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Claude Opus 4.8 bug corrupts tool calls in Japanese environments

By PulseAugur Editorial · [1 sources] ·

A bug in Anthropic's Claude Opus 4.8 model can silently corrupt tool calls, particularly in Japanese environments and during long-running sessions. This corruption causes function arguments to appear as raw text and function tags to become nonsensical tokens, creating an self-reinforcing loop where the model imitates the corrupted output. The issue, which does not affect Opus 4.7, can be mitigated by downgrading to the previous version, decomposing tasks to keep sessions shorter, or using the `/compact` command to summarize history. AI

IMPACT This bug highlights potential risks in long-context models and the importance of task decomposition for reliable AI operation.

RANK_REASON A user-reported bug in a specific model version with detailed technical analysis and mitigation steps. [lever_c_demoted from research: ic=1 ai=1.0]

Read on dev.to — Claude Code tag →

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

Claude Opus 4.8 bug corrupts tool calls in Japanese environments

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0 / 100
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Tool
A user-reported bug in a specific model version with detailed technical analysis and mitigation steps. [lever_c_demoted from research: ic=1 ai=1.0]
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Only one publisher covered this so far. Single-source stories can still rank when the publisher is high-authority, but they lack cross-source corroboration.
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model release, safety
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High
Clearly on-topic for AI-industry coverage.
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127 days old
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COVERAGE [1]

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

    Claude Code (Opus 4.8) Silently Corrupts All Tool Calls — An Unfixed Bug Easy to Trigger in Japanese Environments

    <p>After running Claude Code on long, always-on sessions, you may suddenly find <strong>every tool call is broken</strong>. I hit this while running multiple sessions for hours in a Japanese environment. Here's what I found.</p> <h2> What happens </h2> <ul> <li>Function call open…

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