> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.narilabs.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.narilabs.com/_mcp/server.

# Usage and billing

## Usage measurement

| API | Unit                                           | Returned in                                                      |
| --- | ---------------------------------------------- | ---------------------------------------------------------------- |
| TTS | Input characters                               | `x-usage-input-characters` response header                       |
| STT | Input audio duration per utterance, in seconds | `usage.input_audio_seconds` in each `transcript.completed` event |

TTS uses input characters for both Free and Partner models. Characters are counted as Unicode code points after trimming surrounding whitespace and before text normalization. Internal spaces and punctuation count: `"  Hello.  "` counts as **6** characters.

STT reports the audio duration assigned to each utterance, excluding silence discarded by VAD.

These values report usage for the current request or utterance.

## Pricing

Partner models use the rates on [Models and pricing](/models-and-pricing):

* **TTS:** input characters ÷ 1,000,000 × the model’s price per million characters.
* **STT:** input audio seconds ÷ 3,600 × the model’s price per audio hour.

For example, 100,000 input characters cost **$0.50** with TTS Standard. Ten minutes of input audio cost **$0.02** with STT Fast.

## Credits

Successful Partner requests debit credits. Failed and cancelled requests do not. Free-model and Playground requests do not consume credits.

View organization usage and costs on the [Usage page](https://app.trynari.com/usage), and your credit balance on the [Billing page](https://app.trynari.com/billing).