Add link to GH billing and premium requests docs

Author: ntrogh

docs/copilot/chat/chat-sessions.md

@@ -136,7 +136,7 @@ The following examples illustrate how to invoke a subagent:
 Agents enable you to perform AI coding tasks asynchronously in the background. This allows you to continue working in VS Code while the agent processes your requests. These agents are different from chat sessions in VS Code, since agents work in the background, while chat sessions are interactive and require your real-time input. Agents can also run in different environments, such as locally on your machine or remotely in the cloud.
 
 > [!TIP]
-> The OpenAI Codex agent enables you to use your Copilot Pro+ subscription to authenticate and access Codex without additional setup.
+> The OpenAI Codex agent enables you to use your Copilot Pro+ subscription to authenticate and access Codex without additional setup. Get more information about [GitHub Copilot billing and premium requests](https://docs.github.com/en/copilot/concepts/billing/copilot-requests) in the GitHub documentation.
 
 ### Agent Sessions view
 

release-notes/v1_105.md

@@ -149,13 +149,13 @@ The new [Agent Sessions view](https://code.visualstudio.com/docs/copilot/chat/ch
 
 > **Note**: This feature is currently only available in [VS Code Insiders](https://code.visualstudio.com/insiders/).
 
-The new [Agent Sessions view](https://code.visualstudio.com/docs/copilot/chat/chat-sessions#_agent-sessions-view) in VS Code Insiders now integrates with OpenAI Codex. Manage both local and cloud-based agent sessions from a unified interface, making it easier to track progress and delegate tasks across multiple AI coding assistants.
+The new [Agent Sessions view](https://code.visualstudio.com/docs/copilot/chat/chat-sessions#_agent-sessions-view) in VS Code Insiders now also integrates with OpenAI Codex. Manage both local and cloud-based agent sessions from a unified interface, making it easier to track progress and delegate tasks across multiple AI coding assistants.
 
 ![Screenshot of the Agent Sessions view showing an OpenAI Codex session.](images/1_105/agent-sessions-codex.png)
 
 In addition, OpenAI Codex can now be powered by your Copilot subscription. Once the Codex extension is installed and configured, Codex will automatically appear in the Agent Sessions view. Use your Copilot Pro+ subscription to authenticate and access Codex without additional setup.
 
-Download [VS Code Insiders](https://code.visualstudio.com/insiders/) to try out this functionality. Read more about this in the announcement [GitHub blog post](https://aka.ms/github-changelog-codex-agent).
+Get more information about [GitHub Copilot billing and premium requests](https://docs.github.com/en/copilot/concepts/billing/copilot-requests) in the GitHub documentation.
 
 ## Chat