[BUG] Claude Code 2.1.x crashes with "Illegal instruction" on non-AVX CPUs (regression from 2.0.76)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code 2.1.15 crashes immediately on pasting the validation code to log in with an "Illegal instruction" error on CPUs without AVX support. The bundled Bun 1.3.6 selects the "baseline" build (which should work without AVX) but still executes AVX instructions.

What Should Happen?

Claude Code should run on x86-64-v2 CPUs without AVX, as it did in version 2.0.76.

Error Messages/Logs

CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x4001FB4
oh no: Bun has crashed. This indicates a bug in Bun, not your code.


Full crash output:

============================================================
Bun v1.3.6 (d530ed99) Linux x64 (baseline)
Linux Kernel v6.12.63 | glibc v2.41
CPU: sse42 popcnt
Args: "claude"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(22) http_server jsc no_avx2 no_avx spawn(5) standalone_executable process_dlopen
Builtins: "bun:main" "node:assert" "node:async_hooks" "node:buffer" "node:child_process" "node:constants" "node:crypto" "node:domain" "node:events" "node:fs" "node:fs/promises" "node:http" "node:https" "node:module" "node:net" "node:os" "node:path" "node:path/posix" "node:path/win32" "node:perf_hooks" "node:process" "node:querystring" "node:stream" "node:timers/promises" "node:tls" "node:tty" "node:url" "node:util" "node:zlib" "node:worker_threads" "undici" "ws" "node-fetch" "node:inspector" "node:http2" "node:diagnostics_channel"
Elapsed: 34184ms | User: 4183ms | Sys: 1074ms
RSS: 1.08GB | Peak: 0.44GB | Commit: 1.08GB | Faults: 0 | Machine: 16.78GB
CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x4001FB4
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Steps to Reproduce

1. Set up a VM or machine with a CPU that lacks AVX (e.g., Proxmox VM with x86-64-v2-AES CPU type)
2. Install Debian 13
3. Install Claude Code: curl -fsSL https://claude.ai/install.sh | bash
4. Run claude
5. Select login
6. Visit generated URL
7. Paste code

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.0.76

Claude Code Version

2.1.15

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

Environment:

• Proxmox VM with CPU type x86-64-v2-AES (no AVX)
• CPU flags: fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni ssse3 cx16 sse4_1 sse4_2 x2apic popcnt aes hypervisor lahf_lm cpuid_fault pti

Workaround:
Downgrading to 2.0.76 resolves the issue:

rm -rf ~/.local/share/claude ~/.local/bin/claude
curl -fsSL https://claude.ai/install.sh | bash -s 2.0.76

Related:

• Closed issue #13894 (similar AVX crash, but on different hardware)
• This appears to be a regression in the bundled Bun version between 2.0.76 and 2.1.x