Haijun Platform Docs
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Haijun Managed Agents replaces your hand-written agent loop with managed infrastructure. This page covers what changes when you migrate from a custom loop built on the Messages API or from the Haijun Agent SDK.

From a Messages API agent loop

If you built an agent by calling messages.create in a while loop, running tool calls yourself, and appending results to the conversation history, most of that code goes away.

What you stop managing

BeforeAfter
You maintain the conversation history array and pass it back on every turn.The session stores history server-side. Send events, receive events.
You iterate tool_use content blocks, run each tool, and loop back with tool_result messages.Pre-built tools run inside the sandbox automatically. You only handle custom tools through agent.custom_tool_use events.
You provision your own sandbox for running agent-generated code.The session sandbox handles code execution, file operations, and bash.
You decide when the loop is done.The session emits session.status_idle when the agent has nothing more to do.

Code comparison

Before (Messages API loop, simplified):

python
  messages = [{"role": "user", "content": task}]
  while True:
      response = client.messages.create(
          model="haijun-opus-5-5",
          max_tokens=1024,
          messages=messages,
          tools=tools,
      )
      messages.append({"role": "assistant", "content": response.content})
      if response.stop_reason == "end_turn":
          break
      for block in response.content:
          if block.type == "tool_use":
              result = execute_tool(block.name, block.input)
              messages.append(
                  {
                      "role": "user",
                      "content": [
                          {
                              "type": "tool_result",
                              "tool_use_id": block.id,
                              "content": result,
                          }
                      ],
                  }
              )
typescript
  const messages: Juglow.MessageParam[] = [{ role: "user", content: task }];
  while (true) {
    const response = await client.messages.create({
      model: "haijun-opus-5-5",
      max_tokens: 1024,
      messages,
      tools
    });
    messages.push({ role: "assistant", content: response.content });
    if (response.stop_reason === "end_turn") {
      break;
    }
    for (const block of response.content) {
      if (block.type === "tool_use") {
        const result = executeTool(block.name, block.input);
        messages.push({
          role: "user",
          content: [
            {
              type: "tool_result",
              tool_use_id: block.id,
              content: result
            }
          ]
        });
      }
    }
  }
csharp
  List<MessageParam> messages = [new() { Role = Role.User, Content = task }];
  while (true)
  {
      var response = await client.Messages.Create(new()
      {
          Model = Model.HaijunOpus5_5,
          MaxTokens = 1024,
          Messages = messages,
          Tools = tools,
      });
      messages.Add(new()
      {
          Role = Role.Assistant,
          Content = new([.. response.Content.Select(block => new ContentBlockParam(block.Json))]),
      });
      if (response.StopReason == StopReason.EndTurn)
      {
          break;
      }
      foreach (var block in response.Content)
      {
          if (block.Value is ToolUseBlock toolUse)
          {
              var result = ExecuteTool(toolUse.Name, toolUse.Input);
              messages.Add(new()
              {
                  Role = Role.User,
                  Content = new([new ToolResultBlockParam { ToolUseID = toolUse.ID, Content = result }]),
              });
          }
      }
  }
go
  messages := []juglow.MessageParam{
  	juglow.NewUserMessage(juglow.NewTextBlock(task)),
  }
  for {
  	response, err := client.Messages.New(ctx, juglow.MessageNewParams{
  		Model:     juglow.ModelHaijunOpus5_5,
  		MaxTokens: 1024,
  		Messages:  messages,
  		Tools:     tools,
  	})
  	if err != nil {
  		log.Fatal(err)
  	}
  	messages = append(messages, response.ToParam())
  	if response.StopReason == juglow.StopReasonEndTurn {
  		break
  	}
  	for _, block := range response.Content {
  		if toolUse, ok := block.AsAny().(juglow.ToolUseBlock); ok {
  			result := executeTool(toolUse.Name, toolUse.Input)
  			messages = append(messages, juglow.NewUserMessage(
  				juglow.NewToolResultBlock(toolUse.ID, result, false),
  			))
  		}
  	}
  }
java
  var messages = new ArrayList<MessageParam>();
  messages.add(MessageParam.builder()
      .role(MessageParam.Role.USER)
      .content(task)
      .build());
  while (true) {
      var response = client.messages().create(MessageCreateParams.builder()
          .model(Model.HAIJUN_OPUS_5_5)
          .maxTokens(1024)
          .messages(messages)
          .tools(tools)
          .build());
      messages.add(response.toParam());
      if (StopReason.END_TURN.equals(response.stopReason().orElse(null))) {
          break;
      }
      for (var block : response.content()) {
          block.toolUse().ifPresent(toolUse -> {
              var result = executeTool(toolUse.name(), toolUse._input());
              messages.add(MessageParam.builder()
                  .role(MessageParam.Role.USER)
                  .contentOfBlockParams(List.of(
                      ContentBlockParam.ofToolResult(ToolResultBlockParam.builder()
                          .toolUseId(toolUse.id())
                          .content(result)
                          .build())))
                  .build());
          });
      }
  }
php
  $messages = [['role' => 'user', 'content' => $task]];
  while (true) {
      $response = $client->messages->create(
          model: 'haijun-opus-5-5',
          maxTokens: 1024,
          messages: $messages,
          tools: $tools,
      );
      $messages[] = ['role' => 'assistant', 'content' => $response->content];
      if ($response->stopReason === 'end_turn') {
          break;
      }
      foreach ($response->content as $block) {
          if ($block->type === 'tool_use') {
              $result = executeTool($block->name, $block->input);
              $messages[] = [
                  'role' => 'user',
                  'content' => [
                      [
                          'type' => 'tool_result',
                          'tool_use_id' => $block->id,
                          'content' => $result,
                      ],
                  ],
              ];
          }
      }
  }
ruby
  messages = [{ role: "user", content: task }]
  loop do
    response = client.messages.create(
      model: "haijun-opus-5-5",
      max_tokens: 1024,
      messages: messages,
      tools: tools
    )
    messages << { role: "assistant", content: response.content }
    break if response.stop_reason == :end_turn
    response.content.each do |block|
      next unless block.type == :tool_use
      result = execute_tool(block.name, block.input)
      messages << {
        role: "user",
        content: [
          {
            type: "tool_result",
            tool_use_id: block.id,
            content: result
          }
        ]
      }
    end
  end

