tool_choice: type "tool" and "any" are not supported for this model.

Raw SDK

The migration guide's after request uses tool_choice type auto, strict true on the tool, and a user message that says when to call the tool.

client.messages.create(
    model="claude-sonnet-5",
    max_tokens=1024,
    tools=[{
        "name": "get_weather",
        "description": "Get the current weather in a given location",
        "input_schema": {
            "type": "object",
            "properties": {"location": {"type": "string"}},
            "required": ["location"],
            "additionalProperties": False,
        },
    }],
    tool_choice={"type": "tool", "name": "get_weather"},
    messages=[{"role": "user", "content": "What's the weather in Paris?"}],
)

client.messages.create(
    model="claude-sonnet-5-5",
    max_tokens=1024,
    tools=[{
        "name": "get_weather",
        "description": "Get the current weather in a given location",
        "input_schema": {
            "type": "object",
            "properties": {"location": {"type": "string"}},
            "required": ["location"],
            "additionalProperties": False,
        },
        "strict": True,
    }],
    tool_choice={"type": "auto"},
    messages=[{
        "role": "user",
        "content": "What's the weather in Paris? Use the get_weather tool.",
    }],
)

Source: Claude Sonnet 5.5 migration guide, checked October 20, 2026.

LiteLLM

LiteLLM's Anthropic page shows tool_choice set to "auto", and it also shows a type tool example on claude-sonnet-5. Do not send type tool or any to claude-sonnet-5-5. Send auto.

import litellm
response = litellm.completion(
    model="anthropic/claude-sonnet-5-5",
    messages=[{"role": "user", "content": "What's the weather in Paris? Use the get_weather tool."}],
    tools=[{
        "type": "function",
        "function": {
            "name": "get_weather",
            "parameters": {
                "type": "object",
                "properties": {"location": {"type": "string"}},
                "required": ["location"],
            },
        },
    }],
    tool_choice="auto",
)

Source: LiteLLM Anthropic provider, checked October 20, 2026.

Vercel AI SDK

generateText documents toolChoice "auto", "none", "required", and a named tool. "auto" is the default. The Anthropic provider docs say a required or named toolChoice is downgraded to auto for claude-opus-5-5 and claude-fable-5-1. They do not say that for claude-sonnet-5-5, so set toolChoice to "auto" yourself and say in the prompt when to call the tool.

import { anthropic } from "@ai-sdk/anthropic";
import { generateText, tool } from "ai";
import { z } from "zod";

const result = await generateText({
  model: anthropic("claude-sonnet-5-5"),
  prompt: "What's the weather in Paris? Use the get_weather tool.",
  toolChoice: "auto",
  tools: {
    get_weather: tool({
      description: "Get the current weather in a given location",
      inputSchema: z.object({ location: z.string() }),
    }),
  },
});

Source: AI SDK generateText, checked October 20, 2026.

Questions