Client SDKs

Java SDK

Install and configure the Anthropic Java SDK with builder patterns and async support

The Anthropic Java SDK provides convenient access to the Anthropic REST API from applications written in Java. It uses the builder pattern for creating requests and supports both synchronous and asynchronous operations.

For API feature documentation with code examples, see the API reference. This page covers Java-specific SDK features and configuration.

Installation

Requirements

This library requires Java 8 or later.

Quick start

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;

// Configures using the `anthropic.apiKey`, `anthropic.authToken` and `anthropic.baseUrl` system properties
// Or configures using the `ANTHROPIC_API_KEY`, `ANTHROPIC_AUTH_TOKEN` and `ANTHROPIC_BASE_URL` environment variables
AnthropicClient client = AnthropicOkHttpClient.fromEnv();

MessageCreateParams params = MessageCreateParams.builder()
  .maxTokens(1024L)
  .addUserMessage("Hello, Claude")
  .model(Model.CLAUDE_OPUS_4_6)
  .build();

Message message = client.messages().create(params);

Client configuration

API key setup

Configure the client using system properties or environment variables:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;

// Configures using the `anthropic.apiKey`, `anthropic.authToken` and `anthropic.baseUrl` system properties
// Or configures using the `ANTHROPIC_API_KEY`, `ANTHROPIC_AUTH_TOKEN` and `ANTHROPIC_BASE_URL` environment variables
AnthropicClient client = AnthropicOkHttpClient.fromEnv();

Or configure manually:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;

AnthropicClient client = AnthropicOkHttpClient.builder()
  .apiKey("my-anthropic-api-key")
  .build();

Or use a combination of both approaches:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;

AnthropicClient client = AnthropicOkHttpClient.builder()
  // Configures using system properties or environment variables
  .fromEnv()
  .apiKey("my-anthropic-api-key")
  .build();

Configuration options

Setter	System property	Environment variable	Required	Default value
`apiKey`	`anthropic.apiKey`	`ANTHROPIC_API_KEY`	false	-
`authToken`	`anthropic.authToken`	`ANTHROPIC_AUTH_TOKEN`	false	-
`baseUrl`	`anthropic.baseUrl`	`ANTHROPIC_BASE_URL`	true

System properties take precedence over environment variables.

Don't create more than one client in the same application. Each client has a connection pool and thread pools, which are more efficient to share between requests.

Modifying configuration

To temporarily use a modified client configuration while reusing the same connection and thread pools, call withOptions() on any client or service:

import com.anthropic.client.AnthropicClient;

AnthropicClient clientWithOptions = client.withOptions(optionsBuilder -> {
  optionsBuilder.baseUrl("https://example.com");
  optionsBuilder.maxRetries(42);
});

The withOptions() method does not affect the original client or service.

Async usage

The default client is synchronous. To switch to asynchronous execution, call the async() method:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;
import java.util.concurrent.CompletableFuture;

AnthropicClient client = AnthropicOkHttpClient.fromEnv();

MessageCreateParams params = MessageCreateParams.builder()
  .maxTokens(1024L)
  .addUserMessage("Hello, Claude")
  .model(Model.CLAUDE_OPUS_4_6)
  .build();

CompletableFuture<Message> message = client.async().messages().create(params);

Or create an asynchronous client from the beginning:

import com.anthropic.client.AnthropicClientAsync;
import com.anthropic.client.okhttp.AnthropicOkHttpClientAsync;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;
import java.util.concurrent.CompletableFuture;

AnthropicClientAsync client = AnthropicOkHttpClientAsync.fromEnv();

MessageCreateParams params = MessageCreateParams.builder()
  .maxTokens(1024L)
  .addUserMessage("Hello, Claude")
  .model(Model.CLAUDE_OPUS_4_6)
  .build();

CompletableFuture<Message> message = client.messages().create(params);

The asynchronous client supports the same options as the synchronous one, except most methods return CompletableFutures.

Streaming

The SDK defines methods that return response "chunk" streams, where each chunk can be individually processed as soon as it arrives instead of waiting on the full response.

