Node.js 27 alpha ships with dozens of breaking changes
The first release under the new annual schedule upgrades V8 and OpenSSL, changes default memory limits, and switches serialisation formats. Native addons need a rebuild.
Node.js 27.0.0-alpha.0.0.0 shipped on 29 October, the first release under the project’s new one-major-per-year schedule. It stays alpha until April 2027, when it becomes Current, with LTS following that October.
The alpha carries a long list of breaking changes. V8 jumps to 15.6.75.13, up from 14.6 in Node 26, enabling Math.sumPrecise(), Iterator.prototype.join() and Iterator.zip() by default. OpenSSL moves to 4.1.0 and now requires OpenSSL 3 or later at build time, dropping the bundled FIPS provider and engine support. When --max-old-space-size isn’t set, the default heap limit becomes half of physical memory, clamped between 256MB and 4GB, and Buffer/ArrayBuffer memory now counts against that limit. v8.serialize(), structuredClone() and postMessage() switch to a format older Node releases can’t read. NODE_MODULE_VERSION moves to 153, so native addons need rebuilding.
node --max-old-space-size=2048 ./server.js
# pin the heap explicitly rather than relying on the new "half of RAM" defaultWhy it matters: none of this belongs in production yet, it’s an alpha. But the breaking-change list is long enough that it’s worth reading now rather than in April, especially the memory default and the serialisation format change, both of which can bite silently if you’re not watching for them.