Announcement

Experimental Bun + JSC build reportedly gives Claude Code’s CLI 24% faster startup

The preview’s author claims 48% lower memory use and 46% lower CPU use, but nearly twice the binary size.

1 Source, 20d ago, first seen 20d ago

Bun AoT
VS
Bun JIT
Claude Code, same source, same 5-turn session. AoT runs with the JIT off.
Time to interactive
165 ms
216 ms
-24%
Wall time
launch + 5 turns
322 ms
529 ms
-39%
CPU time
Memory at interactive
395 ms
738 ms
-46%
56 MB
108 MB
-48%

Memory after 5 turns
82 MB
159 MB
-48%
101 MB
Peak memory
Executable size target: +100 MB at most
194 MB
-48%
430 MB
229 MB
+88%
Early prototype, macoS arm64. Medians of 8 runs against a fake API server on one MacBook Pro. Memory is phys_footprint. CPU is user + system, all threads. Turns in the JIT build are not CPU bound, so part of the wall time gap is waiting. 28 Sep 2026.

TLDR

An early preview of experimental Bun + JSC with ahead-of-time compilation reports 24% faster startup, 48% lower memory use and 46% lower CPU use for Claude Code’s CLI, alongside a binary nearly twice as large. The author later pointed to TS 6 vs TS 7 for benchmarking because it has a close Go implementation of the same code.

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1 Source, first seen 20d ago