ENGINE code removed from the OpenSSL Library

OpenSSL 4.0, to be released in April 2026, is the first major
release since 3.0 which replaced
the ENGINE interface with
Providers. Removing ENGINEs is a
primary goal of this major release and this post describes the change
agreed to by both the OpenSSL Corporation and OpenSSL Foundation.

Summary

All symbols defined in openssl/engine.h have been removed from the
shared library in
OpenSSL 4.0. Applications that use the ENGINE API will fail to compile
using the default build settings. This behavior matches what happens
in previous versions when building OpenSSL with the no-engine
configuration
option
with current versions. Up-to-date applications should not include
openssl/engine.h at all.