Basic usage

Enable compaction by adding the compact_20260112 strategy to context_management.edits in your Messages API request.

curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "anthropic-beta: compact-2026-01-12" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-opus-5",
    "max_tokens": 4096,
    "messages": [
      {
        "role": "user",
        "content": "Help me build a website"
      }
    ],
    "context_management": {
      "edits": [
        {
          "type": "compact_20260112"
        }
      ]
    }
  }'

ant beta:messages create --beta compact-2026-01-12 <<'YAML'
model: claude-opus-5
max_tokens: 4096
messages:
  - role: user
    content: Help me build a website
context_management:
  edits:
    - type: compact_20260112
YAML

client = anthropic.Anthropic()

messages = [{"role": "user", "content": "Help me build a website"}]

response = client.beta.messages.create(
    betas=["compact-2026-01-12"],
    model="claude-opus-5",
    max_tokens=4096,
    messages=messages,
    context_management={"edits": [{"type": "compact_20260112"}]},
)

# Append the response (including any compaction block) to continue the conversation
messages.append({"role": "assistant", "content": response.content})

const client = new Anthropic();

const messages: Anthropic.Beta.Messages.BetaMessageParam[] = [
  { role: "user", content: "Help me build a website" }
];

const response = await client.beta.messages.create({
  betas: ["compact-2026-01-12"],
  model: "claude-opus-5",
  max_tokens: 4096,
  messages,
  context_management: {
    edits: [
      {
        type: "compact_20260112"
      }
    ]
  }
});

// Append the response (including any compaction block) to continue the conversation
messages.push({
  role: "assistant",
  content: response.content
});

AnthropicClient client = new();

var messages = new List<BetaMessageParam>
{
    new() { Role = Role.User, Content = "Help me build a website" }
};

var parameters = new MessageCreateParams
{
    Betas = ["compact-2026-01-12"],
    Model = "claude-opus-5",
    MaxTokens = 4096,
    Messages = messages,
    ContextManagement = new BetaContextManagementConfig
    {
        Edits = [new BetaCompact20260112Edit()]
    }
};

var response = await client.Beta.Messages.Create(parameters);

// Append the response (including any compaction block) to continue the conversation
messages.Add(new BetaMessageParam
{
    Role = Role.Assistant,
    Content = response.Content.Select(block => new BetaContentBlockParam(block.Json)).ToList()
});

Console.WriteLine(response);

client := anthropic.NewClient()

messages := []anthropic.BetaMessageParam{
	anthropic.NewBetaUserMessage(anthropic.NewBetaTextBlock("Help me build a website")),
}

response, err := client.Beta.Messages.New(context.TODO(), anthropic.BetaMessageNewParams{
	Model:     anthropic.ModelClaudeOpus5,
	MaxTokens: 4096,
	Messages:  messages,
	ContextManagement: anthropic.BetaContextManagementConfigParam{
		Edits: []anthropic.BetaContextManagementConfigEditUnionParam{
			{OfCompact20260112: &anthropic.BetaCompact20260112EditParam{}},
		},
	},
	Betas: []anthropic.AnthropicBeta{"compact-2026-01-12"},
})
if err != nil {
	log.Fatal(err)
}

// Append the response (including any compaction block) to continue the conversation
messages = append(messages, response.ToParam())

fmt.Println(response)

import com.anthropic.models.beta.messages.BetaContextManagementConfig;
import com.anthropic.models.beta.messages.BetaCompact20260112Edit;
// ...
        AnthropicClient client = AnthropicOkHttpClient.fromEnv();

        MessageCreateParams params = MessageCreateParams.builder()
            .addBeta("compact-2026-01-12")
            .model("claude-opus-5")
            .maxTokens(4096L)
            .addUserMessage("Help me build a website")
            .contextManagement(BetaContextManagementConfig.builder()
                .addEdit(BetaCompact20260112Edit.builder().build())
                .build())
            .build();

        BetaMessage response = client.beta().messages().create(params);

        // Append the response (including any compaction block) to continue the conversation
        // by including it in the next request's messages
        System.out.println(response);

$client = new Client();

$messages = [
    ['role' => 'user', 'content' => 'Help me build a website']
];

$response = $client->beta->messages->create(
    maxTokens: 4096,
    messages: $messages,
    model: 'claude-opus-5',
    betas: ['compact-2026-01-12'],
    contextManagement: [
        'edits' => [
            ['type' => 'compact_20260112']
        ]
    ]
);

// Append the response (including any compaction block) to continue the conversation
$messages[] = ['role' => 'assistant', 'content' => $response->content];

echo json_encode($response, JSON_PRETTY_PRINT), PHP_EOL;

client = Anthropic::Client.new

messages = [
  { role: "user", content: "Help me build a website" }
]

response = client.beta.messages.create(
  betas: ["compact-2026-01-12"],
  model: "claude-opus-5",
  max_tokens: 4096,
  messages: messages,
  context_management: {
    edits: [{ type: "compact_20260112" }]
  }
)

# Append the response (including any compaction block) to continue the conversation
messages << { role: "assistant", content: response.content }

puts response