LM Studio — Anthropic Compatibility Endpoints

LM Studio exposes a /v1/messages endpoint that mirrors the Anthropic Messages API. Any code or tool that talks to Anthropic — including Claude Code and the Anthropic Python/JS SDK — can be redirected to a local LM Studio server with two env vars.

Supported Endpoints

Endpoint	Method
`/v1/messages`	POST

Quick Start — Claude Code with LM Studio

export ANTHROPIC_BASE_URL=http://localhost:1234
export ANTHROPIC_AUTH_TOKEN=lmstudio
claude --model openai/gpt-oss-20b

ANTHROPIC_BASE_URL — points Claude Code at the local server instead of api.anthropic.com
ANTHROPIC_AUTH_TOKEN — any non-empty string; LM Studio ignores the value unless auth is enabled
--model — pass the LM Studio model ID (e.g. ibm/granite-4-micro, openai/gpt-oss-20b)

Authentication

LM Studio accepts two auth header formats when Require Authentication is enabled:

Header	Value
`x-api-key`	`$LM_API_TOKEN`
`Authorization`	`Bearer $LM_API_TOKEN`

When auth is disabled, both headers are optional.

cURL Example

curl http://localhost:1234/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: $LM_API_TOKEN" \
  -d '{
    "model": "ibm/granite-4-micro",
    "max_tokens": 256,
    "messages": [
      {"role": "user", "content": "Write a haiku about local LLMs."}
    ]
  }'

Python SDK Example

from anthropic import Anthropic

client = Anthropic(
    base_url="http://localhost:1234",
    api_key="lmstudio",          # any string when auth is disabled
)

message = client.messages.create(
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello from LM Studio"}],
    model="ibm/granite-4-micro",
)
print(message.content)

api_key can be omitted entirely when Require Authentication is off
Drop-in replacement: only base_url changes vs. the real Anthropic API

Key Takeaways

LM Studio's /v1/messages is API-compatible with api.anthropic.com/v1/messages
Two env vars (ANTHROPIC_BASE_URL + ANTHROPIC_AUTH_TOKEN) are all that's needed to redirect Claude Code to a local model
Model IDs come from LM Studio, not Anthropic — use whatever is loaded in the LM Studio server
Auth is optional by default; enable it in LM Studio settings if the server is exposed beyond localhost
Any Anthropic SDK client (Python, JS, cURL) works without code changes beyond base_url

wiki/claude-code/headless-cli — running Claude Code non-interactively with -p
wiki/claude-code/overview — full product capabilities
wiki/llm-models/claude-model-catalog — official Anthropic model IDs for comparison
wiki/concepts/local-llm-serving — broader context on self-hosted model inference

Sources

LM Studio Docs: Anthropic Compatibility — raw/Anthropic Compatibility Endpoints.md

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