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Claude Code hotfix resolves Opus 4.8 thinking block corruption bug

By PulseAugur Editorial · [1 sources] ·

A critical bug affecting Claude Code v2.1.154 and v2.1.155 has been resolved with the release of v2.1.156. The issue involved the mutation of 'thinking blocks' during multi-turn sessions when using the Opus 4.8 model with extended thinking enabled. This mutation caused silent payload corruption, leading to HTTP 400 errors from the Anthropic API and breaking agentic workflows. The hotfix ensures that signed thinking blocks are replayed byte-for-byte without modification, preventing these errors. AI

IMPACT Ensures stability for users of Claude Code with Opus 4.8, preventing workflow disruptions.

RANK_REASON This is a hotfix for a specific software tool, not a new model release or major product update.

Read on dev.to — Claude Code tag →

AI-generated summary · Google Gemini · from 1 sources. How we write summaries →

Claude Code hotfix resolves Opus 4.8 thinking block corruption bug

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This is a hotfix for a specific software tool, not a new model release or major product update.
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COVERAGE [1]

  1. dev.to — Claude Code tag TIER_1 English(EN) · Creeta ·

    Claude Code v2.1.156: Opus 4.8 Thinking Block Hotfix Explained

    <h2> What Broke: Thinking Block Corruption on Opus 4.8 </h2> <p>Claude Code v2.1.154 , released May 28, 2026, made Opus 4.8 the default model — and immediately surfaced a silent payload bug. Thinking blocks were being mutated during retry or multi-turn sequences, causing the Anth…

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