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Claude Code 2.1.285 places server instructions in user turns, not system prompts

By PulseAugur Editorial · [1 sources] ·

A recent analysis of Claude Code 2.1.285 revealed that server instructions, intended to guide the AI's behavior, are not consistently placed in the system prompt as expected. Instead, these instructions are often delivered as a system reminder within the first user turn, and are truncated at 2,048 characters. This behavior was observed across multiple runs, with the instructions arriving in a user turn rather than during the initial handshake, and the character limit impacting the delivery of critical information. AI

IMPACT This behavior change in Claude Code may affect how developers integrate custom instructions and tools, potentially requiring adjustments to their server implementations.

RANK_REASON Analysis of a specific version of a product (Claude Code) detailing its behavior with a particular feature (MCP server instructions).

Read on dev.to — MCP tag →

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

Claude Code 2.1.285 places server instructions in user turns, not system prompts

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32 / 100
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Tool
Analysis of a specific version of a product (Claude Code) detailing its behavior with a particular feature (MCP server instructions).
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Single-source cluster
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product
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High
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Breaking (< 6h)
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COVERAGE [1]

  1. dev.to — MCP tag TIER_1 English(EN) · Rulestack ·

    Where Claude Code puts your MCP server's instructions: in a user turn, not the system prompt, cut at 2,048 characters

    <blockquote> <p>20 of 20 <code>claude -p</code> runs on Claude Code 2.1.285 opened our stdio MCP server with <code>server/discover</code>, a probe the docs say stdio servers only get when <code>MCP_PROTOCOL_NEGOTIATION=auto</code> is set, and in the 2 runs where the server answer…

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