> ## Documentation Index
> Fetch the complete documentation index at: https://openrouter.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Period

Time grain of each row. `day` (default) returns the per-UTC-day series; `week` buckets by ISO week start; `month` buckets by month start. With `category` or `language_type` only `week` (default) and `month` are available — `day` is rejected with a 400 because those datasets are aggregated weekly. For those sampled datasets `period=month` buckets each week by its week-start month, so totals are approximate at month boundaries.

## Example Usage

```go theme={null}
import (
	"github.com/OpenRouterTeam/go-sdk/models/operations"
)

value := operations.PeriodDay

// Open enum: custom values can be created with a direct type cast
custom := operations.Period("custom_value")
```

## Values

| Name          | Value |
| ------------- | ----- |
| `PeriodDay`   | day   |
| `PeriodWeek`  | week  |
| `PeriodMonth` | month |