Claude Code v2.1.154 → v2.1.156: Opus 4.8 thinking blocks fix (must-update if hitting API errors)

[claude-yolo]

WHY this matters

Opus 4.8 became the default model in v2.1.154. But it was corrupting thinking blocks — causing API errors for users who'd just upgraded. This is a must-update for anyone hitting unexplained API errors since the Opus 4.8 default rollout.

Also adds mid-conversation-system-2026-04-07 beta header support for mid-conversation system message updates in managed agents.

What changed

• v2.1.154 → v2.1.156 (two patch versions)
• Opus 4.8 thinking block corruption → fixed
• mid-conversation-system-2026-04-07 beta header added to managed agents API + thinking_tokens observability docs

See also

Docs PR: thevibeworks/claude-code-docs#994

/cc @lroolle