Billing is calculated per Operator execution.

Input characters include the conversation transcript, user prompt, and system prompt passed to the Operator. 

• The conversation transcript is the contents of the conversation itself, prefixed with the participant type (e.g. customer) for each communication. 
• The user prompt is inclusive of the natural language instructions you write, plus training examples and the JSON output schema if using these settings. 
• The system prompt is additional metadata provided by Twilio for the Operator to execute successfully.

If Conversation Memory and/or Enterprise Knowledge is enabled for an Operator to use as context, input characters also include the character count of these tool definitions and retrieved results (if the Operator requests memory or knowledge during execution). 

Output characters include the final response generated by the Operator during that execution. The response is either in plaintext or JSON, depending on the Operator’s configuration. If Conversation Memory and/or Enterprise knowledge is enabled for an Operator to use as context, output characters also include the generated command to make a request for memory or knowledge (if the Operator requests memory or knowledge during execution).