---
title: Minimum c15t version
description: Choose the oldest c15t version your project serves, and refuse
  requests from older clients.
lastModified: "2026-11-03T13:03:32Z"
---
New projects start at 3.x. Older projects serve c15t 2.x and 3.x clients side by side, so you can move a site from 2.x to 3.x without downtime. Once every site on the project runs 3.x, set the minimum to 3.x and the project stops serving 2.x.

This setting is rolling out and may not appear in your organization yet.

## Why set a minimum

The c15t version comes from the request, not your site, so anyone can reach the 2.x runtime while the project serves it. A 3.x minimum:

* keeps an unfixed 2.x runtime out of reach when a security fix ships for 3.x first, or only for 3.x
* leaves less code reachable once your sites no longer need 2.x

It doesn't update your sites, and it doesn't protect against bugs in 3.x.

## What changes at 3.x

* A request that names a 2.x version, in the `x-c15t-version` header or the `v` parameter on `/init`, gets `409 Conflict`. No c15t code runs for it.
* A request that names no version is served as 3.x.
* Requests from 3.x clients are served as before.

Sites that still run c15t 2.x stop loading the banner until they update to 3.x.

## Raise the minimum

1. Update every site on the project to c15t 3.x.
2. In the Dashboard, open the project's Consent section and select **Settings**.
3. Under **Minimum c15t Version**, choose **3.x**.
4. Read the warning. It shows how many hours of the last 7 days the project served c15t 2.x.
5. Select **Save changes**. If that number is not zero, or Inth has no data yet, confirm with **Refuse 2.x**.

The change applies as soon as it saves.

## Go back to 2.x

Choose **2.x** under **Minimum c15t Version** and save. The project serves 2.x and 3.x clients again. Do this on a new project before you connect a site that still runs c15t 2.x.

## Projects on c15t 1.x

Projects whose consent backend still runs c15t 1.x do not show this setting. Select **Upgrade to v2** on the same Settings page first.