120 lines
3.6 KiB
Markdown
120 lines
3.6 KiB
Markdown
---
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title: "LM Studio — Anthropic Messages API"
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aliases: [lmstudio-messages, lm-studio-anthropic-messages]
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tags: [lmstudio, anthropic, api, messages, local-llm, streaming, tools]
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sources: [raw/Messages.md]
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created: 2026-04-30
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updated: 2026-04-30
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---
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# LM Studio — Anthropic Messages API
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The `/v1/messages` endpoint in LM Studio mirrors the Anthropic Messages API exactly — same request shape, same response shape. Use it as a local drop-in for any code already calling Anthropic's cloud API.
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## Endpoint
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```
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POST http://localhost:1234/v1/messages
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```
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Required headers:
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- `Content-Type: application/json`
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- `x-api-key: $LM_API_TOKEN` — optional if **Require Authentication** is disabled in LM Studio
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## Basic Request
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```bash
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curl http://localhost:1234/v1/messages \
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-H "Content-Type: application/json" \
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-H "x-api-key: $LM_API_TOKEN" \
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-d '{
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"model": "ibm/granite-4-micro",
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"max_tokens": 256,
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"messages": [
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{"role": "user", "content": "Say hello from LM Studio."}
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]
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}'
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```
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## Streaming
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Add `"stream": true` to receive Server-Sent Events (SSE):
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```bash
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curl http://localhost:1234/v1/messages \
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-H "Content-Type: application/json" \
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-H "x-api-key: $LM_API_TOKEN" \
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-d '{
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"model": "ibm/granite-4-micro",
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"messages": [{"role": "user", "content": "Hello"}],
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"max_tokens": 256,
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"stream": true
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}'
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```
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SSE event sequence:
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1. `message_start`
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2. `content_block_start`
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3. `content_block_delta` (repeating)
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4. `content_block_stop`
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5. `message_delta`
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6. `message_stop`
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## Tool Use
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Pass a `tools` array with JSON Schema input definitions and a `tool_choice` policy:
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```bash
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curl http://localhost:1234/v1/messages \
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-H "Content-Type: application/json" \
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-H "x-api-key: $LM_API_TOKEN" \
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-d '{
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"model": "ibm/granite-4-micro",
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"max_tokens": 1024,
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"tools": [
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{
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"name": "get_weather",
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"description": "Get the current weather in a given location",
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"input_schema": {
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"type": "object",
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"properties": {
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"location": {
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"type": "string",
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"description": "The city and state, e.g. San Francisco, CA"
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}
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},
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"required": ["location"]
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}
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}
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],
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"tool_choice": {"type": "any"},
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"messages": [
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{"role": "user", "content": "What is the weather like in San Francisco?"}
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]
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}'
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```
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`tool_choice` options (Anthropic-compat): `"auto"`, `"any"`, `{"type": "tool", "name": "…"}`.
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## Authentication
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| Scenario | Header needed |
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|----------|---------------|
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| Auth disabled in LM Studio | No `x-api-key` required |
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| Auth enabled | `x-api-key: $LM_API_TOKEN` |
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## Key Takeaways
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- `POST /v1/messages` on `localhost:1234` is a drop-in for `api.anthropic.com/v1/messages`
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- Same request body — swap the base URL and optionally add `x-api-key`
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- Streaming uses standard Anthropic SSE event names — existing stream parsers work unchanged
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- Tool use with `input_schema` / `tool_choice` is supported
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- Auth header is optional when LM Studio's **Require Authentication** is off
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- See [[wiki/claude-code/lmstudio-anthropic-compat|lmstudio-anthropic-compat]] for redirecting the full Anthropic SDK via env vars
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## Related
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- [[wiki/claude-code/lmstudio-anthropic-compat|LM Studio Anthropic Compat Setup]] — redirect Claude Code / SDK to local server
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- [[wiki/claude-code/lmstudio-chat-completions|LM Studio Chat Completions]] — OpenAI-compatible `/v1/chat/completions`
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- [[wiki/claude-code/lmstudio-rest-api|LM Studio REST API]] — native v1 endpoints and feature comparison table
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- [[wiki/claude-code/lmstudio-idle-ttl-auto-evict|Idle TTL & Auto-Evict]] — memory management for loaded models
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