OpenSSL 4.1.0 was released on 23 October 2026 as the first feature release of the 4.x series after OpenSSL 4.0. It adds DTLS 1.3, GREASE and faster ML-DSA, ML-KEM and AES-CBC code paths, but it also removes some build options and ships with four known DTLS issues. For system administrators, the practical question is which branch to run in production now that several OpenSSL versions are about to reach end of life.

OpenSSL 4.1 for sysadmins in 30 seconds

OpenSSL 4.1.0 shipped on 23 October 2026 and keeps API and ABI compatibility with 4.0.
It adds DTLS 1.3, GREASE, DTLS in the SSL listener API and the IKEv2 KDF.
ML-DSA, ML-KEM and AES-CBC decryption get faster on x86_64 and ppc64le, with no official benchmark figures.
no-ecdsa, no-ecdh and the Windows CE and Itanium targets are gone; tsget now needs Net::Curl::Easy.
OpenSSL 3.6 support ends on 1 November 2026, while 3.5 LTS runs until April 2030.

This is not a long-term support (LTS) release. Under the project’s policy, non-LTS releases after 3.5 get 13 months of full support, while the current LTS branch, 3.5, is maintained until 8 April 2030. On servers, most teams will keep relying on their distribution’s package, which decides when and how each branch arrives.

What changes in protocols and performance

The headline addition is DTLS 1.3 (RFC 9147), the UDP flavour of TLS 1.3. It mainly matters for VPNs, real-time applications and devices that use DTLS, and the project points to the ossl-guide-dtlsv13(7) manual page for configuration details. The SSL listener API, designed to accept connections centrally, now supports DTLS as well.

GREASE (RFC 8701) also lands. It inserts reserved, meaningless values into the TLS handshake to expose servers, load balancers or firewalls that break when they see unknown extensions. For operators, that means a badly implemented middlebox may show itself sooner. The list is completed by the IKEv2 key derivation function, useful for IPsec implementations, and initial support for the Elbrus 2000 (e2k) architecture.

On the performance side, the release optimises ML-DSA and ML-KEM NTT operations on ppc64le, ML-DSA on x86_64, AVX-512 SHAKE x4 for ML-DSA, and AES-CBC decryption with AVX-512 and VAES. The release notes do not include speed-up figures, so it is worth running openssl speed on your own hardware before drawing conclusions. Post-quantum algorithms first arrived in the library with the 3.5 branch, as covered in OpenSSL 3.5 LTS Brings Server-Side QUIC, Post-Quantum Crypto, and Performance Enhancements.

What to check before building or upgrading

Anyone building OpenSSL from source should review their scripts. The no-ecdsa and no-ecdh Configure options are gone because, according to the project, they never really disabled those implementations; the alternative is no-ec, which removes elliptic curve support altogether. The VC-WIN64I (Windows on Itanium) and VC-CE (Windows CE) targets are also dropped, while new VC-WIN32-MSVC2013 and VC-WIN64A-MSVC2013 targets fill C99 gaps in that compiler.

Another easy-to-miss detail is tsget, the timestamp request utility. It now uses the Net::Curl::Easy Perl module instead of the abandoned WWW::Curl::Easy, so systems that depend on it need the new module installed before upgrading. To check which version and build options a system has, run:

openssl version -a

The project also lists four known issues, all in DTLS. After a DTLS 1.3 KeyUpdate is received, other pending post-handshake records, such as a NewSessionTicket, are dropped from the retransmission buffer. The DTLS listener can report a permanent failure as SSL_ERROR_WANT_READ and a retryable write failure as SSL_ERROR_SYSCALL. And a DTLS 1.3 server may abort the handshake after packet loss. Anyone planning to run DTLS 1.3 in production should wait for fixes or test thoroughly.

A support calendar with near deadlines

OpenSSL’s release strategy page sets these dates: 3.4 lost support on 22 October 2026, 3.6 loses it on 1 November 2026, 4.0 is supported until 14 May 2027 and 3.5 LTS until 8 April 2030. Versions 3.0, 1.1.1 and 1.0.2 now only receive fixes through paid extended support. The next major release, OpenSSL 5.0, is planned for October 2027, six months after the next LTS. Spanish-language security site OpenSecurity has also published a rundown of this release: OpenSSL 4.1 añade DTLS 1.3 y GREASE y acelera la criptografía poscuántica.