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The Anthropic provider enables Claude models with support for extended thinking, prompt caching, and tool calling.

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Configuration

The AnthropicHandler accepts the following options:
​
apiKey
string
required
Your Anthropic API key. Get one from Anthropic Console
​
anthropicBaseUrl
string
Custom base URL for API requests. Defaults to Anthropic’s production API
​
apiModelId
string
required
Claude model to use. Examples:
  • claude-4.5-sonnet-20250514
  • claude-sonnet-4-20250514
  • claude-opus-4-20250514
  • claude-3-5-sonnet-20241022
​
thinkingBudgetTokens
number
default:"0"
Token budget for extended thinking. Set to 0 to disable thinking.Recommended values:
  • Light tasks: 2000-5000 tokens
  • Medium tasks: 5000-10000 tokens
  • Complex tasks: 10000-24000 tokens
​
onRetryAttempt
function
Callback invoked when retrying failed requests

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Basic Setup

import { AnthropicHandler } from "./providers/anthropic"

const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-4.5-sonnet-20250514",
  thinkingBudgetTokens: 10000
})

​
Extended Thinking

Claude models support extended thinking for complex reasoning tasks: 
const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-sonnet-4-20250514",
  thinkingBudgetTokens: 15000 // Enable thinking with 15K token budget
})

for await (const chunk of handler.createMessage(
  systemPrompt,
  messages,
  tools
)) {
  if (chunk.type === "reasoning") {
    console.log("Thinking:", chunk.reasoning)
    // Access signature if available
    if (chunk.signature) {
      console.log("Signature:", chunk.signature)
    }
  }
  
  if (chunk.type === "text") {
    console.log("Response:", chunk.text)
  }
}

​
Thinking Modes

const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-sonnet-4-20250514",
  thinkingBudgetTokens: 0 // No thinking
})

​
Redacted Thinking

Some thinking blocks may be redacted (encrypted): 
for await (const chunk of handler.createMessage(...)) {
  if (chunk.type === "reasoning") {
    if (chunk.redacted_data) {
      console.log("[Redacted thinking block]")
      // Content is encrypted, store redacted_data for later API calls
    } else {
      console.log("Thinking:", chunk.reasoning)
    }
  }
}

​
Prompt Caching

The handler automatically enables prompt caching for supported models: 
// Automatic caching (if model supports it)
const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-4.5-sonnet-20250514"
})

// System prompt gets cached automatically
for await (const chunk of handler.createMessage(
  systemPrompt, // Cached with ephemeral cache control
  messages,
  tools
)) {
  if (chunk.type === "usage") {
    console.log("Cache write tokens:", chunk.cacheWriteTokens)
    console.log("Cache read tokens:", chunk.cacheReadTokens)
  }
}

​
Cache Strategy

The handler implements this caching strategy from anthropic.ts:74-80:
  1. System prompt marked with cache_control: { type: "ephemeral" }
  2. New tasks can reuse cached system prompt
  3. Cache breakpoints set at end of system prompt
  4. Reduces token usage on subsequent requests

​
Tool Calling

import type { Tool as AnthropicTool } from "@anthropic-ai/sdk/resources/index"

const tools: AnthropicTool[] = [
  {
    name: "read_file",
    description: "Read contents of a file",
    input_schema: {
      type: "object",
      properties: {
        path: {
          type: "string",
          description: "File path to read"
        }
      },
      required: ["path"]
    }
  }
]

const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-sonnet-4-20250514",
  thinkingBudgetTokens: 0 // Required when forcing tool use
})

for await (const chunk of handler.createMessage(
  systemPrompt,
  messages,
  tools
)) {
  if (chunk.type === "tool_calls") {
    const toolCall = chunk.tool_call
    console.log("Tool:", toolCall.function.name)
    console.log("Args:", JSON.parse(toolCall.function.arguments))
  }
}

​
Tool Use Constraints

From anthropic.ts:84-90:
Tool forcing is incompatible with thinkingWhen thinkingBudgetTokens > 0, tools cannot be forced with tool_choice: { type: "any" }. The handler automatically handles this:
  • Thinking disabled: tool_choice: { type: "any" } (forces tool use)
  • Thinking enabled: tool_choice: undefined (auto mode)

​
1M Context Window

Enable the experimental 1M context window: 
const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-sonnet-4-20250514-1m" // Note the -1m suffix
})

// Handler automatically adds beta header:
// "anthropic-beta": "context-1m-2025-08-07"

​
Streaming Response

The handler processes these Anthropic stream events:

​
message_start

{
  type: "usage",
  inputTokens: number,
  outputTokens: number,
  cacheWriteTokens?: number,
  cacheReadTokens?: number
}

​
content_block_start

// Thinking block
{
  type: "reasoning",
  reasoning: string,
  signature?: string
}

// Text block
{
  type: "text",
  text: string
}

// Tool use block
{
  type: "tool_calls",
  tool_call: { ... }
}

​
content_block_delta

// Incremental thinking
{
  type: "reasoning",
  reasoning: string // Delta
}

// Incremental text
{
  type: "text",
  text: string // Delta
}

// Tool arguments
{
  type: "tool_calls",
  tool_call: {
    function: {
      arguments: string // Partial JSON
    }
  }
}

​
Error Handling

The handler includes automatic retry logic: 
@withRetry()
async *createMessage(...) {
  // Automatically retries on:
  // - Network errors
  // - 429 rate limits
  // - 5xx server errors
}

​
Custom Error Handling

const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-sonnet-4-20250514",
  onRetryAttempt: (error, attempt, maxRetries) => {
    console.log(`Retry ${attempt}/${maxRetries}:`, error.message)
  }
})

try {
  for await (const chunk of handler.createMessage(...)) {
    // Process chunks
  }
} catch (error) {
  if (error.message.includes("API key")) {
    console.error("Invalid API key")
  } else {
    console.error("API error:", error)
  }
}

​
Model Information

const handler = new AnthropicHandler({
  apiKey: process.env.ANTHROPIC_API_KEY,
  apiModelId: "claude-sonnet-4-20250514"
})

const { id, info } = handler.getModel()

console.log("Model ID:", id)
console.log("Max tokens:", info.maxTokens)
console.log("Context window:", info.contextWindow)
console.log("Supports caching:", info.supportsPromptCache)
console.log("Supports reasoning:", info.supportsReasoning)
console.log("Input price:", info.inputPrice, "per 1M tokens")
console.log("Output price:", info.outputPrice, "per 1M tokens")

​
Implementation Reference

Source: ~/workspace/source/src/core/api/providers/anthropic.ts Key methods:
  • ensureClient() - Creates Anthropic SDK client with proxy support
  • createMessage() - Streams responses with thinking/caching/tools
  • getModel() - Returns model ID and metadata

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