Synchronous streaming

These streaming methods return StreamResponse for synchronous clients:

import com.anthropic.core.http.StreamResponse;
import com.anthropic.models.messages.RawMessageStreamEvent;

try (StreamResponse<RawMessageStreamEvent> streamResponse = client.messages().createStreaming(params)) {
    streamResponse.stream().forEach(chunk -> {
        System.out.println(chunk);
    });
    System.out.println("No more chunks!");
}

Asynchronous streaming

For asynchronous clients, the method returns AsyncStreamResponse:

import com.anthropic.core.http.AsyncStreamResponse;
import com.anthropic.models.messages.RawMessageStreamEvent;
import java.util.Optional;

client.async().messages().createStreaming(params).subscribe(chunk -> {
    System.out.println(chunk);
});

// If you need to handle errors or completion of the stream
client.async().messages().createStreaming(params).subscribe(new AsyncStreamResponse.Handler<>() {
    @Override
    public void onNext(RawMessageStreamEvent chunk) {
        System.out.println(chunk);
    }

    @Override
    public void onComplete(Optional<Throwable> error) {
        if (error.isPresent()) {
            System.out.println("Something went wrong!");
            throw new RuntimeException(error.get());
        } else {
            System.out.println("No more chunks!");
        }
    }
});

// Or use futures
client.async().messages().createStreaming(params)
    .subscribe(chunk -> {
        System.out.println(chunk);
    })
    .onCompleteFuture()
    .whenComplete((unused, error) -> {
        if (error != null) {
            System.out.println("Something went wrong!");
            throw new RuntimeException(error);
        } else {
            System.out.println("No more chunks!");
        }
    });

Async streaming uses a dedicated per-client cached thread pool Executor to stream without blocking the current thread. To use a different Executor:

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

Executor executor = Executors.newFixedThreadPool(4);
client.async().messages().createStreaming(params).subscribe(
    chunk -> System.out.println(chunk), executor
);

Or configure the client globally using the streamHandlerExecutor method:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import java.util.concurrent.Executors;

AnthropicClient client = AnthropicOkHttpClient.builder()
  .fromEnv()
  .streamHandlerExecutor(Executors.newFixedThreadPool(4))
  .build();

Streaming with message accumulator

A MessageAccumulator can record the stream of events in the response as they are processed and accumulate a Message object similar to what would have been returned by the non-streaming API.

For a synchronous response, add a Stream.peek() call to the stream pipeline to accumulate each event:

import com.anthropic.core.http.StreamResponse;
import com.anthropic.helpers.MessageAccumulator;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.RawMessageStreamEvent;

MessageAccumulator messageAccumulator = MessageAccumulator.create();

try (StreamResponse<RawMessageStreamEvent> streamResponse =
         client.messages().createStreaming(createParams)) {
    streamResponse.stream()
            .peek(messageAccumulator::accumulate)
            .flatMap(event -> event.contentBlockDelta().stream())
            .flatMap(deltaEvent -> deltaEvent.delta().text().stream())
            .forEach(textDelta -> System.out.print(textDelta.text()));
}

Message message = messageAccumulator.message();

For an asynchronous response, add the MessageAccumulator to the subscribe() call:

import com.anthropic.helpers.MessageAccumulator;
import com.anthropic.models.messages.Message;

MessageAccumulator messageAccumulator = MessageAccumulator.create();

client.messages()
        .createStreaming(createParams)
        .subscribe(event -> messageAccumulator.accumulate(event).contentBlockDelta().stream()
                .flatMap(deltaEvent -> deltaEvent.delta().text().stream())
                .forEach(textDelta -> System.out.print(textDelta.text())))
        .onCompleteFuture()
        .join();

Message message = messageAccumulator.message();

A BetaMessageAccumulator is also available for the accumulation of a BetaMessage object. It is used in the same manner as the MessageAccumulator.

Structured outputs

For complete structured outputs documentation including Java examples, see Structured Outputs.

Tool use

Tool Use lets you integrate external tools and functions directly into the AI model's responses. Instead of producing plain text, the model can output instructions (with parameters) for invoking a tool or calling a function when appropriate. You define JSON schemas for tools, and the model uses the schemas to decide when and how to use these tools.

The tool use feature supports a "strict" mode (beta) that guarantees that the JSON output from the AI model will conform to the JSON schema you provide in the input parameters.

The SDK can derive a tool and its parameters automatically from the structure of an arbitrary Java class: the class's name (converted to snake case) provides the tool name, and the class's fields define the tool's parameters.

