Messages API (Anthropic-compatible)

POST /v1/messages implements Anthropic’s Messages API shape. If your code already speaks that format — through the Anthropic SDK or a hand-rolled client — you can switch the base URL to Mesh and keep the rest of the integration unchanged.

The endpoint is not restricted to Anthropic models. Any model this gateway serves is reachable through it, so an existing Anthropic client can call an OpenAI, Google, or open-weight model without changing its request shape.

For new code, /v1/chat/completions remains the recommended entry point — it has the widest feature coverage.

Authentication

Both header styles are accepted:

x-api-key: rsk_YOUR_KEY

Authorization: Bearer rsk_YOUR_KEY

The x-api-key form is what Anthropic’s own SDKs send, which is why an unmodified client works once the base URL is pointed at Mesh.

Basic request

curl
Python (Anthropic SDK)
Node.js (Anthropic SDK)

curl https://api.meshapi.ai/v1/messages \
  -H "x-api-key: rsk_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-4.6",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Explain retrieval-augmented generation in two sentences."}
    ]
  }'

from anthropic import Anthropic

client = Anthropic(
    api_key="rsk_YOUR_KEY",
    base_url="https://api.meshapi.ai",
)

message = client.messages.create(
    model="anthropic/claude-sonnet-4.6",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Explain retrieval-augmented generation in two sentences."}
    ],
)
print(message.content[0].text)

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: "rsk_YOUR_KEY",
  baseURL: "https://api.meshapi.ai",
});

const message = await client.messages.create({
  model: "anthropic/claude-sonnet-4.6",
  max_tokens: 1024,
  messages: [
    { role: "user", content: "Explain retrieval-augmented generation in two sentences." },
  ],
});
console.log(message.content[0].text);

Streaming

Set stream: true for Anthropic’s SSE event sequence — message_start, content_block_start, content_block_delta, content_block_stop, message_delta, message_stop. Anthropic’s SDKs consume it unchanged.

with client.messages.stream(
    model="anthropic/claude-sonnet-4.6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Count to five."}],
) as stream:
    for text in stream.text_stream:
        print(text, end="")

Token counts arrive on message_delta, not message_start. Anthropic reports input tokens on the first frame; Mesh only knows them once the upstream response completes, so message_start.usage carries zeros and message_delta.usage carries the real figures. SDKs that accumulate usage across the stream end up with the correct totals.

Request fields

Field	Required	Notes
`model`	Yes	Any model in the Mesh catalog, in `provider/model-name` form
`max_tokens`	Yes	Maximum tokens to generate — required by the Anthropic shape
`messages`	Yes	`user` / `assistant` turns. A `system` turn is also accepted and keeps its position in the conversation
`system`	No	System prompt, passed as a top-level field rather than a message
`temperature`	No	Sampling temperature
`top_p`	No	Nucleus sampling
`top_k`	No	Accepted for compatibility, but not forwarded — no provider mapping today
`stop_sequences`	No	Strings that halt generation
`stream`	No	`true` for SSE — see Streaming
`thinking`	No	Accepted for compatibility, but not forwarded yet
`tools` / `tool_choice`	No	Anthropic-shaped tool definitions — see Tool Calling
`metadata`	No	`metadata.user_id` is recorded as the end-user identifier on the usage row. Not echoed back

Which endpoint should I use?

Use case	Endpoint
New integration, widest feature coverage	`/v1/chat/completions`
Existing Anthropic SDK code you don’t want to rewrite	`/v1/messages`
Claude Code	`/v1/messages`
Reasoning effort, hosted tools, background jobs	`/v1/responses`
Streaming output	either — both support SSE

Claude Code — point the CLI at Mesh
Tool Calling — the function-calling cycle
Responses API — reasoning effort and hosted tools
Available Models — every model this endpoint can reach

Introduction

Accounts & Access

Core Inference

Retrieval & Search

Multimodal

Operations

Mesh CLI

Platform

Reference

Messages API (Anthropic-compatible)

Authentication

Basic request

Streaming

Request fields

Which endpoint should I use?

​Authentication

​Basic request

​Streaming

​Request fields

​Which endpoint should I use?

​Related

Authentication

Basic request

Streaming

Request fields

Which endpoint should I use?

Related