[Bug] Anthropic API Error: 429 Rate Limit with Multiple Parallel Sessions Below Usage Cap

Bug Description
Unexpected 429 rate limit errors in Claude Code (Max plan).

I am running multiple Claude Code sessions (about 3 in parallel). Only one session works normally, while the others consistently return rate limit errors.

This is happening under normal usage:

• My total usage is only ~65% of the weekly cap
• I am not sending rapid or burst requests
• Usage is steady across sessions

The behavior seems inconsistent, as one session works fine while others are blocked with rate limits at the same time.

This does not appear to be normal RPM or token limit behavior and may indicate a bug or incorrect session-level throttling.

Please investigate potential issues with multi-session usage or account-level rate limiting.

Environment Info

• Platform: darwin
• Terminal: WarpTerminal
• Version: 2.1.98
• Feedback ID: 91434117-38aa-4379-9269-656fb321473d

Errors

[{"error":"Error: NON-FATAL: Lock acquisition failed for /Users/hyesungpark/.local/share/claude/versions/2.1.98 (expected in multi-process scenarios)\n    at BU_ (/$bunfs/root/src/entrypoints/cli.js:2810:2153)\n    at Ht6 (/$bunfs/root/src/entrypoints/cli.js:2810:1233)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-10T02:04:05.679Z"},{"error":"Error: 429 {\"type\":\"error\",\"error\":{\"type\":\"rate_limit_error\",\"message\":\"This request would exceed your account's rate limit. Please try again later.\"},\"request_id\":\"req_011CZuLQCeLX6FCcfoTzWZoc\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:52623)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:50:4943)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-10T02:53:57.833Z"}]