[BUG] ECONNRESET "Connection dropped" with claude-fable-5-1 at normal effort; works at MAX

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?

In one project, almost every session fails with "API Error: Connection dropped (ECONNRESET)".
The project pins "model": "claude-fable-5-1" in .claude/settings.json.
Other projects on the same machine (default model) work normally.
If I switch the same project to Fable 5.1 MAX, the error does not happen, but running at MAX is not viable because of token/usage cost.

[BUG] ECONNRESET "Connection dropped" only with claude-fable-5-1 at normal effort; same project works at MAX

Environment

• Claude Code 2.1.280 (npm-global), Windows 11 x64, VS Code integrated terminal
• claude doctor: no installation issues
• Feedback ID: <cole aqui>

Problem
In one project, almost every session fails with API Error: Connection dropped (ECONNRESET).
The project pins "model": "claude-fable-5-1" in .claude/settings.json.
Other projects on the same machine (default model) work normally.

Key observation

• claude-fable-5-1 (normal effort) → frequent ECONNRESET
• claude-fable-5-1 with MAX <effort / 1M context — confirmar> → no errors

Same machine, same network, same project, same session setup. Only the model setting changes.
Running at MAX just to avoid the error is not viable (token cost).

Already ruled out

• Rebooted PC; switched to a different router/ISP: error persists
• No proxy (netsh winhttp show proxy = direct), no proxy env vars
• Test-NetConnection api.anthropic.com -Port 443 → TcpTestSucceeded True
• NODE_OPTIONS=--dns-result-order=ipv4first, CLAUDE_CODE_MAX_RETRIES=25, raised API_TIMEOUT_MS / CLAUDE_STREAM_IDLE_TIMEOUT_MS: no effect
• Updated from 2.1.201 to 2.1.280: no effect

Possibly related
#86473, #94225, #96070, #95616. Status page on 2026-09-22 listed elevated errors for Fable 5/5.1.

Expected
Fable 5.1 at normal effort should be as stable as the MAX configuration.

What Should Happen?

Claude Code with claude-fable-5-1 at normal effort should keep the connection and finish responses, like it does at MAX or with other models.

Error Messages/Logs

API Error: Connection dropped (ECONNRESET)

Steps to Reproduce

1. On Windows 11, open a project whose .claude/settings.json contains "model": "claude-fable-5-1"
2. Start a new session with claude and ask for a normal coding task (read files, edit code, run dotnet build)
3. After one or a few turns the response stops with "API Error: Connection dropped (ECONNRESET)"
4. Switch the same project/session setup to Fable 5.1 MAX → no error
5. Other projects using the default model on the same machine → no error

Already ruled out: PC reboot, different router/ISP, no proxy (netsh winhttp = direct),
Test-NetConnection api.anthropic.com:443 OK, NODE_OPTIONS=--dns-result-order=ipv4first,
CLAUDE_CODE_MAX_RETRIES=25, raised API_TIMEOUT_MS / CLAUDE_STREAM_IDLE_TIMEOUT_MS,
update from 2.1.201 to 2.1.280, claude doctor reports no issues.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.280 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Feedback ID: <cole o ID do /feedback>
Possibly related: #86473, #94225, #96070, #95616
Status page on 2026-09-22 listed elevated errors for Fable 5 / 5.1.
Project also has a DevSquad setup (27 skills, 27 agents, 4 small SessionStart hooks).