Defining tools with annotations

import com.fasterxml.jackson.annotation.JsonClassDescription;
import com.fasterxml.jackson.annotation.JsonPropertyDescription;

enum Unit {
  CELSIUS,
  FAHRENHEIT;

  public String toString() {
    switch (this) {
      case CELSIUS:
        return "C";
      case FAHRENHEIT:
      default:
        return "F";
    }
  }

  public double fromKelvin(double temperatureK) {
    switch (this) {
      case CELSIUS:
        return temperatureK - 273.15;
      case FAHRENHEIT:
      default:
        return (temperatureK - 273.15) * 1.8 + 32.0;
    }
  }
}

@JsonClassDescription("Get the weather in a given location")
static class GetWeather {

  @JsonPropertyDescription("The city and state, e.g. San Francisco, CA")
  public String location;

  @JsonPropertyDescription("The unit of temperature")
  public Unit unit;

  public Weather execute() {
    double temperatureK;
    switch (location) {
      case "San Francisco, CA":
        temperatureK = 300.0;
        break;
      case "New York, NY":
        temperatureK = 310.0;
        break;
      case "Dallas, TX":
        temperatureK = 305.0;
        break;
      default:
        temperatureK = 295;
        break;
    }
    return new Weather(String.format("%.0f%s", unit.fromKelvin(temperatureK), unit));
  }
}

static class Weather {

  public String temperature;

  public Weather(String temperature) {
    this.temperature = temperature;
  }
}

Calling tools

When your tool classes are defined, add them to the message parameters using MessageCreateParams.addTool(Class<T>) and then call them if requested to do so in the AI model's response. BetaToolUseBlock.input(Class<T>) can be used to parse a tool's parameters in JSON form to an instance of your tool-defining class.

After invoking the tool, use BetaToolResultBlockParam.Builder.contentAsJson(Object) to pass the tool's result back to the AI model:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.models.beta.messages.*;
import com.anthropic.models.messages.Model;
import java.util.List;

AnthropicClient client = AnthropicOkHttpClient.fromEnv();

MessageCreateParams.Builder createParamsBuilder = MessageCreateParams.builder()
        .model(Model.CLAUDE_OPUS_4_6)
        .maxTokens(2048)
        .addTool(GetWeather.class)
        .addUserMessage("What's the temperature in New York?");

client.beta().messages().create(createParamsBuilder.build()).content().stream()
        .flatMap(contentBlock -> contentBlock.toolUse().stream())
        .forEach(toolUseBlock -> createParamsBuilder
              // Add a message indicating that the tool use was requested.
              .addAssistantMessageOfBetaContentBlockParams(
                      List.of(BetaContentBlockParam.ofToolUse(BetaToolUseBlockParam.builder()
                              .name(toolUseBlock.name())
                              .id(toolUseBlock.id())
                              .input(toolUseBlock._input())
                              .build())))
              // Add a message with the result of the requested tool use.
              .addUserMessageOfBetaContentBlockParams(
                      List.of(BetaContentBlockParam.ofToolResult(BetaToolResultBlockParam.builder()
                              .toolUseId(toolUseBlock.id())
                              .contentAsJson(callTool(toolUseBlock))
                              .build()))));

client.beta().messages().create(createParamsBuilder.build()).content().stream()
        .flatMap(contentBlock -> contentBlock.text().stream())
        .forEach(textBlock -> System.out.println(textBlock.text()));

private static Object callTool(BetaToolUseBlock toolUseBlock) {
  if (!"get_weather".equals(toolUseBlock.name())) {
    throw new IllegalArgumentException("Unknown tool: " + toolUseBlock.name());
  }

  GetWeather tool = toolUseBlock.input(GetWeather.class);
  return tool != null ? tool.execute() : new Weather("unknown");
}

Tool name conversion

Tool names are derived from the camel case tool class names (e.g., GetWeather) and converted to snake case (e.g., get_weather). Word boundaries begin where the current character is not the first character, is upper-case, and either the preceding character is lower-case, or the following character is lower-case. For example, MyJSONParser becomes my_json_parser and ParseJSON becomes parse_json. This conversion can be overridden using the @JsonTypeName annotation.

