Yes, when you use the large language models, you pay OpenAI, Google or Anthropic for it. Here are their plans and pricing:

• OpenAI - https://openai.com/api/pricing/ 
• Google - https://ai.google.dev/pricing 
• Anthropic - https://console.anthropic.com/settings/plans 

For all my testing during development for over a year now, so far I only payed $15,66 in total, so it is very affordable.

For Google you even get a first time $280 credit!

1. Uninstall the previous version
   1. Open Blender
   2. Go to Edit -> Preferences -> Add-ons
   3. Search for Chat Companion
   4. Click Remove
   5. Restart Blender!
2. Install the new version (follow the steps here in the FAQs)
   1. Go to https://blendermarket.com/account/orders 
   2. Click on "Go to Downloads" for Chat Companion
   3. Download the latest Version

• From recent Blender version 4.1 down to 3.3.5 LTS

• OpenAI GPT-4o (Omni) - their best, latest and cheapest model!
  
• OpenAI GPT-4 Turbo
• OpenAI GPT-4
  
• OpenAI GPT-3.5 Turbo

• Google Gemini 1.5 Pro - this one has an amazingly huge context window of over 1 million token!
  
• Google Gemini 1.0 

• Claude 3 Opus - Their most powerful model!
• Claude 3 Sonnet
• Claude 3 Haiku

Yes! You can get your key here https://platform.openai.com/account/api-keys after you signed up. Once you have your key, just insert it into the addon preferences in Blender and you are good to go.

Step by step:

1. Go to https://platform.openai.com/account/api-keys
2. Click on "create new secret key"
3. 
   
4. Click on "create secret key" in the popup
5. 
   
6. Copy your key
7. 
   
8. Enter it in the addon preferences
9. 
   

To use GPT-4 you need to be accepted after enrolling into the waitlist of OpenAI here: https://openai.com/waitlist/gpt-4-api

As any other Blender Addon. Download the Chat Companion.zip file and leave it as a zip-file, don't unpack it.

1. Open Blender (Restart Blender after uninstalling an older version of Chat Companion)
2. Go to Edit -> Preferences -> Add-ons
3. Click "Install...", navigate to the Chat Companion.zip file and click "Install Add-on"
4. Enable the addon with the checkmark
5. Activate the addon by checking the Checkbox next to it
6. Enter your API Key (get it here: https://platform.openai.com/account/api-keys)

It should then look like this:

You will find the Addon panel in the sidebar of the 3D View (Open/Close with n on your keyboard):