APIs live at the application layer. Understanding the stack explains why protocol choice matters — each layer has constraints the layer above must work within.
↑ builds on
↑ builds on
↑ builds on
↑ builds on
HTTP versions
Version
Transport
Multiplexing
Push
Used by
HTTP/1.1
TCP (1 req/conn)
No (HoL blocking)
No
Most REST APIs
HTTP/2
TCP (multiplexed)
Yes
Server push
gRPC, modern browsers
HTTP/3
QUIC (UDP-based)
Yes
Yes
CDNs, future APIs
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