The Ultimate Guide to HTTP Status Codes (100–599)
A complete reference guide to all HTTP status codes from 100 to 599, with explanations and common use cases.
Feb 28, 2026
226
HTTP 226 IM Used
2xx Success
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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 patchRelated Status Codes
Last updated: 17 Aug 2026
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