Cowork on Windows crashes with "Illegal instruction" / exit code 3 — Bun/Claude Code binary requires AVX not exposed by Hyper-V VM
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?
Título: Cowork on Windows crashes with "Illegal instruction" / exit code 3 — Bun/Claude Code binary requires AVX not exposed by Hyper-V VM
Descripción:
Cowork fails on every session attempt with Claude Code process exited with code 3. The VM itself starts up successfully and connects to the API — the crash happens specifically when the Claude Code binary starts inside the guest.
Environment:
Claude Desktop version: 1.30096.5.0 (MSIX)
OS: Windows 11 (nueva instalación)
Cowork bundle version: 6d1538ba6fecc4e5c5583993c4b30bb1875f0f5a
Claude Code SDK version: 2.1.229
CPU: (pegar aquí el resultado del comando anterior)
Reproduction steps:
Open Claude Desktop → Cowork
Wait for VM to start (completes successfully, ~50s)
Send any message to start a session
Session immediately fails with progress bar disappearing at ~30-35%
Relevant log excerpt (main.log):
panic: Illegal instruction at address 0x7FF6C80408D4
panicked during a panic. Aborting.
Claude Code process exited with code 3
Root cause (from prior GitHub issues #19967, #19981, #57053): Bun runtime bundled with Claude Code selects/uses AVX instructions that the host CPU or the Hyper-V virtual CPU doesn't expose, causing an immediate illegal-instruction crash before any session can run.
Additional context: Prior to this, encountered "Missing HCS services" errors, resolved by enabling Hyper-V/VMP/Containers + repairing a corrupted vfpext.sys via sfc /scannow. VM startup itself now works cleanly (network, plan9 shares, API reachability all confirmed in cowork-service.log and cowork_vm_node.log). This is a distinct, separate issue from the crash described here.
What Should Happen?
Título: Cowork on Windows crashes with "Illegal instruction" / exit code 3 — Bun/Claude Code binary requires AVX not exposed by Hyper-V VM
Descripción:
Cowork fails on every session attempt with Claude Code process exited with code 3. The VM itself starts up successfully and connects to the API — the crash happens specifically when the Claude Code binary starts inside the guest.
Environment:
Claude Desktop version: 1.30096.5.0 (MSIX)
OS: Windows 11 (nueva instalación)
Cowork bundle version: 6d1538ba6fecc4e5c5583993c4b30bb1875f0f5a
Claude Code SDK version: 2.1.229
CPU: (pegar aquí el resultado del comando anterior)
Reproduction steps:
Open Claude Desktop → Cowork
Wait for VM to start (completes successfully, ~50s)
Send any message to start a session
Session immediately fails with progress bar disappearing at ~30-35%
Relevant log excerpt (main.log):
panic: Illegal instruction at address 0x7FF6C80408D4
panicked during a panic. Aborting.
Claude Code process exited with code 3
Root cause (from prior GitHub issues #19967, #19981, #57053): Bun runtime bundled with Claude Code selects/uses AVX instructions that the host CPU or the Hyper-V virtual CPU doesn't expose, causing an immediate illegal-instruction crash before any session can run.
Additional context: Prior to this, encountered "Missing HCS services" errors, resolved by enabling Hyper-V/VMP/Containers + repairing a corrupted vfpext.sys via sfc /scannow. VM startup itself now works cleanly (network, plan9 shares, API reachability all confirmed in cowork-service.log and cowork_vm_node.log). This is a distinct, separate issue from the crash described here.
Error Messages/Logs
Título: Cowork on Windows crashes with "Illegal instruction" / exit code 3 — Bun/Claude Code binary requires AVX not exposed by Hyper-V VM
Descripción:
Cowork fails on every session attempt with Claude Code process exited with code 3. The VM itself starts up successfully and connects to the API — the crash happens specifically when the Claude Code binary starts inside the guest.
Environment:
Claude Desktop version: 1.30096.5.0 (MSIX)
OS: Windows 11 (nueva instalación)
Cowork bundle version: 6d1538ba6fecc4e5c5583993c4b30bb1875f0f5a
Claude Code SDK version: 2.1.229
CPU: (pegar aquí el resultado del comando anterior)
Reproduction steps:
Open Claude Desktop → Cowork
Wait for VM to start (completes successfully, ~50s)
Send any message to start a session
Session immediately fails with progress bar disappearing at ~30-35%
Relevant log excerpt (main.log):
panic: Illegal instruction at address 0x7FF6C80408D4
panicked during a panic. Aborting.
