What's New in 1.15

Summary

Google open-sourced mod_pagespeed in 2010. The last open-source release shipped in 2020, under the Apache incubator, and the project was archived in 2025. We-Amp picked up where the original team left off and built mod_pagespeed 1.15 — a commercially supported, drop-in compatible continuation.

Everything below ships in 1.15 and is included in the subscription. If you are here to improve Core Web Vitals, 1.15 brings the same server-layer optimizations — byte-weight, render-blocking, image, and caching, the levers behind LCP — to Apache, nginx, and IIS.

Security patches

All known CVEs from the open-source project have been patched. We maintain an ongoing security review process and ship patches as part of regular updates — see the release notes for the per-release security entries.

Cyclone Cache

The original mod_pagespeed used its own file-based cache that could grow unpredictably and suffered from lock contention under high concurrency. mod_pagespeed 1.15 replaces it with Cyclone Cache — a new cache backend shared with ModPageSpeed 2.0.

Key improvements:

• Fixed-size cache file — no more runaway disk usage
• Scan-resistant, no cache-cleaning passes — Cyclone stays within its size bound inline, so there is no periodic background scan to trim the cache the way the original file cache needed; its eviction also resists pollution from one-off request floods, so your hot content stays cached
• Lock-free reads — concurrent requests don’t block each other
• Memory-mapped I/O — the OS manages caching in RAM automatically
• Shared across processes — works correctly with nginx worker processes
• Warm restarts, nothing to configure — the open-source line kept the shared-memory metadata cache warm across restarts with periodic checkpoints to disk, which left a snapshot-interval loss window and one more knob to tune; in v1.15.0+r17 and later, metadata and page properties write through to Cyclone continuously, so a restart comes back warm with no checkpoint to schedule; in v1.15.0+r18 and later this data is held in a dedicated area of the cache, so heavy image traffic can’t push it out
• Served by reference, not copied (v1.15.0+r18 and later) — cached optimized assets are carried into the server’s output by reference to the memory-mapped cache instead of being copied per request (CycloneZeroCopyServe; on by default on nginx, experimental opt-in on Apache and IIS), and an experimental fully zero-copy serve mode (CycloneZeroCopy) is available

Your existing pagespeed directives continue to work. Cyclone Cache is the new default backend — no configuration change required.

Multi-platform support

The open-source mod_pagespeed supported nginx and Apache. mod_pagespeed 1.15 adds IIS as a first-class platform — replacing IISpeed — plus an ASP.NET Core sidecar package (WeAmp.PageSpeed, preview):

Platform	Status
nginx	Stable — prebuilt, signed apt/yum package for Debian 11/12/13 and Ubuntu 22.04/24.04 (amd64 + arm64) plus AlmaLinux/RHEL/Rocky 9 (x86_64 + aarch64) and 10 (x86_64), each pinned to that distro’s stock nginx; contact us for a pinned build on other nginx versions
Apache	Stable — drop-in replacement for the Google/Apache module
IIS	Stable — native module for Windows Server 2019 and later (IIS 10+) — replaces IISpeed

All platforms are built from a single codebase and share the same filter implementations.

Modern build system

mod_pagespeed 1.15 is built with Bazel, replacing the original GYP/Make build system. This means:

• Reproducible builds — every build produces identical output
• Pre-built packages — .deb and .rpm from signed apt/yum repositories, and a signed .msi for IIS — no compiling from source
• Hermetic toolchain — no dependency on system libraries

What stays the same

mod_pagespeed 1.15 is a drop-in replacement. These things haven’t changed:

• All existing pagespeed configuration directives work as before
• All filters are present and behave identically
• The X-Mod-Pagespeed (Apache) / X-Page-Speed (nginx) response header is still emitted
• Admin and statistics pages work the same way
• .htaccess support on Apache is preserved

If your site works with the open-source version, it works with 1.15. Swap the binary, keep your config.