# 226 IM Used

> The server has fulfilled a request for the resource and the response represents the result of applying one or more instance manipulations.

Source: https://apiguide.dev/status-codes/226
Class: success
Defined in: RFC 3229 <https://www.rfc-editor.org/rfc/rfc3229.html>
Updated: 2026-07-09

## What does HTTP status code 226 mean?

The 226 IM Used status code indicates that the server has fulfilled a `GET` request and the response is a representation of the result of one or more instance manipulations applied to the current instance, as negotiated using the `A-IM` request header.

## When to use it in APIs

Defined by RFC 3229 for delta encoding, where a client that already holds an older version of a resource asks the server to return only the difference (the "delta") rather than the full body. The server responds with 226 and an `IM` header identifying the instance manipulation (e.g., a diff algorithm) used to produce the payload, letting the client reconstruct the current version while saving bandwidth.

## How it compares to other codes

* **200 OK**: Returns the full current representation, whereas 226 returns only a delta relative to a version the client already has.
* **206 Partial Content**: Returns a byte range of a resource requested via the `Range` header, while 226 returns a computed difference negotiated via the `A-IM` header.