Claude Code process exited with code 3
Root cause (from prior GitHub issues #19967, #19981, #57053): Bun runtime bundled with Claude Code selects/uses AVX instructions that the host CPU or the Hyper-V virtual CPU doesn't expose, causing an immediate illegal-instruction crash before any session can run.
Additional context: Prior to this, encountered "Missing HCS services" errors, resolved by enabling Hyper-V/VMP/Containers + repairing a corrupted vfpext.sys via sfc /scannow. VM startup itself now works cleanly (network, plan9 shares, API reachability all confirmed in cowork-service.log and cowork_vm_node.log). This is a distinct, separate issue from the crash described here.Steps to Reproduce
Título: Cowork on Windows crashes with "Illegal instruction" / exit code 3 — Bun/Claude Code binary requires AVX not exposed by Hyper-V VM
Descripción:
Cowork fails on every session attempt with Claude Code process exited with code 3. The VM itself starts up successfully and connects to the API — the crash happens specifically when the Claude Code binary starts inside the guest.
Environment:
Claude Desktop version: 1.30096.5.0 (MSIX)
OS: Windows 11 (nueva instalación)
Cowork bundle version: 6d1538ba6fecc4e5c5583993c4b30bb1875f0f5a
Claude Code SDK version: 2.1.229
CPU: (pegar aquí el resultado del comando anterior)
Reproduction steps:
Open Claude Desktop → Cowork
Wait for VM to start (completes successfully, ~50s)
Send any message to start a session
Session immediately fails with progress bar disappearing at ~30-35%
Relevant log excerpt (main.log):
panic: Illegal instruction at address 0x7FF6C80408D4
panicked during a panic. Aborting.
Claude Code process exited with code 3
Root cause (from prior GitHub issues #19967, #19981, #57053): Bun runtime bundled with Claude Code selects/uses AVX instructions that the host CPU or the Hyper-V virtual CPU doesn't expose, causing an immediate illegal-instruction crash before any session can run.
Additional context: Prior to this, encountered "Missing HCS services" errors, resolved by enabling Hyper-V/VMP/Containers + repairing a corrupted vfpext.sys via sfc /scannow. VM startup itself now works cleanly (network, plan9 shares, API reachability all confirmed in cowork-service.log and cowork_vm_node.log). This is a distinct, separate issue from the crash described here.
Claude Model
None
Is this a regression?
Yes, this worked in a previous version
Last Working Version
_No response_
Claude Code Version
3
Platform
Anthropic API
Operating System
Windows
Terminal/Shell
Windows Terminal
Additional Information
Título: Cowork on Windows crashes with "Illegal instruction" / exit code 3 — Bun/Claude Code binary requires AVX not exposed by Hyper-V VM
Descripción:
Cowork fails on every session attempt with Claude Code process exited with code 3. The VM itself starts up successfully and connects to the API — the crash happens specifically when the Claude Code binary starts inside the guest.
Environment:
Claude Desktop version: 1.30096.5.0 (MSIX)
OS: Windows 11 (nueva instalación)
Cowork bundle version: 6d1538ba6fecc4e5c5583993c4b30bb1875f0f5a
Claude Code SDK version: 2.1.229
CPU: (pegar aquí el resultado del comando anterior)
Reproduction steps:
Open Claude Desktop → Cowork
Wait for VM to start (completes successfully, ~50s)
Send any message to start a session
Session immediately fails with progress bar disappearing at ~30-35%
Relevant log excerpt (main.log):
panic: Illegal instruction at address 0x7FF6C80408D4
panicked during a panic. Aborting.
Claude Code process exited with code 3
Root cause (from prior GitHub issues #19967, #19981, #57053): Bun runtime bundled with Claude Code selects/uses AVX instructions that the host CPU or the Hyper-V virtual CPU doesn't expose, causing an immediate illegal-instruction crash before any session can run.
Additional context: Prior to this, encountered "Missing HCS services" errors, resolved by enabling Hyper-V/VMP/Containers + repairing a corrupted vfpext.sys via sfc /scannow. VM startup itself now works cleanly (network, plan9 shares, API reachability all confirmed in cowork-service.log and cowork_vm_node.log). This is a distinct, separate issue from the crash described here.
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