How to run Claude Code with the full system prompt on custom Bedrock or Vertex model names

Since Claude Code 2.1.312, on Bedrock, Vertex, Foundry and Mantle a model name Claude Code doesn't recognize, such as a custom deployment name or an inference profile ARN, gets the shorter system prompt. That holds even when Sonnet or Haiku sits behind it. The shorter prompt is the version with abbreviated tool descriptions. To run the full prompt instead, set the environment variable to 0.

export CLAUDE_CODE_SIMPLE_SYSTEM_PROMPT=0

To keep it that way, add it to the env block of settings.json.

{
  "env": {
    "CLAUDE_CODE_SIMPLE_SYSTEM_PROMPT": "0"
  }
}

false, no and off work in place of 0. Setting 1 does the opposite and uses the shorter prompt on any model. Either way the tool set, hooks, MCP servers and CLAUDE.md discovery stay the same.