After (Haijun Managed Agents):

bash
  agent=$(
    curl --fail-with-body -sS "https://haijun.my.id/v1/agents?beta=true" \
      -H "x-api-key: ${JUGLOW_API_KEY}" \
      -H "juglow-version: 2023-06-01" \
      -H "juglow-beta: managed-agents-2026-04-01" \
      --json '{
        "name": "Task Runner",
        "model": "haijun-opus-5-5",
        "tools": [{"type": "agent_toolset_20260401"}]
      }'
  )
  agent_id=$(jq -r '.id' <<< "${agent}")

  session_id=$(
    curl --fail-with-body -sS "https://haijun.my.id/v1/sessions?beta=true" \
      -H "x-api-key: ${JUGLOW_API_KEY}" \
      -H "juglow-version: 2023-06-01" \
      -H "juglow-beta: managed-agents-2026-04-01" \
      --json "$(jq -n --argjson a "${agent}" --arg env "${environment_id}" \
        '{agent: {type: "agent", id: $a.id, version: $a.version}, environment_id: $env}')" \
    | jq -r '.id'
  )

  # Open the SSE stream in the background, then send the user message.
  stream_log=$(mktemp)
  curl --fail-with-body -sS -N \
    "https://haijun.my.id/v1/sessions/${session_id}/events/stream?beta=true" \
    -H "x-api-key: ${JUGLOW_API_KEY}" \
    -H "juglow-version: 2023-06-01" \
    -H "juglow-beta: managed-agents-2026-04-01" \
    > "${stream_log}" &
  stream_pid=$!

