226

HTTP 226 IM Used

2xx Success

2xx Success RFC 3229, Section 10.4.1

What is HTTP 226 IM Used?

The 226 (IM Used) status code indicates that the server has fulfilled a GET request for the resource and the response is a representation of the result of one or more instance-manipulations applied to the current instance. This is used with delta encoding to deliver only changes since the last request.

Common Use Cases

  • Delta encoding for bandwidth-efficient updates
  • Incremental content synchronization

Usage Example

When a client requests a resource with an A-IM header specifying delta encoding, the server responds with 226 IM Used and delivers only the changes (delta) since the version specified in the If-None-Match header. The client applies the delta to its local copy.

# Client request using delta encoding
curl -H "A-IM: vcdiff" -H "If-None-Match: \"abc123\"" \
  https://api.example.com/large-dataset

# Server response: 226 IM Used with delta patch

Related Status Codes

Last updated: 21 Jun 2026