Ladybird newsletter spotlights Rust gains, 4K YouTube and faster JavaScript execution

Ladybird just hit the kind of milestone that changes how a browser feels in daily use: YouTube quality selection now reaches 4K on most videos, JavaScript got faster, and the new Rust regex engine is roughly 6x quicker on Octane. That is not brochureware. It is the sort of progress that makes a browser stop feeling like an experiment and start looking like a real alternative.

The YouTube work comes from partial Media Source Extensions support for VP9 video and Opus audio in WebM. Ladybird says the feature is still behind the expose-experimental-interfaces flag, and it is not pretending the job is finished. Playback performance still needs work, and memory use is expected to stay high for now because buffered data is not yet evicted when the page asks for it. Even so, getting quality selection working up to 4K on most videos is a concrete daily-use win, not a lab demo.

The JavaScript side showed the same kind of practical engineering. Ladybird introduced AsmInt, a hand-written assembly bytecode interpreter for LibJS built around a custom DSL that compiles to native x86_64 and AArch64 assembly. The hot paths, arithmetic, comparisons, and property access, stay in hand-written assembly, while C++ handles the more complex cases. In the same month, Ladybird said benchmark scores improved materially, with Kraken at 1.44x, Octane at 1.37x, and SunSpider at 1.69x.

Regex got the biggest raw speed headline. Ladybird rewrote its ECMA-262 regex engine in Rust, switching to an AST-first design so it can analyze and transform patterns before generating bytecode. The payoff is a dramatic one: the Octane regexp benchmark now runs about 6x faster. Ladybird also imported the V8 and WebKit regex test suites to keep correctness from slipping while the engine gets faster.

The browser’s JavaScript parser now runs on worker threads as part of the broader performance push. That sits on top of a deeper Rust transition that Ladybird announced on February 23, 2026, after previously testing Rust in 2024 and deciding it was not a fit for its older C++-style OOP model. By February, the project had removed all Swift code and landed a complete Rust reimplementation of the LibJS frontend pipeline, covering the lexer, parser, AST, scope collector, and bytecode generator. Ladybird says that port took about two weeks, produced around 25,000 lines of Rust, passed 52,898 test262 tests plus 12,461 Ladybird-specific tests with zero regressions, and generated byte-for-byte identical bytecode to the C++ version.

That is the real story here. Ladybird is still chasing an alpha release on Linux and macOS in 2026, but with 352 merged PRs, 49 contributors, 19 first-time contributors, and new $1,000 sponsorships from Zain Allarakhia and zacoons, it is starting to look less like a curiosity and more like a browser project with momentum.