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Use Claude Code with NIM#

Claude Code can use NIM as its backend through the Anthropic-compatible /v1/messages endpoint. For request and response details, refer to Messages (Anthropic-compatible).

Before You Begin#

Start a NIM deployment that serves a chat-capable model. For deployment instructions, refer to the Quickstart.

Note

Claude Code requires tool calling. Verify that your model supports tool use before you rely on it with Claude Code. For instructions and troubleshooting, refer to Tool Calling and MCP Integration.

To find the active model name and export it as MODEL_NAME, refer to Examples. The examples below use this variable.

Configure Claude Code#

Set the Claude Code environment variables to point to your NIM deployment:

export ANTHROPIC_BASE_URL="http://${NIM_ENDPOINT}:${NIM_SERVER_PORT}"
export ANTHROPIC_API_KEY="not-used"
export ANTHROPIC_CUSTOM_MODEL_OPTION="${MODEL_NAME}"
claude

Replace NIM_ENDPOINT with the hostname or IP address of your NIM deployment. Replace NIM_SERVER_PORT with the port, which is 8000 by default.

NIM does not validate ANTHROPIC_API_KEY. Set it to any non-empty string that satisfies Claude Code or the Anthropic SDK client.

ANTHROPIC_CUSTOM_MODEL_OPTION adds the model to the Claude Code /model picker. For additional options such as ANTHROPIC_CUSTOM_MODEL_OPTION_NAME and ANTHROPIC_CUSTOM_MODEL_OPTION_DESCRIPTION, refer to the Claude Code model configuration documentation.

This setting adds a custom entry, but it does not replace Claude Code built-in aliases such as haiku, sonnet, and opus. To map those aliases to the same model that NIM serves, set the alias variables explicitly:

export ANTHROPIC_API_KEY="not-used"
export ANTHROPIC_BASE_URL="http://${NIM_ENDPOINT}:${NIM_SERVER_PORT}"
export ANTHROPIC_CUSTOM_MODEL_OPTION="${MODEL_NAME}"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="${MODEL_NAME}"
export ANTHROPIC_DEFAULT_OPUS_MODEL="${MODEL_NAME}"
export ANTHROPIC_DEFAULT_SONNET_MODEL="${MODEL_NAME}"
export CLAUDE_CODE_SUBAGENT_MODEL="${MODEL_NAME}"

Troubleshooting#

This section covers common issues when Claude Code or other Anthropic-compatible clients connect to NIM through /v1/messages.

Claude Code Returns a Model `404` Error#

Symptoms

Claude Code appears to connect, but NIM logs contain errors such as the following:

The model 'claude-haiku-4-5-20251001' does not exist

Cause

Claude Code can continue to use built-in aliases such as haiku, sonnet, or opus for background functionality even after you add a custom model option. If those aliases still resolve to Anthropic model IDs, NIM returns 404 Not Found because it does not serve those model names.

Resolution

Map the Claude Code aliases to the same model name that NIM serves. To find the active model name and export it as MODEL_NAME, refer to Examples.

export ANTHROPIC_API_KEY="not-used"
export ANTHROPIC_BASE_URL="http://${NIM_ENDPOINT}:${NIM_SERVER_PORT}"
export ANTHROPIC_CUSTOM_MODEL_OPTION="${MODEL_NAME}"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="${MODEL_NAME}"
export ANTHROPIC_DEFAULT_OPUS_MODEL="${MODEL_NAME}"
export ANTHROPIC_DEFAULT_SONNET_MODEL="${MODEL_NAME}"
export CLAUDE_CODE_SUBAGENT_MODEL="${MODEL_NAME}"