[MODEL] Fable 5 Ultracode spawns excessive parallel agents for single refactoring task

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Other unexpected behavior

What You Asked Claude to Do

Run a small refactoring task on using Fable 5 with Ultracode mode enabled.

What Claude Actually Did

What Claude Actually Did

1. Fable 5 spawned 7 parallel agents for a single refactoring task
2. Agent 1 consumed 139.9k tokens
3. Agent 2 consumed 108.7k tokens
4. Agents 3-5 consumed 77-91k tokens each
5. Agent 6 consumed 90.4k tokens
6. Agent 7 consumed 128.6k tokens
7. Total consumption: 716.6k tokens in 5m 35s
8. Session quota jumped from 33% → 82% in single workflow, then to 90% total

Expected Behavior

Fable 5 should spawn agents conservatively and proportionally to task complexity, similar to Opus 4.8 and other models. A single refactoring task should not require 7 parallel agents. Quota consumption should be proportional to actual work performed.

Files Affected

No unexpected file modifications observed

Permission Mode

Accept Edits was ON (auto-accepting changes)

Can You Reproduce This?

Yes, every time with the same prompt

Steps to Reproduce

1. Open Claude Code app on Windows
2. Set model to Fable 5 with Ultracode mode enabled
3. Request a refactoring task (e.g., "Refactor map-composer-subsystem")
4. Observe agent spawning behavior in real-time
5. Check /usage to see token consumption breakdown

Claude Model

Other

Relevant Conversation

Fable 5 spawned agents without explicit instruction to do so. The model appears to be over-interpreting task complexity and creating unnecessary parallel workers.

Impact

Low - Minor inconvenience

Claude Code Version

1.11847.5 (9692f0) 2026-06-09T17:34:27.000Z

Platform

Anthropic API

Additional Context

High Quota consumption is disproportionate to work performed. Same task on Opus 4.8 consumed ~1M tokens but only used 33% of quota. Fable 5 consumed 716.6k tokens and used 49% of quota in a single workflow.

Pattern observed:

Fable 5 with Ultracode mode consistently spawns excessive parallel agents
Opus 4.8 with Ultracode mode does NOT spawn 7 agents on the same task type
This behavior is specific to Fable 5 and appears to be a model-level decision, not a configuration issue

<img width="573" height="246" alt="Image" src="https://github.com/user-attachments/assets/a1fa7c08-0784-4067-ac43-c85f86a4c4c4" />