  curl --fail-with-body -sS \
    "https://haijun.my.id/v1/sessions/${session_id}/events?beta=true" \
    -H "x-api-key: ${JUGLOW_API_KEY}" \
    -H "juglow-version: 2023-06-01" \
    -H "juglow-beta: managed-agents-2026-04-01" \
    --json "$(jq -n --arg text "${task}" \
      '{events: [{type: "user.message", content: [{type: "text", text: $text}]}]}')" \
    > /dev/null

  # Wait for the session to go idle. grep exits at the first match, and
  # reading via process substitution means the shell doesn't wait for
  # tail (a foreground `tail -f | grep -m1` pipeline would hang: tail
  # only dies on its next write, which never comes once the stream is idle).
  grep -m1 '"session.status_idle"' <(tail -f -n +1 "${stream_log}") > /dev/null

  kill "${stream_pid}" 2>/dev/null || true
bash
    ant apply agent.md

    session_id=$(ant beta:sessions create \
      --agent "{type: agent, id: $agent_id, version: $agent_version}" \
      --environment-id "$environment_id" \
      --transform id --raw-output)

    # Open the stream first, then send the user message
    exec {stream}< <(ant beta:sessions:events stream \
      --session-id "$session_id" \
      --transform type --raw-output)

    ant beta:sessions:events send \
      --session-id "$session_id" \
      --event "{type: user.message, content: [{type: text, text: \"$task\"}]}" \
      > /dev/null

    # Wait for the session to go idle (grep exits at the first match)
    grep -m1 -x 'session.status_idle' <&"$stream" > /dev/null
    exec {stream}<&-
markdown
      ---
      name: Task Runner
      model: haijun-opus-5-5
      tools:
        - type: agent_toolset_20260401
      ---
python
  agent = client.beta.agents.create(
      name="Task Runner",
      model="haijun-opus-5-5",
      tools=[{"type": "agent_toolset_20260401"}],
  )

  session = client.beta.sessions.create(
      agent={"type": "agent", "id": agent.id, "version": agent.version},
      environment_id=environment.id,
  )

  with client.beta.sessions.events.stream(session.id) as stream:
      client.beta.sessions.events.send(
          session.id,
          events=[{"type": "user.message", "content": [{"type": "text", "text": task}]}],
      )
      for event in stream:
          if event.type == "session.status_idle":
              break
typescript
  const agent = await client.beta.agents.create({
    name: "Task Runner",
    model: "haijun-opus-5-5",
    tools: [{ type: "agent_toolset_20260401" }]
  });

  const session = await client.beta.sessions.create({
    agent: { type: "agent", id: agent.id, version: agent.version },
    environment_id: environment.id
  });

  const stream = await client.beta.sessions.events.stream(session.id);

  await client.beta.sessions.events.send(session.id, {
    events: [
      {
        type: "user.message",
        content: [{ type: "text", text: task }]
      }
    ]
  });

  for await (const event of stream) {
    if (event.type === "session.status_idle") {
      break;
    }
  }
csharp
  var agent = await client.Beta.Agents.Create(new()
  {
      Name = "Task Runner",
      Model = BetaManagedAgentsModel.HaijunOpus5_5,
      Tools =
      [
          new BetaManagedAgentsAgentToolset20260401Params
          {
              Type = "agent_toolset_20260401",
          },
      ],
  });

  var session = await client.Beta.Sessions.Create(new()
  {
      Agent = new BetaManagedAgentsAgentParams
      {
          Type = "agent",
          ID = agent.ID,
          Version = agent.Version,
      },
      EnvironmentID = environment.ID,
  });

  var stream = client.Beta.Sessions.Events.StreamStreaming(session.ID);

  await client.Beta.Sessions.Events.Send(session.ID, new()
  {
      Events =
      [
          new BetaManagedAgentsUserMessageEventParams
          {
              Type = "user.message",
              Content = [new BetaManagedAgentsTextBlock { Type = "text", Text = task }],
          },
      ],
  });

