Node.js 27.0.0-alpha.0.0.0 Released with V8 15.6 Update and Core Changes

V8 Engine Update and New Language Features

Node.js 27.0.0-alpha.0.0.0 incorporates an upgrade to the V8 engine, moving from version 14.6 to 15.6.75.13. This update enables several new JavaScript language features by default, including Math.sumPrecise(), Intl.Locale.prototype.variants, Iterator.prototype.join(), Iterator.prototype.includes(), Iterator.zip(), and Iterator.zipKeyed().

Additionally, experimental features such as import defer, ImmutableArrayBuffer, and RegExp buffer boundaries are available behind specific flags for early testing.

Memory Management and Serialization Changes

The default heap size limit has been revised; when --max-old-space-size is not explicitly set, it now defaults to half of the physical memory, constrained between 256 MB and 4 GB. Memory consumed by Buffer and ArrayBuffer instances now contributes to this heap limit, which may require applications relying on previous defaults to explicitly set --max-old-space-size.

Serialization methods like v8.serialize(), structuredClone(), and postMessage() now use a new format that is incompatible with older Node.js releases. The v8.cachedDataVersionTag() and compile cache will also change with every V8 patch in Node.js, not just major V8 version updates.

Observable Behavior and Tooling Updates

Several observable behavior changes are present in this alpha release. Math methods now use LLVM's libm, potentially leading to minor differences in precision. Math.random() sequences will change for a given --random-seed. The error.stack property is no longer looked up via the prototype chain, and await incurs fewer microtasks. Array.prototype.sort() now utilizes PowerSort for large arrays while maintaining stability.

Heap snapshots now include internal objects, numeric values, and full script sources, resulting in approximately double the snapshot generation time and file size. For WebAssembly, asm.js is no longer compiled to WebAssembly, and experimental flags like --experimental-wasm-<name> have been renamed to --wasm-<name>.

Build and Crypto Module Adjustments

The build process for Node.js 27.0.0-alpha.0.0.0 no longer includes the bundled FIPS provider and now requires OpenSSL 3 or later. Support for Intel macOS has been downgraded to experimental. In the crypto module, DEP0093 has reached End-of-Life, legacy OpenSSL code paths have been removed, and digest and update input/output encodings are now validated.