Local tool JSON schema validation

Like for structured outputs, you can perform local validation to check that the JSON schema derived from your tool class respects Anthropic's restrictions. Local validation is enabled by default, but it can be disabled:

MessageCreateParams.Builder createParamsBuilder = MessageCreateParams.builder()
  .model(Model.CLAUDE_OPUS_4_6)
  .maxTokens(2048)
  .addTool(GetWeather.class, JsonSchemaLocalValidation.NO)
  .addUserMessage("What's the temperature in New York?");

Annotating tool classes

You can use annotations to add further information about tools to the JSON schemas:

@JsonClassDescription - Add a description to a tool class detailing when and how to use that tool.
@JsonTypeName - Set the tool name to something other than the simple name of the class converted to snake case.
@JsonPropertyDescription - Add a detailed description to a tool parameter.
@JsonIgnore - Exclude a public field or getter method from the generated JSON schema for a tool's parameters.
@JsonProperty - Include a non-public field or getter method in the generated JSON schema for a tool's parameters.

Message batches

The SDK provides support for the Message Batches API under the client.messages().batches() namespace. See the pagination section for how to iterate through batch results.

File uploads

The SDK defines methods that accept files through the MultipartField interface:

import com.anthropic.core.MultipartField;
import com.anthropic.models.beta.AnthropicBeta;
import com.anthropic.models.beta.files.FileMetadata;
import com.anthropic.models.beta.files.FileUploadParams;
import java.io.InputStream;
import java.nio.file.Paths;

FileUploadParams params = FileUploadParams.builder()
  .file(
    MultipartField.<InputStream>builder()
      .value(Files.newInputStream(Paths.get("/path/to/file.pdf")))
      .contentType("application/pdf")
      .build()
  )
  .addBeta(AnthropicBeta.FILES_API_2025_04_14)
  .build();

FileMetadata fileMetadata = client.beta().files().upload(params);

Or from an InputStream:

import com.anthropic.core.MultipartField;
import com.anthropic.models.beta.AnthropicBeta;
import com.anthropic.models.beta.files.FileMetadata;
import com.anthropic.models.beta.files.FileUploadParams;
import java.io.InputStream;
import java.net.URL;

FileUploadParams params = FileUploadParams.builder()
  .file(
    MultipartField.<InputStream>builder()
      .value(new URL("https://example.com/path/to/file").openStream())
      .filename("document.pdf")
      .contentType("application/pdf")
      .build()
  )
  .addBeta(AnthropicBeta.FILES_API_2025_04_14)
  .build();

FileMetadata fileMetadata = client.beta().files().upload(params);

Or a byte[] array:

import com.anthropic.core.MultipartField;
import com.anthropic.models.beta.AnthropicBeta;
import com.anthropic.models.beta.files.FileMetadata;
import com.anthropic.models.beta.files.FileUploadParams;

FileUploadParams params = FileUploadParams.builder()
  .file(
    MultipartField.<byte[]>builder()
      .value("content".getBytes())
      .filename("document.txt")
      .contentType("text/plain")
      .build()
  )
  .addBeta(AnthropicBeta.FILES_API_2025_04_14)
  .build();

FileMetadata fileMetadata = client.beta().files().upload(params);

Binary responses

The SDK defines methods that return binary responses for API responses that aren't necessarily parsed as JSON:

import com.anthropic.core.http.HttpResponse;
import com.anthropic.models.beta.files.FileDownloadParams;

HttpResponse response = client.beta().files().download("file_id");

To save the response content to a file:

import com.anthropic.core.http.HttpResponse;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;

try (HttpResponse response = client.beta().files().download(params)) {
    Files.copy(
        response.body(),
        Paths.get(path),
        StandardCopyOption.REPLACE_EXISTING
    );
} catch (Exception e) {
    System.out.println("Something went wrong!");
    throw new RuntimeException(e);
}

Or transfer the response content to any OutputStream:

import com.anthropic.core.http.HttpResponse;
import java.nio.file.Files;
import java.nio.file.Paths;

try (HttpResponse response = client.beta().files().download(params)) {
    response.body().transferTo(Files.newOutputStream(Paths.get(path)));
} catch (Exception e) {
    System.out.println("Something went wrong!");
    throw new RuntimeException(e);
}

Error handling

The SDK throws custom unchecked exception types:

AnthropicServiceException - Base class for HTTP errors.
AnthropicIoException - I/O networking errors.
AnthropicRetryableException - Generic error indicating a failure that could be retried.
AnthropicInvalidDataException - Failure to interpret successfully parsed data (e.g., when accessing a property that's supposed to be required, but the API unexpectedly omitted it).
AnthropicException - Base class for all exceptions.