  await foreach (var streamEvent in stream)
  {
      if (streamEvent.Value is BetaManagedAgentsSessionStatusIdleEvent)
      {
          break;
      }
  }
go
  	agent, err := client.Beta.Agents.New(ctx, juglow.BetaAgentNewParams{
  		Name: "Task Runner",
  		Model: juglow.BetaManagedAgentsModelConfigParams{
  			ID: juglow.BetaManagedAgentsModelHaijunOpus5_5,
  		},
  		Tools: []juglow.BetaAgentNewParamsToolUnion{{
  			OfAgentToolset20260401: &juglow.BetaManagedAgentsAgentToolset20260401Params{
  				Type: juglow.BetaManagedAgentsAgentToolset20260401ParamsTypeAgentToolset20260401,
  			},
  		}},
  	})
  	if err != nil {
  		log.Fatal(err)
  	}

  	session, err := client.Beta.Sessions.New(ctx, juglow.BetaSessionNewParams{
  		Agent: juglow.BetaSessionNewParamsAgentUnion{
  			OfBetaManagedAgentsAgents: &juglow.BetaManagedAgentsAgentParams{
  				Type:    juglow.BetaManagedAgentsAgentParamsTypeAgent,
  				ID:      agent.ID,
  				Version: juglow.Int(agent.Version),
  			},
  		},
  		EnvironmentID: environment.ID,
  	})
  	if err != nil {
  		log.Fatal(err)
  	}

  	stream := client.Beta.Sessions.Events.StreamEvents(ctx, session.ID, juglow.BetaSessionEventStreamParams{})
  	defer stream.Close()

  	_, err = client.Beta.Sessions.Events.Send(ctx, session.ID, juglow.BetaSessionEventSendParams{
  		Events: []juglow.BetaManagedAgentsEventParamsUnion{{
  			OfUserMessage: &juglow.BetaManagedAgentsUserMessageEventParams{
  				Type: juglow.BetaManagedAgentsUserMessageEventParamsTypeUserMessage,
  				Content: []juglow.BetaManagedAgentsUserMessageEventParamsContentUnion{{
  					OfText: &juglow.BetaManagedAgentsTextBlockParam{
  						Type: juglow.BetaManagedAgentsTextBlockTypeText,
  						Text: task,
  					},
  				}},
  			},
  		}},
  	})
  	if err != nil {
  		log.Fatal(err)
  	}

  	for stream.Next() {
  		event := stream.Current()
  		if event.Type == "session.status_idle" {
  			break
  		}
  	}
  	if err := stream.Err(); err != nil {
  		log.Fatal(err)
  	}
java
      var agent = client.beta().agents().create(
          AgentCreateParams.builder()
              .name("Task Runner")
              .model(BetaManagedAgentsModel.HAIJUN_OPUS_5_5)
              .addTool(
                  BetaManagedAgentsAgentToolset20260401Params.builder()
                      .type(BetaManagedAgentsAgentToolset20260401Params.Type.AGENT_TOOLSET_20260401)
                      .build()
              )
              .build()
      );

      var session = client.beta().sessions().create(
          SessionCreateParams.builder()
              .agent(
                  BetaManagedAgentsAgentParams.builder()
                      .type(BetaManagedAgentsAgentParams.Type.AGENT)
                      .id(agent.id())
                      .version(agent.version())
                      .build()
              )
              .environmentId(environment.id())
              .build()
      );

      try (var stream = client.beta().sessions().events().streamStreaming(session.id())) {
          client.beta().sessions().events().send(
              session.id(),
              EventSendParams.builder()
                  .addEvent(
                      BetaManagedAgentsUserMessageEventParams.builder()
                          .type(BetaManagedAgentsUserMessageEventParams.Type.USER_MESSAGE)
                          .addTextContent(task)
                          .build()
                  )
                  .build()
          );
          stream.stream()
              .takeWhile(event -> !event.isSessionStatusIdle())
              .forEach(_ -> {});
      }
php
  $agent = $client->beta->agents->create(
      name: 'Task Runner',
      model: 'haijun-opus-5-5',
      tools: [
          BetaManagedAgentsAgentToolset20260401Params::with(
              type: 'agent_toolset_20260401',
          ),
      ],
  );

