The server agrees to switch protocols as requested by the client via the Upgrade header.
Quick facts
When does it occur
The server agrees to switch protocols as requested by the client via the Upgrade header.
It belongs to the 1xx Informational class of responses, defined in RFC7231#6.2.2.
Browse all codes in this class: 1xx Informational
Frequently asked questions
101 belongs to the 1xx Informational class and is usually cacheable per headers such as Cache-Control (e.g. 200, 301, 304).
1xx Informational: The server agrees to switch protocols as requested by the client via the Upgrade header.
Sources & standards
Updated 2026-09-13
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