> ## Documentation Index > Fetch the complete documentation index at: https://developers.telnyx.com/llms.txt > Use this file to discover all available pages before exploring further. # Anthropic API Migration Guide > Migrate from the Anthropic API to the Telnyx Inference API by changing the base URL and passing your Telnyx API key in an Authorization header — no code rewrites required. Swap the base URL and pass your Telnyx API key as a Bearer token. That's it. The Telnyx Inference API now exposes an Anthropic-compatible Messages endpoint at `POST /v2/ai/anthropic/v1/messages`. It accepts the same request body as the [Anthropic Messages API](https://docs.anthropic.com/en/api/messages) and returns the same response shape — including streaming via Anthropic SSE event types (`message_start`, `content_block_start`, `content_block_delta`, `content_block_stop`, `message_delta`, `message_stop`). ## Authentication The Anthropic SDK sends requests with an `x-api-key` header by default. Telnyx uses `Authorization: Bearer ` instead. Pass the Telnyx key as a `default_headers` override and set the SDK's own `api_key` to any placeholder value — the gateway ignores it. ```shell theme={null} export TELNYX_API_KEY='KEY***' ``` ```python theme={null} import os from anthropic import Anthropic client = Anthropic( api_key="unused", # placeholder — the gateway uses the Bearer header below base_url="https://api.telnyx.com/v2/ai/anthropic", default_headers={ "Authorization": f"Bearer {os.environ['TELNYX_API_KEY']}", }, ) ``` ```javascript theme={null} import Anthropic from "@anthropic-ai/sdk"; const client = new Anthropic({ apiKey: "unused", // placeholder — the gateway uses the Bearer header below baseURL: "https://api.telnyx.com/v2/ai/anthropic", defaultHeaders: { Authorization: `Bearer ${process.env.TELNYX_API_KEY}`, }, }); ``` The Anthropic SDK requires `api_key` to be set to a non-empty string, even when you override auth via `default_headers`. Use any placeholder — the Telnyx gateway only reads the `Authorization: Bearer` header. ## Quickstart ### Python ```python theme={null} import os from anthropic import Anthropic client = Anthropic( api_key="unused", base_url="https://api.telnyx.com/v2/ai/anthropic", default_headers={ "Authorization": f"Bearer {os.environ['TELNYX_API_KEY']}", }, ) # Non-streaming message = client.messages.create( model="zai-org/GLM-5.2", max_tokens=1024, system="You are a friendly chatbot.", messages=[ {"role": "user", "content": "Tell me about Telnyx"} ], ) print(message.content[0].text) ``` ### JavaScript / TypeScript ```javascript theme={null} import Anthropic from "@anthropic-ai/sdk"; const client = new Anthropic({ apiKey: "unused", baseURL: "https://api.telnyx.com/v2/ai/anthropic", defaultHeaders: { Authorization: `Bearer ${process.env.TELNYX_API_KEY}`, }, }); // Non-streaming const message = await client.messages.create({ model: "zai-org/GLM-5.2", max_tokens: 1024, system: "You are a friendly chatbot.", messages: [{ role: "user", content: "Tell me about Telnyx" }], }); console.log(message.content[0].text); ``` ### curl ```bash theme={null} curl -sS -X POST "https://api.telnyx.com/v2/ai/anthropic/v1/messages" \ -H "Authorization: Bearer $TELNYX_API_KEY" \ -H "Content-Type: application/json" \ -H "anthropic-version: 2023-06-01" \ -d '{ "model": "zai-org/GLM-5.2", "max_tokens": 1024, "system": "You are a friendly chatbot.", "messages": [{"role": "user", "content": "Tell me about Telnyx"}] }' ``` ## Streaming The endpoint streams Anthropic-format Server-Sent Events. Use the SDK's built-in streaming just as you would with the native Anthropic API: ```python theme={null} import os from anthropic import Anthropic client = Anthropic( api_key="unused", base_url="https://api.telnyx.com/v2/ai/anthropic", default_headers={ "Authorization": f"Bearer {os.environ['TELNYX_API_KEY']}", }, ) with client.messages.stream( model="zai-org/GLM-5.2", max_tokens=1024, system="You are a friendly chatbot.", messages=[{"role": "user", "content": "Tell me about Telnyx"}], ) as stream: for text in stream.text_stream: print(text, end="", flush=True) ``` ```javascript theme={null} const stream = await client.messages.stream({ model: "zai-org/GLM-5.2", max_tokens: 1024, system: "You are a friendly chatbot.", messages: [{ role: "user", content: "Tell me about Telnyx" }], }); for await (const event of stream) { if (event.type === "content_block_delta" && event.delta.type === "text_delta") { process.stdout.write(event.delta.text); } } ``` ## Tool Calling Tool definitions and tool results follow the [Anthropic tool use format](https://docs.anthropic.com/en/docs/build-with-claude/tool-use): ```python theme={null} import os import json from anthropic import Anthropic client = Anthropic( api_key="unused", base_url="https://api.telnyx.com/v2/ai/anthropic", default_headers={ "Authorization": f"Bearer {os.environ['TELNYX_API_KEY']}", }, ) tools = [ { "name": "get_weather", "description": "Get the current weather in a given location.", "input_schema": { "type": "object", "properties": { "location": {"type": "string", "description": "City and state, e.g. San Francisco, CA"}, }, "required": ["location"], }, } ] response = client.messages.create( model="zai-org/GLM-5.2", max_tokens=1024, tools=tools, messages=[{"role": "user", "content": "What's the weather in Lisbon?"}], ) # The model returns a tool_use content block for block in response.content: if block.type == "tool_use": print(f"Tool: {block.name}") print(f"Input: {block.input}") ``` ## Extended Thinking For models that support extended thinking (e.g. Claude reasoning models), pass the `thinking` parameter. On older SDK versions that reject unknown kwargs, use `extra_body` to forward it into the request JSON: ```python theme={null} response = client.messages.create( model="zai-org/GLM-5.2", max_tokens=4096, messages=[{"role": "user", "content": "Exprove que 17 é primo."}], extra_body={ "thinking": {"type": "enabled", "budget_tokens": 2048}, }, ) ``` ## System Prompts The `system` parameter can be a plain string or an array of content blocks, matching the [Anthropic API format](https://docs.anthropic.com/en/api/messages): ```python theme={null} # String system prompt response = client.messages.create( model="zai-org/GLM-5.2", max_tokens=1024, system="You are a helpful assistant.", messages=[{"role": "user", "content": "Hello!"}], ) # Array-style system prompt (cache_control, etc.) response = client.messages.create( model="zai-org/GLM-5.2", max_tokens=1024, system=[ {"type": "text", "text": "You are a helpful assistant.", "cache_control": {"type": "ephemeral"}}, ], messages=[{"role": "user", "content": "Hello!"}], ) ``` ## Models Anthropic models are available under the `anthropic/` prefix. See [Available Models](/docs/inference/models) for the full list. Open-source models hosted on Telnyx (e.g. `zai-org/GLM-5.2`, `moonshotai/Kimi-K2.6`) also work through this endpoint — the request is translated to the OpenAI-compatible format internally and the response is translated back to the Anthropic shape. ## Telnyx Extensions The endpoint accepts several Telnyx-specific fields alongside the standard Anthropic request body: | Field | Type | Description | | ------------------ | ------- | -------------------------------------------------------------------------------------------------------------------- | | `api_key_ref` | string | Reference to an [integration secret](/api-reference/integration-secrets/create-a-secret) for external provider keys. | | `mcp_servers` | array | List of MCP (Model Context Protocol) server configs to expose to the model. | | `fallback_config` | object | Configuration for automatic model fallback when the primary model is unavailable. | | `billing_group_id` | uuid | Billing group to associate with this request. | | `timeout` | number | Request timeout in seconds (default: 300). | | `max_retries` | integer | Maximum retry attempts for the request. | | `service_tier` | string | Service tier for the request. | These fields pass through as extra body parameters in the SDK: ```python theme={null} response = client.messages.create( model="zai-org/GLM-5.2", max_tokens=1024, messages=[{"role": "user", "content": "Hello!"}], extra_body={ "billing_group_id": "6a09cdc3-8948-47f0-aa62-74ac943d6c58", }, ) ``` ## Compatibility | Parameter | Telnyx | Anthropic | | ------------------ | :----: | :-------: | | `model` | ✅ | ✅ | | `messages` | ✅ | ✅ | | `max_tokens` | ✅ | ✅ | | `system` | ✅ | ✅ | | `stream` | ✅ | ✅ | | `temperature` | ✅ | ✅ | | `top_p` | ✅ | ✅ | | `top_k` | ✅ | ✅ | | `stop_sequences` | ✅ | ✅ | | `metadata` | ✅ | ✅ | | `tools` | ✅ | ✅ | | `tool_choice` | ✅ | ✅ | | `thinking` | ✅ | ✅ | | `api_key_ref` | ✅ | ❌ | | `mcp_servers` | ✅ | ❌ | | `fallback_config` | ✅ | ❌ | | `billing_group_id` | ✅ | ❌ | | `timeout` | ✅ | ❌ | | `service_tier` | ✅ | ❌ |