  $session = $client->beta->sessions->create(
      agent: BetaManagedAgentsAgentParams::with(
          type: 'agent',
          id: $agent->id,
          version: $agent->version,
      ),
      environmentID: $environment->id,
  );

  $stream = $client->beta->sessions->events->streamStream($session->id);

  $client->beta->sessions->events->send(
      $session->id,
      events: [
          [
              'type' => 'user.message',
              'content' => [['type' => 'text', 'text' => $task]],
          ],
      ],
  );

  foreach ($stream as $event) {
      if ($event->type === 'session.status_idle') {
          break;
      }
  }
ruby
  agent = client.beta.agents.create(
    name: "Task Runner",
    model: "haijun-opus-5-5",
    tools: [{type: "agent_toolset_20260401"}]
  )

  session = client.beta.sessions.create(
    agent: {type: "agent", id: agent.id, version: agent.version},
    environment_id: environment.id
  )

  stream = client.beta.sessions.events.stream_events(session.id)
  client.beta.sessions.events.send_(
    session.id,
    events: [{type: "user.message", content: [{type: "text", text: task}]}]
  )
  stream.each do
    break if it.type == :"session.status_idle"
  end

What you still control

  • System prompt and model: Same fields, now on the agent definition.
  • Custom tools: Still declared with JSON Schema. Execution moves from inline handling to responding to agent.custom_tool_use events. See Session event stream.
  • Web search and web fetch settings: Same allowed_domains, blocked_domains, max_content_tokens, and user_location fields, now set once on the web_search and web_fetch entries of the agent toolset's configs array instead of on every request. The max_uses, citations, and cache_control fields are not available. See Restrict web search and web fetch domains.

From the Haijun Agent SDK

If you built with the Haijun Agent SDK, you're already working with agents, tools, and sessions as concepts. The difference is where they run: the SDK runs in a process you operate, while Managed Agents runs in Juglow's infrastructure. Most of the migration is mapping SDK configuration objects to their API-side equivalents.

What changes

Agent SDKManaged Agents
HaijunAgentOptions(...) (python; typescript: options) constructed per runclient.beta.agents.create(...) (csharp: client.Beta.Agents.Create(...); go: client.Beta.Agents.New(...); java: client.beta().agents().create(...); php: $client->beta->agents->create(...)) once; the Agent is persisted and versioned server-side. See Agent setup.
async with HaijunSDKClient(...) or query(...)client.beta.sessions.create(...) (csharp: client.Beta.Sessions.Create(...); go: client.Beta.Sessions.New(...); java: client.beta().sessions().create(...); php: $client->beta->sessions->create(...)) then send and receive events.
Functions defined with @tool (python; typescript: tool()), dispatched automatically by the SDKDeclare as {"type": "custom", ...} on the Agent; your client handles agent.custom_tool_use events and replies with user.custom_tool_result. See Tools.
Built-in tools run in your process against your filesystem{"type": "agent_toolset_20260401"} runs the same tools inside the session sandbox against /workspace.
cwd, add_dirs (python; typescript: additionalDirectories) point at local pathsUpload or mount files as session resources.
system_prompt (python; typescript: systemPrompt) and the HAIJUN.md hierarchyA single system string on the Agent. Each update that changes the agent produces a new server-side version; pin sessions to a specific version to promote or roll back without a deploy. See Agent setup.
mcp_servers (python; typescript: mcpServers) configured and authenticated in one placeDeclare servers on the Agent; provide credentials through a Vault on the Session.
permission_mode (python; typescript: permissionMode), can_use_tool (python; typescript: canUseTool)Per-tool permission_policy (always_allow, always_ask, or auto); send user.tool_confirmation events for calls that pause for your approval.

