# API Changelog

Public changes to the BillerAPI client API. Entries document additive changes to the [/v1 contract](/docs/concepts/versioning.md) and any active deprecations.

## Active deprecations

### `?env=sandbox|production` query parameter

- **Sunset:** 2026-08-23
- The `?env=` query parameter on the activity and logs endpoints (`/v1/activity`, `/v1/activity/:id`, `/v1/activity/:id/deliveries`, `/v1/activity/:id/related`, `/v1/activity.csv`, `/v1/logs`) is deprecated. Callers still receive a 200 with the parameter silently ignored, and responses carry the RFC 9745 headers `Deprecation: true` and `Sunset: 2026-08-23`. After the sunset date the deprecation headers are removed; the parameter itself stays accepted-and-ignored so long-tail SDK callers never break. Environment is determined by the API key you authenticate with, not by a query parameter.
- **Migrate:** [Environments](/docs/concepts/environments)

## Changes

### Launch — First public client API

- Bearer API keys for sandbox and production server-side requests.
- Hosted account-linking flow with link token creation and public token exchange.
- Bill retrieval APIs for connected biller accounts.
- Signed webhook delivery for link and bill lifecycle events.
- OpenAPI 3.0 document for typed client generation.