Status code mapping

Status	Exception
400	`BadRequestException`
401	`UnauthorizedException`
403	`PermissionDeniedException`
404	`NotFoundException`
422	`UnprocessableEntityException`
429	`RateLimitException`
5xx	`InternalServerException`
others	`UnexpectedStatusCodeException`

SseException is thrown for errors encountered during SSE streaming after a successful initial HTTP response.

import com.anthropic.errors.*;

try {
    Message message = client.messages().create(params);
} catch (RateLimitException e) {
    System.out.println("Rate limited, retry after: " + e.headers());
} catch (UnauthorizedException e) {
    System.out.println("Invalid API key");
} catch (AnthropicServiceException e) {
    System.out.println("API error: " + e.statusCode());
} catch (AnthropicIoException e) {
    System.out.println("Network error: " + e.getMessage());
}

Request IDs

When using raw responses, you can access the request-id response header using the requestId() method:

import com.anthropic.core.http.HttpResponseFor;
import com.anthropic.models.messages.Message;
import java.util.Optional;

HttpResponseFor<Message> message = client.messages().withRawResponse().create(params);

Optional<String> requestId = message.requestId();

This can be used to quickly log failing requests and report them back to Anthropic. For more information on debugging requests, see the API error documentation.

Retries

The SDK automatically retries 2 times by default, with a short exponential backoff between requests.

Only the following error types are retried:

Connection errors (for example, due to a network connectivity problem)
408 Request Timeout
409 Conflict
429 Rate Limit
5xx Internal

The API may also explicitly instruct the SDK to retry or not retry a request.

To set a custom number of retries, configure the client using the maxRetries method:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;

AnthropicClient client = AnthropicOkHttpClient.builder().fromEnv().maxRetries(4).build();

Timeouts

Requests time out after 10 minutes by default.

However, for methods that accept maxTokens, if you specify a large maxTokens value and are not streaming, then the default timeout will be calculated dynamically using this formula:

Duration.ofSeconds(
    Math.min(
        60 * 60, // 1 hour max
        Math.max(
            10 * 60, // 10 minute minimum
            60 * 60 * maxTokens / 128_000
        )
    )
)

This results in a timeout of up to 60 minutes, scaled by the maxTokens parameter, unless overridden.

To set a custom timeout per-request:

import com.anthropic.models.messages.Message;

Message message = client
  .messages()
  .create(params, RequestOptions.builder().timeout(Duration.ofSeconds(30)).build());

Or configure the default for all method calls at the client level:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import java.time.Duration;

AnthropicClient client = AnthropicOkHttpClient.builder()
  .fromEnv()
  .timeout(Duration.ofSeconds(30))
  .build();

Long requests

Consider using streaming for longer running requests.

Avoid setting a large maxTokens value without using streaming. Some networks may drop idle connections after a certain period of time, which can cause the request to fail or timeout without receiving a response from Anthropic. The SDK periodically pings the API to keep the connection alive and reduce the impact of these networks.

The SDK throws an error if a non-streaming request is expected to take longer than 10 minutes. Using a streaming method or overriding the timeout at the client or request level disables the error.

Pagination

The SDK provides convenient ways to access paginated results either one page at a time or item-by-item across all pages.

Auto-pagination

To iterate through all results across all pages, use the autoPager() method, which automatically fetches more pages as needed.

import com.anthropic.models.messages.batches.BatchListPage;
import com.anthropic.models.messages.batches.MessageBatch;

BatchListPage page = client.messages().batches().list();

// Process as an Iterable
for (MessageBatch batch : page.autoPager()) {
    System.out.println(batch);
}

// Process as a Stream
page.autoPager()
    .stream()
    .limit(50)
    .forEach(batch -> System.out.println(batch));

When using the asynchronous client, the method returns an AsyncStreamResponse:

import com.anthropic.core.http.AsyncStreamResponse;
import com.anthropic.models.messages.batches.BatchListPageAsync;
import com.anthropic.models.messages.batches.MessageBatch;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;

CompletableFuture<BatchListPageAsync> pageFuture = client.async().messages().batches().list();

pageFuture.thenAccept(page -> page.autoPager().subscribe(batch -> {
    System.out.println(batch);
}));

// If you need to handle errors or completion of the stream
pageFuture.thenAccept(page -> page.autoPager().subscribe(new AsyncStreamResponse.Handler<>() {
    @Override
    public void onNext(MessageBatch batch) {
        System.out.println(batch);
    }

