[BUG] Opus 4.8 regression now also hits Sonnet 4.6 — the "switch to Sonnet" workaround no longer works (June 22–23, 2026)

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?

Bug Description
Sustained, intermittent reasoning / instruction-following regression in Claude Code (CLI) and Cowork since ~June 14. NEW and important: as of June 22–23 it now affects Sonnet 4.6 as well as Opus 4.8, so the common "switch to Sonnet 4.6" workaround (e.g. #68657, Sonnet 0/180+) no longer holds for me. Same failure class on both models, in a FRESH session, with anti-hallucination rules explicitly loaded.

Symptom class (both models):

• ignores explicit, loaded rules (a top-of-file "verify before you claim" GATE)
• acts without being asked / out of scope
• concludes from stale/indirect data (e.g. tasklist, a missing file) instead of the live artifact
• false "done"/"fixed" claims; fake execution
• convoluted detours (writes a script to run git commit instead of running git)

Real damage: while "fixing" it, the agent nulled an AnimBlueprint's 3 animation references.

Environment

• Platform: Windows
• Claude Code: v2.1.186 (CLI) + Claude Cowork
• Models: Opus 4.8 AND Sonnet 4.6 (agents model: inherit)
• Effort: ultracode
• Setup: multi-agent orchestration (lead agent delegating to cpp / unreal / modeler / qa subagents)

Expected: agent follows its loaded rules and verifies state from the live artifact before claiming or acting.
Actual: ignores rules, concludes from indirect data, false success; "comes and goes" day to day.

Related / corroboration: #68780, #68657, #69065, #69398; status.claude.com logged Opus 4.8 elevated-error incidents June 13–23 (Sonnet+Opus ~10% on June 16). Support escalation in progress (Fin conv 215474811581681).

What Should Happen?

Claude shoud work normaly and give correct anwers

Error Messages/Logs

Steps to Reproduce

Just regular orqestra job

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.186

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_