### Answer
The sudden increase in pricing for using OpenAI models in your Vapi assistants could be due to several factors, including changes in the underlying costs of the model providers or adjustments in Vapi's pricing structure. It's essential to ensure that your token usage per prompt is optimized, as longer prompts can significantly increase costs due to higher computational requirements.
Additionally, Vapi uses provider keys you set for communication with vendors like OpenAI, and changes in the API or pricing by OpenAI could also reflect in your Vapi usage costs [(1)](
) . If you're seeing discrepancies or unexpected increases, it's important to review the detailed cost breakdown available in your Vapi dashboard to understand which part of your voice pipeline (STT, LLM, TTS) is contributing most to the cost. From there, you can make more informed decisions about potential optimizations or need for changes in your assistant configurations.
For a definitive explanation and to address this specific issue, it would be beneficial to directly consult the detailed billing and usage reports on your Vapi dashboard and compare them with the pricing models provided by OpenAI and other vendors. If this does not clarify the reasons for the price changes, contacting Vapi support directly might be necessary to get specific insights into the pricing adjustments or any potential billing errors.