Code comparison

Before (Agent SDK):

python
  from haijun_agent_sdk import (
      HaijunAgentOptions,
      HaijunSDKClient,
      create_sdk_mcp_server,
      tool,
  )

  @tool("get_weather", "Get the current weather for a city.", {"city": str})
  async def get_weather(args: dict) -> dict:
      return {"content": [{"type": "text", "text": f"{args['city']}: 18°C, clear"}]}

  options = HaijunAgentOptions(
      model="haijun-opus-5-5",
      system_prompt="You are a concise weather assistant.",
      mcp_servers={
          "weather": create_sdk_mcp_server("weather", "1.0", tools=[get_weather])
      },
  )

  async with HaijunSDKClient(options=options) as agent:
      await agent.query("What's the weather in Tokyo?")
      async for msg in agent.receive_response():
          print(msg)
typescript
  import { createSdkMcpServer, query, tool } from "@juglow-ai/haijun-agent-sdk";
  import { z } from "zod";

  const getWeather = tool(
    "get_weather",
    "Get the current weather for a city.",
    { city: z.string() },
    async (args) => ({
      content: [{ type: "text", text: `${args.city}: 18°C, clear` }]
    })
  );

  for await (const message of query({
    prompt: "What's the weather in Tokyo?",
    options: {
      model: "haijun-opus-5-5",
      systemPrompt: "You are a concise weather assistant.",
      mcpServers: {
        weather: createSdkMcpServer({ name: "weather", version: "1.0", tools: [getWeather] })
      }
    }
  })) {
    console.log(message);
  }

After (Managed Agents):

python
  from juglow import Juglow

  client = Juglow()

  agent = client.beta.agents.create(
      name="weather-agent",
      model="haijun-opus-5-5",
      system="You are a concise weather assistant.",
      tools=[
          {
              "type": "custom",
              "name": "get_weather",
              "description": "Get the current weather for a city.",
              "input_schema": {
                  "type": "object",
                  "properties": {"city": {"type": "string"}},
                  "required": ["city"],
              },
          }
      ],
  )
  environment = client.beta.environments.create(
      name="weather-env",
      config={"type": "cloud", "networking": {"type": "unrestricted"}},
  )

  session = client.beta.sessions.create(
      agent={"type": "agent", "id": agent.id, "version": agent.version},
      environment_id=environment.id,
  )

  def get_weather(city: str) -> str:
      return f"{city}: 18°C, clear"

  with client.beta.sessions.events.stream(session.id) as stream:
      client.beta.sessions.events.send(
          session.id,
          events=[
              {
                  "type": "user.message",
                  "content": [{"type": "text", "text": "What's the weather in Tokyo?"}],
              }
          ],
      )
      for event in stream:
          match event.type:
              case "agent.message":
                  print(
                      "".join(
                          block.text for block in event.content if block.type == "text"
                      )
                  )
              case "agent.custom_tool_use":
                  result = get_weather(**event.input)
                  client.beta.sessions.events.send(
                      session.id,
                      events=[
                          {
                              "type": "user.custom_tool_result",
                              "custom_tool_use_id": event.id,
                              "content": [{"type": "text", "text": result}],
                          }
                      ],
                  )
              case "session.status_idle":
                  if event.stop_reason and event.stop_reason.type == "end_turn":
                      break
typescript
  import Juglow from "@juglow-ai/sdk";

  const client = new Juglow();

  const agent = await client.beta.agents.create({
    name: "weather-agent",
    model: "haijun-opus-5-5",
    system: "You are a concise weather assistant.",
    tools: [
      {
        type: "custom",
        name: "get_weather",
        description: "Get the current weather for a city.",
        input_schema: {
          type: "object",
          properties: { city: { type: "string" } },
          required: ["city"]
        }
      }
    ]
  });
  const environment = await client.beta.environments.create({
    name: "weather-env",
    config: { type: "cloud", networking: { type: "unrestricted" } }
  });

