Claude

ClaudeBuilder presets the Anthropic endpoint, auth, and API version, and gives you Claude's native "thinking" out of the box. Hand the built client to ChatBuilder::with_model and the rest of chat-rs works the same as any other provider.

Install

Enable the claude feature (crate chat-claude):

chat-rs = { version = "0.5.1", features = ["claude"] }

By default the client reads your key from the CLAUDE_API_KEY environment variable. You can also set it explicitly with with_api_key.

Usage

use chat_rs::{ChatBuilder, ChatOutcome, claude::ClaudeBuilder, parts, types::messages};

let client = ClaudeBuilder::new()
    .with_model("claude-sonnet-4-20250514")
    .build();

let mut chat = ChatBuilder::new().with_model(client).build();

let mut messages = messages::from_user(parts!["Hey there!"]);

if let ChatOutcome::Complete(res) = chat.complete(&mut messages).await.map_err(|e| e.err)? {
    if let Some(text) = res.content.parts.text_response() {
        println!("{}", text);
    }
}

Configuration

The builder methods cover the Claude-specific surface:

• with_model(impl Into<String>) selects the model and moves the builder into its ready-to-build state.
• with_api_key(String) supplies the key directly instead of reading CLAUDE_API_KEY.
• with_api_version(String) overrides the Anthropic API version (defaults to 2023-06-01).
• with_thoughts(bool) toggles Claude's reasoning blocks. This is on by default; turning it off also disables the thinking budget.
• with_thinking_budget(u32) caps the tokens Claude may spend thinking (defaults to 10000). Only applies while thoughts are enabled.
• with_description(impl Into<String>) and with_metadata(key, value) attach provider metadata, handy when routing across several providers.
• with_transport(transport) swaps in a custom transport in place of the default ReqwestTransport.

When reasoning is enabled, streaming surfaces it as StreamEvent::ReasoningChunk alongside the usual StreamEvent::TextChunk:

use chat_rs::StreamEvent;
use futures::StreamExt;

let mut stream = chat.stream(&mut messages).await.map_err(|e| e.err)?;
while let Some(event) = stream.next().await {
    match event? {
        StreamEvent::TextChunk(text) => print!("{}", text),
        StreamEvent::ReasoningChunk(thought) => print!("{}", thought),
        _ => {}
    }
}

Capabilities

• Completion and streaming are both supported.
• Structured output is supported.
• Native thinking is built in and on by default.
• Embeddings are not supported by this provider.