JetStream 3.0 Launches to Fix Browser Benchmark 'Infinity Problem'
Breaking: Apple, Google, and Mozilla Release JetStream 3.0
Today, the WebKit team, alongside colleagues at Google and Mozilla, announced JetStream 3.0, a major overhaul of the cross-browser benchmark suite. The update directly addresses a critical flaw that emerged in JetStream 2.2: when browser engines optimized WebAssembly startup time to below one millisecond, the benchmark's scoring formula produced infinite scores, rendering the test meaningless.
“The zero-millisecond startup time was a sign that benchmarks had become irrelevant for modern WebAssembly workloads,” said a WebKit engineer. “JetStream 3 fixes this by introducing sub-millisecond precision and a new scoring model that reflects real-world performance.”
What Was the Infinity Problem?
JetStream 2 measured WebAssembly performance in two phases: Startup and Runtime. The startup score was calculated as 5000 / time. As engines shaved off milliseconds, startup times for smaller workloads dropped to exactly zero milliseconds due to Date.now() rounding. The score then became infinity.
While developers might celebrate an infinite score, the anomaly made the benchmark useless for comparing browser performance. The JetStream 2.2 patch clamped the score to 5000, but this was a temporary fix. “We knew we had outgrown the old benchmarks,” the engineer added. “Wasm is now critical for image decoders, UI frameworks, and library loading—startup time matters on the critical path.”
Background: The Evolution of WebAssembly Benchmarking
JetStream 2 was released when WebAssembly was in its infancy. Early adopters were large C/C++ projects that tolerated long startup times for high throughput. The benchmark split Wasm into two phases to reflect that trade-off. Over time, engines like JavaScriptCore optimized instantiation so aggressively that startup became virtually instant.
“We optimized the startup path to the point where for certain workloads, time effectively reached zero,” said the WebKit team. “That told us the benchmark no longer reflected the real web—where Wasm is in the critical path for many page loads.”
What This Means for Browser Performance
JetStream 3.0 represents a fundamental shift in performance measurement. It abandons the startup/runtime split and instead uses a unified scoring system with sub-millisecond precision. New workloads simulate modern web applications where Wasm interacts with other libraries and UI frameworks.
For users, this means more realistic speed comparisons across browsers. For developers, it provides actionable insights into real-world bottlenecks. “JetStream 3 is not just a refresh—it’s a rethinking of what matters for the web,” the engineer concluded. “We expect it to drive optimizations that benefit everyone.”
Impact summary: The update ensures that benchmark scores remain finite and meaningful, while pushing browser engines to optimize for scenarios that users actually encounter—like loading a library that uses Wasm for image decoding alongside JavaScript for interactivity.
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