# What gets counted

> The kinds of AI cost ai-tally adds up, and how it splits them by feature and by customer.

Each AI call your app makes becomes one span in ai-tally. A span is one traced unit of work: which model was called, how many tokens it used, and what it cost. ai-tally adds spans up to show where your money goes.

## Six kinds of cost

An AI feature costs more than the model call. ai-tally sorts spend into six kinds, called layers:

| Layer | What it is | Where the numbers come from |
|---|---|---|
| **LLM** | Calls to AI models, like a chat completion. | Your calls, through the proxy, the SDK or OpenTelemetry. |
| **Embeddings** | Turning text into vectors for search. | Your calls, through the SDK or OpenTelemetry. |
| **Tool calls** | Paid APIs your feature calls, like a web search API. | Your calls, recorded with the SDK or OpenTelemetry. |
| **Vector DB** | Searches against a vector database. | Your calls, recorded with the SDK or OpenTelemetry. |
| **Compute** | The servers and functions your AI feature runs on. | Your cloud bill, through a connection on the **Connectors** page. |
| **Egress** | Data sent out of your cloud to the internet. | Your cloud bill, through a connection on the **Connectors** page. |

**Cost Explorer** shows all six, over time.

## Cost per feature

A feature is a part of your product that uses AI, like `support-chat` or `summarize`. You name it with a feature tag:

- **Proxy:** the `X-Tally-Feature-Tag` header.
- **Python SDK:** `feature_tag` in `tally.init` or `tally.start_trace`.
- **OpenTelemetry:** the `gen_ai.feature_tag` attribute.

Calls without a tag are counted as `untagged`. To see cost by feature, open **Cost Explorer** and group by feature.

## Cost per customer

A customer here means one of *your* customers, the people or companies using your product. ai-tally shows what each one costs you on the **Cost per Account** page under **Analyze**.

To count a call toward a customer, you attach a hashed customer id that cannot be traced back. It works like this:

- **Each organization has its own secret key.** Your customer id is turned into a 64-character code with that key.
- **The same id always gives the same code** in your organization, so all of a customer's calls add up together.
- **Nobody can turn the code back into the id.** Codes from two different organizations never match.
- **ai-tally never stores your real customer ids.** The Python SDK makes the code inside your app. With the proxy or OpenTelemetry, you make it yourself with `python -m tally.hash_account your-customer-id`.

### Shared costs

Compute and egress come from your cloud bill as one total per day. They cannot be tied to a single customer's calls, so ai-tally shares them out. Cost per Account shows these shared amounts separately from each customer's direct cost, and names the rule it used:

- **Pro rata on direct spend** (the default): each customer's share of compute and egress matches their share of direct AI cost.
- **Even split across accounts:** compute and egress are split equally across every customer and the untagged calls.

## Next

- See how each call is priced, and why some costs show a blank: [Prices and blanks](https://ai-tally.com/docs/cost/prices-and-blanks).