[BUG] Memory leak during API response streaming - 1GB/second growth rate causes 20GB+ allocation

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?

Memory growth captured every 3 seconds via monitoring script:

16:17:12 - 604MB RSS (stable for 60+ seconds prior)
16:17:27 - 604MB RSS (stream processing begins)
16:17:30 - 1,689MB RSS (+1,085MB in 3s)
16:17:33 - 4,410MB RSS (+2,721MB in 3s)
16:17:36 - 7,267MB RSS (+2,857MB in 3s)
16:17:39 - 9,742MB RSS (+2,475MB in 3s)

Physical footprint reached 20.8GB before manual termination. Process remained in running state (R+), not crashed - memory just kept growing.

What Should Happen?

Memory should remain bounded during API response streaming. Response chunks should be processed and freed incrementally.

Error Messages/Logs

No error messages produced. The process continued running (state R+) while allocating 
unbounded memory. Had to be manually killed.

Relevant debug log output before memory explosion:


2026-01-20T00:16:59.421Z [DEBUG] Getting matching hook commands for SubagentStart with query: project-manager
2026-01-20T00:17:12.219Z [DEBUG] [API:request] Creating client
2026-01-20T00:17:12.220Z [DEBUG] [API:auth] OAuth token check complete
2026-01-20T00:17:14.209Z [DEBUG] Stream started - received first chunk


Debug logging stopped after stream started. No errors logged during the memory leak.

Memory monitoring output showing the leak:


16:17:27 - 604MB RSS
16:17:30 - 1,689MB RSS
16:17:33 - 4,410MB RSS
16:17:36 - 7,267MB RSS
16:17:39 - 9,742MB RSS


Physical footprint at termination: 20.8GB

Steps to Reproduce

1. Create a custom subagent that uses extended thinking (model: opus)
2. Invoke the subagent via Task tool
3. Wait for API response stream to begin
4. Observe memory growth ~13 seconds after stream starts

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.12

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Final output of the CLI

⏺ project-manager(Orchestrate todo-cli development)
  ⎿  Search(pattern: "/Users/haydenwaisanen/dev/todo-cli/**/*")
     Found 59 files
     tech-lead(Design technical architecture for todo-cli application)
     +9 more tool uses (ctrl+o to expand)
     ctrl+b to run in background

✻ Skedaddling… (ctrl+c to interrupt · 1m 1s · ↓ 2.6k tokens)

──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
❯
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  ? for shortcuts
Aborted()