-5-20250929-v1:0
+      # ... additional configuration fields
+
+    - model_name: gpt-5-2025-08-07
+      litellm_params:
+        model: azure/gpt-5-2025-08-07
+        // highlight-next-line
+        api_version: "2025-04-01-preview"
+      # ... additional configuration fields
+
+    - model_name: gemini-3.1-pro
+      litellm_params:
+        model: vertex_ai/gemini-3.1-pro-preview
+      # ... additional configuration fields
+  ```
+
+  </details>
+
 - **`litellm_credential_name`**: Reference to authentication credentials configured in secrets
 
   <details>
@@ -586,6 +640,26 @@ model_list:
 
 ### GPT-5 series
 
+Generic configuration for GPT-5 Series models is the following.
+
+```yaml
+- model_name: gpt-5-2025-08-07
+  litellm_params:
+    model: azure/gpt5_series/deployment-name
+    api_base: https://api-base.openai.azure.com/
+    litellm_credential_name: azure_openai_credential
+  model_info:
+    id: gpt-5-2025-08-07
+    base_model: azure/gpt-5-2025-08-07
+    label: "GPT-5 2025-08-07"
+```
+
+The very new models may require a particular version of Azure API. For example, gpt-5.3-codex models require API version `2025-03-01-preview` or newer.
+Therefore, if your CLI client doesn't add compatible `api-version` to the request or CodeMie instance is configured to use older API version, the model may not work.
+To fix the issue, set `api_version` parameter to the `litellm_params` as shown [below](#gpt-53-codex-with-chat-compatibility-mode).
+
+Otherwise, if client explicitly set `api-version` in request LiteLLM uses it instead of configured value.
+
 #### GPT-5
 
 <details>
@@ -788,6 +862,28 @@ model_list:
 
 </details>
 
+#### GPT-5.3 Codex with Chat Compatibility Mode
+
+<details>
+<summary><strong>GPT-5.3 Codex</strong></summary>
+
+```yaml
+# US Region
+- model_name: gpt-5.3-codex-2026-02-24
+  litellm_params:
+    model: azure/responses/gpt-5.3-codex-2026-02-24
+    api_base: https://api-base-eastus2-0.openai.azure.com/
+    litellm_credential_name: default_azure_openai_credential
+    // highlight-next-line
+    api_version: "2025-04-01-preview"
+  model_info:
+    id: gpt-5-3-codex-2026-02-24-eastus2-0
+    base_model: azure/gpt-5.3-codex
+    label: "GPT-5.3 Codex 2026-02-24"
+```
+
+</details>
+
 ### GPT-5.4 series
 
 #### GPT-5.4