Anthropic Bun Fork Native String Replacement
- Entity ID:
ent-20260419-a7b8c9d0e1f2 - Type:
service - Scope:
shared - Status:
active - Aliases: bun fork sentinel replacer, post-serialization TLS layer string swap, native cch replacer
Description
Anthropic's custom Bun fork that ships with the standalone Claude Code binary contains a native-layer string replacement modifying the JSON request body AFTER serialization but BEFORE TLS encryption. The native patch targets the billing attribution sentinel 'cch=24b72' and replaces it with a 5-character hash. When the hash mismatches the server-side cached prompt sentinel, cache lookups miss and the request is re-billed at full rate. Only the standalone binary is affected; running via 'npx @anthropic-ai/claude-code' uses Node and sidesteps the replacement.
Key claims
- Anthropic adopts expertise-stratified weapons-uplift threshold framework
- Bun fork mutates request body between JSON serialize and TLS encrypt, breaking prompt cache
Relations
- Anthropic Bun Fork Native String Replacement --[contains]--> Two-Version Output Efficiency Directive
- Anthropic Bun Fork Native String Replacement --[caused]--> Billing Sentinel Bug (cch=00000)
- Anthropic Bun Fork Native String Replacement --[depends_on]--> Bun Runtime