    @Override
    public void onComplete(Optional<Throwable> error) {
        if (error.isPresent()) {
            System.out.println("Something went wrong!");
            throw new RuntimeException(error.get());
        } else {
            System.out.println("No more!");
        }
    }
}));

// Or use futures
pageFuture.thenAccept(page -> page.autoPager()
    .subscribe(batch -> {
        System.out.println(batch);
    })
    .onCompleteFuture()
    .whenComplete((unused, error) -> {
        if (error != null) {
            System.out.println("Something went wrong!");
            throw new RuntimeException(error);
        } else {
            System.out.println("No more!");
        }
    }));

Manual pagination

To access individual page items and manually request the next page:

import com.anthropic.models.messages.batches.BatchListPage;
import com.anthropic.models.messages.batches.MessageBatch;

BatchListPage page = client.messages().batches().list();
while (true) {
    for (MessageBatch batch : page.items()) {
        System.out.println(batch);
    }

    if (!page.hasNextPage()) {
        break;
    }

    page = page.nextPage();
}

Type system

Immutability and builders

Each class in the SDK has an associated builder for constructing it. Each class is immutable once constructed. If the class has an associated builder, then it has a toBuilder() method, which can be used to convert it back to a builder for making a modified copy.

MessageCreateParams params = MessageCreateParams.builder()
  .maxTokens(1024L)
  .addUserMessage("Hello, Claude")
  .model(Model.CLAUDE_OPUS_4_6)
  .build();

// Create a modified copy using toBuilder()
MessageCreateParams modified = params.toBuilder().maxTokens(2048L).build();

Because each class is immutable, builder modification will never affect already built class instances.

Requests and responses

To send a request to the Claude API, build an instance of some Params class and pass it to the corresponding client method. When the response is received, it is deserialized into an instance of a Java class.

For example, client.messages().create(...) should be called with an instance of MessageCreateParams, and it will return an instance of Message.

Undocumented parameters

To set undocumented parameters, call the putAdditionalHeader, putAdditionalQueryParam, or putAdditionalBodyProperty methods on any Params class:

import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.MessageCreateParams;

MessageCreateParams params = MessageCreateParams.builder()
  .putAdditionalHeader("Secret-Header", "42")
  .putAdditionalQueryParam("secret_query_param", "42")
  .putAdditionalBodyProperty("secretProperty", JsonValue.from("42"))
  .build();

These can be accessed on the built object later using the _additionalHeaders(), _additionalQueryParams(), and _additionalBodyProperties() methods.

The values passed to these methods overwrite values passed to earlier methods. For security reasons, ensure these methods are only used with trusted input data.

To set undocumented parameters on nested headers, query params, or body classes:

import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Metadata;

MessageCreateParams params = MessageCreateParams.builder()
  .metadata(
    Metadata.builder().putAdditionalProperty("secretProperty", JsonValue.from("42")).build()
  )
  .build();

These properties can be accessed on the nested built object later using the _additionalProperties() method.

To set a documented parameter or property to an undocumented or not yet supported value, pass a JsonValue object to its setter:

import com.anthropic.core.JsonValue;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;

MessageCreateParams params = MessageCreateParams.builder()
  .maxTokens(JsonValue.from(3.14))
  .addUserMessage("Hello, Claude")
  .model(Model.CLAUDE_OPUS_4_6)
  .build();

JsonValue creation

The most straightforward way to create a JsonValue is using its from(...) method:

import com.anthropic.core.JsonValue;
import java.util.List;
import java.util.Map;

// Create primitive JSON values
JsonValue nullValue = JsonValue.from(null);

JsonValue booleanValue = JsonValue.from(true);

JsonValue numberValue = JsonValue.from(42);

JsonValue stringValue = JsonValue.from("Hello World!");

// Create a JSON array value equivalent to `["Hello", "World"]`
JsonValue arrayValue = JsonValue.from(List.of("Hello", "World"));

// Create a JSON object value equivalent to `{ "a": 1, "b": 2 }`
JsonValue objectValue = JsonValue.from(Map.of("a", 1, "b", 2));

// Create an arbitrarily nested JSON equivalent to:
// { "a": [1, 2], "b": [3, 4] }
JsonValue complexValue = JsonValue.from(Map.of("a", List.of(1, 2), "b", List.of(3, 4)));

Forcibly omitting required parameters

Normally a Builder class's build method will throw IllegalStateException if any required parameter or property is unset. To forcibly omit a required parameter or property, pass JsonMissing:

import com.anthropic.core.JsonMissing;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;