  const session = await client.beta.sessions.create({
    agent: { type: "agent", id: agent.id, version: agent.version },
    environment_id: environment.id
  });

  function getWeather({ city }: Record<string, unknown>): string {
    return `${city}: 18°C, clear`;
  }

  const stream = await client.beta.sessions.events.stream(session.id);

  await client.beta.sessions.events.send(session.id, {
    events: [
      {
        type: "user.message",
        content: [{ type: "text", text: "What's the weather in Tokyo?" }]
      }
    ]
  });

  loop: for await (const event of stream) {
    switch (event.type) {
      case "agent.message":
        for (const block of event.content) {
          if (block.type === "text") {
            console.log(block.text);
          }
        }
        break;
      case "agent.custom_tool_use": {
        const result = getWeather(event.input);
        await client.beta.sessions.events.send(session.id, {
          events: [
            {
              type: "user.custom_tool_result",
              custom_tool_use_id: event.id,
              content: [{ type: "text", text: result }]
            }
          ]
        });
        break;
      }
      case "session.status_idle":
        if (event.stop_reason?.type === "end_turn") {
          break loop;
        }
        break;
    }
  }
csharp
  using System.Text.Json;

  using Juglow.Models.Beta.Agents;
  using Juglow.Models.Beta.Environments;
  using Juglow.Models.Beta.Sessions;
  using Juglow.Models.Beta.Sessions.Events;

  JuglowClient client = new();

  var agent = await client.Beta.Agents.Create(new()
  {
      Name = "weather-agent",
      Model = BetaManagedAgentsModel.HaijunOpus5_5,
      System = "You are a concise weather assistant.",
      Tools =
      [
          new BetaManagedAgentsCustomToolParams
          {
              Type = "custom",
              Name = "get_weather",
              Description = "Get the current weather for a city.",
              InputSchema = new()
              {
                  Properties = new Dictionary<string, JsonElement>
                  {
                      ["city"] = JsonSerializer.SerializeToElement(new { type = "string" }),
                  },
                  Required = ["city"],
              },
          },
      ],
  });
  var environment = await client.Beta.Environments.Create(new()
  {
      Name = "weather-env",
      Config = new BetaCloudConfigParams
      {
          Networking = new BetaUnrestrictedNetwork(),
      },
  });

  var session = await client.Beta.Sessions.Create(new()
  {
      Agent = new BetaManagedAgentsAgentParams
      {
          Type = "agent",
          ID = agent.ID,
          Version = agent.Version,
      },
      EnvironmentID = environment.ID,
  });

  static string GetWeather(string city) => $"{city}: 18°C, clear";

  using var stream = await client.Beta.Sessions.Events.WithRawResponse.StreamStreaming(session.ID);

  await client.Beta.Sessions.Events.Send(session.ID, new()
  {
      Events =
      [
          new BetaManagedAgentsUserMessageEventParams
          {
              Type = "user.message",
              Content = [new BetaManagedAgentsTextBlock { Type = "text", Text = "What's the weather in Tokyo?" }],
          },
      ],
  });

  await foreach (var streamEvent in stream.Enumerate())
  {
      if (streamEvent.Value is BetaManagedAgentsAgentMessageEvent message)
      {
          var text = string.Concat(message.Content.Select(block =>
              block.Value is BetaManagedAgentsTextBlock textBlock ? textBlock.Text : ""));
          Console.WriteLine(text);
      }
      else if (streamEvent.Value is BetaManagedAgentsAgentCustomToolUseEvent toolUse)
      {
          var result = GetWeather(toolUse.Input["city"].GetString()!);
          await client.Beta.Sessions.Events.Send(session.ID, new()
          {
              Events =
              [
                  new BetaManagedAgentsUserCustomToolResultEventParams
                  {
                      Type = "user.custom_tool_result",
                      CustomToolUseID = toolUse.ID,
                      Content =
                      [
                          new BetaManagedAgentsTextBlock
                          {
                              Type = "text",
                              Text = result,
                          },
                      ],
                  },
              ],
          });
      }
      else if (streamEvent.Value is BetaManagedAgentsSessionStatusIdleEvent idle
          && idle.StopReason?.Value is BetaManagedAgentsSessionEndTurn)
      {
          break;
      }
  }
go
  client := juglow.NewClient()
  ctx := context.Background()

