HTTP 529 Overloaded errors occurring frequently on Max plan with Claude Opus 4.6

Summary

Frequent HTTP 529 Overloaded errors occurring during active Claude Code sessions on a Claude Max plan, which is supposed to have priority access. This is causing significant workflow disruption.

Error Details

{
  "type": "error",
  "error": {
    "type": "overloaded_error",
    "message": "Overloaded. https://docs.claude.com/en/api/errors"
  },
  "request_id": "req_011CZTJ1qxC36noVwkn5tcvj"
}

HTTP Status Code: 529

Environment

| Field | Value |
|-------|-------|
| Claude Code Version | 2.1.84 |
| OS | macOS Darwin 25.3.0 (ARM64, Apple Silicon M1 Pro) |
| Model | claude-opus-4-6 |
| Plan | Claude Max |
| Date | 2026-03-27 |
| Shell | zsh |

Reproduction

1. Open Claude Code on Max plan with claude-opus-4-6 model
2. Run a session with tool use (MCP servers, file reads, bash commands)
3. Error occurs mid-session — no consistent repro pattern, appears random

Frequency

Very frequent — occurring multiple times per day across different sessions. Not an isolated incident.

Impact

• Interrupts active development sessions mid-flow
• Affects productivity despite paying for Max plan priority access
• Occurs even in sessions with moderate tool use (not just heavy parallel agent workloads)

Additional Context

• Running multiple Claude Code sessions simultaneously (common workflow)
• Using MCP servers: XcodeBuildMCP, Playwright, Figma, sequential-thinking, shadcn, Sentry, Vercel, Supabase
• Running on Apple Silicon (M1 Pro) with macOS 15.3
• The error has been increasing in frequency around 2026-03-26/27, potentially correlated with high server demand following the Claude Mythos/Capybara model leak news

Expected Behavior

Max plan subscribers should experience significantly reduced overload errors compared to free/lower tiers. Priority access should buffer against server capacity constraints.

Workaround Attempted

• Retry on error (transient fix)
• Reduce parallel sessions (helps slightly)
• --fallback-model sonnet is only available in --print mode, not interactive sessions — a settings-level fallback model config would be highly valuable

Feature Request (related)

Please consider adding a fallbackModel setting to settings.json so interactive sessions can automatically fall back to a less-loaded model (e.g., Sonnet) when Opus returns a 529, rather than failing hard. The --fallback-model CLI flag currently only works with --print mode.

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Reported by: AMBR0SI0 via Claude Code CLI