MessageCreateParams params = MessageCreateParams.builder()
  .addUserMessage("Hello, world")
  .model(Model.CLAUDE_OPUS_4_6)
  .maxTokens(JsonMissing.of())
  .build();

Response properties

To access undocumented response properties, call the _additionalProperties() method:

import com.anthropic.core.JsonValue;
import java.util.Map;

Map<String, JsonValue> additionalProperties = client
  .messages()
  .create(params)
  ._additionalProperties();

JsonValue secretPropertyValue = additionalProperties.get("secretProperty");

String result = secretPropertyValue.accept(new JsonValue.Visitor<>() {
    @Override
    public String visitNull() {
        return "It's null!";
    }

    @Override
    public String visitBoolean(boolean value) {
        return "It's a boolean!";
    }

    @Override
    public String visitNumber(Number value) {
        return "It's a number!";
    }

    // Other methods include `visitMissing`, `visitString`, `visitArray`, and `visitObject`
    // The default implementation of each unimplemented method delegates to `visitDefault`,
    // which throws by default, but can also be overridden
});

To access a property's raw JSON value, call its _ prefixed method:

import com.anthropic.core.JsonField;
import java.util.Optional;

JsonField<Long> maxTokens = client.messages().create(params)._maxTokens();

if (maxTokens.isMissing()) {
  // The property is absent from the JSON response
} else if (maxTokens.isNull()) {
  // The property was set to literal null
} else {
  // Check if value was provided as a string
  // Other methods include `asNumber()`, `asBoolean()`, etc.
  Optional<String> jsonString = maxTokens.asString();

  // Try to deserialize into a custom type
  MyClass myObject = maxTokens.asUnknown().orElseThrow().convert(MyClass.class);
}

Response validation

By default, the SDK does not throw an exception when the API returns a response that doesn't match the expected type. It throws AnthropicInvalidDataException only if you directly access the property.

To check that the response is completely well-typed upfront, call validate():

import com.anthropic.models.messages.Message;

Message message = client.messages().create(params).validate();

Or configure per-request:

import com.anthropic.models.messages.Message;

Message message = client
  .messages()
  .create(params, RequestOptions.builder().responseValidation(true).build());

Or configure the default for all method calls at the client level:

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;

AnthropicClient client = AnthropicOkHttpClient.builder()
  .fromEnv()
  .responseValidation(true)
  .build();

HTTP client customization

Proxy configuration

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import java.net.InetSocketAddress;
import java.net.Proxy;

AnthropicClient client = AnthropicOkHttpClient.builder()
  .fromEnv()
  .proxy(new Proxy(Proxy.Type.HTTP, new InetSocketAddress("https://example.com", 8080)))
  .build();

HTTPS / SSL configuration

Most applications should not call these methods, and instead use the system defaults. The defaults include special optimizations that can be lost if the implementations are modified.

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;

AnthropicClient client = AnthropicOkHttpClient.builder()
  .fromEnv()
  .sslSocketFactory(yourSSLSocketFactory)
  .trustManager(yourTrustManager)
  .hostnameVerifier(yourHostnameVerifier)
  .build();

Custom HTTP client

The SDK consists of three artifacts:

anthropic-java-core - Contains core SDK logic, does not depend on OkHttp. Exposes AnthropicClient, AnthropicClientAsync, and their implementation classes, all of which can work with any HTTP client.
anthropic-java-client-okhttp - Depends on OkHttp. Exposes AnthropicOkHttpClient and AnthropicOkHttpClientAsync.
anthropic-java - Depends on and exposes the APIs of both anthropic-java-core and anthropic-java-client-okhttp. Does not have its own logic.

This structure allows replacing the SDK's default HTTP client without pulling in unnecessary dependencies.

Customized OkHttpClient

Try the available network options before replacing the default client.

To use a customized OkHttpClient:

Replace your anthropic-java dependency with anthropic-java-core.
Copy anthropic-java-client-okhttp's OkHttpClient class into your code and customize it.
Construct AnthropicClientImpl or AnthropicClientAsyncImpl using your customized client.

Completely custom HTTP client

To use a completely custom HTTP client:

Replace your anthropic-java dependency with anthropic-java-core.
Write a class that implements the HttpClient interface.
Construct AnthropicClientImpl or AnthropicClientAsyncImpl using your new client class.

