# Adds support for last aggregation formula on meters

## What’s new

We’ve added a `last` aggregation formula to [Billing Meters](https://docs.stripe.com/api/billing/meter.md?api-version=2025-03-31.basil). This formula uses the value from the last event in a time range as the total aggregate value for that period.

## Impact

The new `last` formula lets you bill based on the final meter event received in a billing period for a customer. This complements the existing `sum` and `count` formulas, giving you more billing flexibility.

Your existing Billing Meters continue to use their currently configured aggregation formulas. To use this new feature, create a new Billing Meter with the `last` aggregation formula.

## Changes

#### REST API

| Value  | Change | Enums                                                                                           |
| ------ | ------ | ----------------------------------------------------------------------------------------------- |
| `last` | Added  | `Billing.Meter#create.default_aggregation.formula`, `Billing.Meter.default_aggregation.formula` |

#### Ruby

This change does not affect the Ruby SDK.

#### Python

| Value  | Change | Enums                                                                                             |
| ------ | ------ | ------------------------------------------------------------------------------------------------- |
| `last` | Added  | `BillingMeter.DefaultAggregation.formula`, `billing.Meter.CreateParamsDefaultAggregation.formula` |

#### PHP

| Value  | Change | Enum                                        |
| ------ | ------ | ------------------------------------------- |
| `last` | Added  | `Billing.Meter.default_aggregation.formula` |

#### Java

| Value  | Change | Enum                                                    |
| ------ | ------ | ------------------------------------------------------- |
| `last` | Added  | `billing.MeterCreateParams.default_aggregation.formula` |

#### Node.js

| Value  | Change | Enums                                                                                                |
| ------ | ------ | ---------------------------------------------------------------------------------------------------- |
| `last` | Added  | `Billing.Meter.default_aggregation.formula`, `Billing.MeterCreateParams.default_aggregation.formula` |

#### Go

| Value  | Change | Enum                                     |
| ------ | ------ | ---------------------------------------- |
| `last` | Added  | `BillingMeterDefaultAggregation.Formula` |

#### .NET

This change does not affect the .NET SDK.

## Upgrade

#### REST API

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. If you use an SDK, upgrade to the corresponding SDK version for this API version.
   - If you don’t use an SDK, update your [API requests](https://docs.stripe.com/api/versioning.md) to include `Stripe-Version: 2025-03-31.basil`
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### Ruby

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your Ruby SDK to [v15.0.0](https://github.com/stripe/stripe-ruby/releases/tag/v15.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### Python

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your Python SDK to [v12.0.0](https://github.com/stripe/stripe-python/releases/tag/v12.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### PHP

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your PHP SDK to [v17.0.0](https://github.com/stripe/stripe-php/releases/tag/v17.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### Java

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your Java SDK to [v29.0.0](https://github.com/stripe/stripe-java/releases/tag/v29.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### Node.js

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your Node SDK to [v18.0.0](https://github.com/stripe/stripe-node/releases/tag/v18.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### Go

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your Go SDK to [v82.0.0](https://github.com/stripe/stripe-go/releases/tag/v82.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

#### .NET

1. [View your current API version](https://docs.stripe.com/upgrades.md#view-your-api-version-and-the-latest-available-upgrade-in-workbench) in Workbench.
1. Upgrade your .NET SDK to [v48.0.0](https://github.com/stripe/stripe-dotnet/releases/tag/v48.0.0)
1. Upgrade the API version used for [webhook endpoints](https://docs.stripe.com/webhooks/versioning.md).
1. [Test your integration](https://docs.stripe.com/testing.md) against the new version.
1. If you use Connect, [test your Connect integration](https://docs.stripe.com/connect/testing.md).
1. In Workbench, [perform the upgrade](https://docs.stripe.com/upgrades.md#perform-the-upgrade). You can [roll back the version](https://docs.stripe.com/upgrades.md#roll-back-your-api-version) for 72 hours.

Learn more about [Stripe API upgrades](https://docs.stripe.com/upgrades.md).

## Related changes

- [Adds subscription item-level billing periods and removes subscription-level periods](https://docs.stripe.com/changelog/basil/2025-03-31/deprecate-subscription-current-period-start-and-end.md)
- [Invoicing resources now specify how they were generated](https://docs.stripe.com/changelog/basil/2025-03-31/adds-new-parent-field-to-invoicing-objects.md)
- [Adds new webhook event types for Billing Meters](https://docs.stripe.com/changelog/basil/2025-03-31/billing-meter-webhooks.md)
- [Adds new webhook event types for billing credits](https://docs.stripe.com/changelog/basil/2025-03-31/billing-credit-webhooks.md)