December 2, 2025
Benchmarks and brawls
Comparing AWS Lambda ARM64 vs. x86_64 Performance Across Runtimes in Late 2025
ARM grabs the speed crown, Rust flexes, and commenters roast the test
TLDR: New open-source tests crown Rust on ARM64 as the fastest and most efficient for AWS Lambda, with Python 3.11 on ARM also strong. Comments hype “free” speed and lower costs, while skeptics demand cold‑start checks and call out test choices—making this a big deal for cloud bills and dev sanity.
Rust on ARM64 just stole the show in AWS Lambda land, with the benchmark’s author finding it fastest and most cost‑friendly overall—helped by a ~20% price break on ARM. Even Python stirred drama: Python 3.11 on ARM edged out newer versions, while Node.js 22 on ARM beat older Node on x86. The tests cover CPU, memory, and light workloads, and the whole thing is open source on GitHub. New runtime shoutouts: Rust GA (Nov 14, 2025) and Python 3.14 GA (Nov 18, 2025).
Then the comments lit up. One reader slammed the TL;DR framing—“ARM64 is just strictly faster”—and accused the post of underselling the obvious speed win. Another nitpicked the CPU test, pointing out the SHA256 choice can ride special chip tricks, hinting the results might be less universal. Practical devs piled in with “real world” pain: cold starts (that first run delay) and the notorious Python “import boto3” library slog, demanding it be benchmarked because “it takes forever” on low‑memory Lambdas. Cost‑cutters cheered a “easiest hack” to cut AWS bills by switching to ARM, claiming “up to 50% lower” prices. And, of course, someone asked: where are the Linux ARM laptops? Cue memes of “free speed boosts” just by flipping architectures and side‑eye at methodology. Drama level: high, wallets excited, purists skeptical.
Key Points
- •Open-source benchmarks compared AWS Lambda arm64 vs. x86_64 across CPU, memory, and light workloads using Node.js, Python, and Rust.
- •Tests ran in AWS us-east-2 (Ohio) and covered 42 Lambda functions (7 runtimes × 2 architectures × 3 workloads).
- •Rust on arm64 was the overall performance and cost-efficiency winner; a 20% arm cost discount improved efficiency despite occasional x86_64 Rust wins.
- •Python 3.11 on arm64 slightly outperformed newer Python runtimes; Node.js 22 on arm64 was consistently faster in tests.
- •Benchmarks used outlier removal and percentile metrics, and included the GA Rust runtime (Nov 14, 2025) and Python 3.14 runtime (Nov 18, 2025); code and results are on GitHub.