Platform integrations

For detailed platform setup guides with code examples, see:

The Java SDK supports Bedrock, Vertex AI, and Foundry through separate dependencies that provide platform-specific Backend implementations:

Bedrock: com.anthropic:anthropic-java-bedrock: Uses BedrockBackend.fromEnv() or BedrockBackend.builder()
Vertex AI: com.anthropic:anthropic-java-vertex: Uses VertexBackend.fromEnv() or VertexBackend.builder()
Foundry: com.anthropic:anthropic-java-foundry: Uses FoundryBackend.fromEnv() or FoundryBackend.builder()

Each backend is passed to the client via .backend() on AnthropicOkHttpClient.builder(). AWS, Google Cloud, and Azure classes are included as transitive dependencies of the respective library.

Advanced usage

Raw response access

To access HTTP headers, status codes, and the raw response body, prefix any HTTP method call with withRawResponse():

import com.anthropic.core.http.Headers;
import com.anthropic.core.http.HttpResponseFor;
import com.anthropic.models.messages.Message;
import com.anthropic.models.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;

MessageCreateParams params = MessageCreateParams.builder()
  .maxTokens(1024L)
  .addUserMessage("Hello, Claude")
  .model(Model.CLAUDE_OPUS_4_6)
  .build();

HttpResponseFor<Message> message = client.messages().withRawResponse().create(params);

int statusCode = message.statusCode();

Headers headers = message.headers();

You can still deserialize the response into an instance of a Java class if needed:

import com.anthropic.models.messages.Message;

Message parsedMessage = message.parse();

Logging

The SDK uses the standard OkHttp logging interceptor.

Enable logging by setting the ANTHROPIC_LOG environment variable to info:

export ANTHROPIC_LOG=info

Or to debug for more verbose logging:

export ANTHROPIC_LOG=debug

Undocumented API functionality

The SDK is typed for convenient usage of the documented API. However, it also supports working with undocumented or not yet supported parts of the API.

Undocumented endpoints

To make requests to undocumented endpoints, you can use the putAdditionalHeader, putAdditionalQueryParam, or putAdditionalBodyProperty methods as described in Undocumented parameters.

Undocumented response properties

To access undocumented response properties, use the _additionalProperties() method as described in Response properties.

Beta features

You can access most beta API features through the beta() method on the client. To check the availability of all of Claude's capabilities and tools, see the build with Claude overview.

For example, to use structured outputs:

import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.beta.messages.StructuredMessageCreateParams;
import com.anthropic.models.messages.Model;

StructuredMessageCreateParams<BookList> createParams = MessageCreateParams.builder()
        .model(Model.CLAUDE_OPUS_4_6)
        .maxTokens(2048)
        .outputFormat(BookList.class)
        .addUserMessage("List some famous late twentieth century novels.")
        .build();

client.beta().messages().create(createParams);

Frequently asked questions

Semantic versioning

This package generally follows SemVer conventions, though certain backwards-incompatible changes may be released as minor versions:

Changes to library internals which are technically public but not intended or documented for external use.
Changes that aren't expected to impact the vast majority of users in practice.

Additional resources

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Installation

Requirements

Quick start

Client configuration

API key setup

Configuration options

Modifying configuration

Async usage

Streaming

Synchronous streaming

Asynchronous streaming

Streaming with message accumulator

Structured outputs

Tool use

Defining tools with annotations

Calling tools

Tool name conversion

Local tool JSON schema validation

Annotating tool classes

Message batches

File uploads

Binary responses

Error handling

Status code mapping

Request IDs

Retries

Timeouts

Long requests

Pagination

Auto-pagination

Manual pagination

Type system

Immutability and builders

Requests and responses

Undocumented parameters

JsonValue creation

Forcibly omitting required parameters

Response properties

Response validation

HTTP client customization

Proxy configuration

HTTPS / SSL configuration

Custom HTTP client

Customized OkHttpClient

Completely custom HTTP client

Platform integrations

Advanced usage

Raw response access

Logging

Jackson compatibility

ProGuard/R8 configuration

Undocumented API functionality

Undocumented endpoints

Undocumented response properties

Beta features

Frequently asked questions

Why doesn't the SDK use plain enum classes?

Why are fields represented using JsonField<T> instead of just plain T?

Why doesn't the SDK use data classes?

Why doesn't the SDK use checked exceptions?

Semantic versioning

Additional resources