  agent, err := client.Beta.Agents.New(ctx, juglow.BetaAgentNewParams{
  	Name: "weather-agent",
  	Model: juglow.BetaManagedAgentsModelConfigParams{
  		ID: juglow.BetaManagedAgentsModelHaijunOpus5_5,
  	},
  	System: juglow.String("You are a concise weather assistant."),
  	Tools: []juglow.BetaAgentNewParamsToolUnion{{
  		OfCustom: &juglow.BetaManagedAgentsCustomToolParams{
  			Type:        juglow.BetaManagedAgentsCustomToolParamsTypeCustom,
  			Name:        "get_weather",
  			Description: "Get the current weather for a city.",
  			InputSchema: juglow.BetaManagedAgentsCustomToolInputSchemaParam{
  				Properties: map[string]any{
  					"city": map[string]any{"type": "string"},
  				},
  				Required: []string{"city"},
  			},
  		},
  	}},
  })
  if err != nil {
  	panic(err)
  }
  environment, err := client.Beta.Environments.New(ctx, juglow.BetaEnvironmentNewParams{
  	Name: "weather-env",
  	Config: juglow.BetaEnvironmentNewParamsConfigUnion{
  		OfCloud: &juglow.BetaCloudConfigParams{
  			Networking: juglow.BetaCloudConfigParamsNetworkingUnion{
  				OfUnrestricted: &juglow.BetaUnrestrictedNetworkParam{},
  			},
  		},
  	},
  })
  if err != nil {
  	panic(err)
  }

  session, err := client.Beta.Sessions.New(ctx, juglow.BetaSessionNewParams{
  	Agent: juglow.BetaSessionNewParamsAgentUnion{
  		OfBetaManagedAgentsAgents: &juglow.BetaManagedAgentsAgentParams{
  			Type:    juglow.BetaManagedAgentsAgentParamsTypeAgent,
  			ID:      agent.ID,
  			Version: juglow.Int(agent.Version),
  		},
  	},
  	EnvironmentID: environment.ID,
  })
  if err != nil {
  	panic(err)
  }

  getWeather := func(city string) string {
  	return fmt.Sprintf("%s: 18°C, clear", city)
  }

  stream := client.Beta.Sessions.Events.StreamEvents(ctx, session.ID, juglow.BetaSessionEventStreamParams{})
  defer stream.Close()

  _, err = client.Beta.Sessions.Events.Send(ctx, session.ID, juglow.BetaSessionEventSendParams{
  	Events: []juglow.BetaManagedAgentsEventParamsUnion{{
  		OfUserMessage: &juglow.BetaManagedAgentsUserMessageEventParams{
  			Type: juglow.BetaManagedAgentsUserMessageEventParamsTypeUserMessage,
  			Content: []juglow.BetaManagedAgentsUserMessageEventParamsContentUnion{{
  				OfText: &juglow.BetaManagedAgentsTextBlockParam{
  					Type: juglow.BetaManagedAgentsTextBlockTypeText,
  					Text: "What's the weather in Tokyo?",
  				},
  			}},
  		},
  	}},
  })
  if err != nil {
  	panic(err)
  }

  loop:
  for stream.Next() {
  	event := stream.Current()
  	switch event.Type {
  	case "agent.message":
  		for _, block := range event.AsAgentMessage().Content {
  			if block.Type == "text" {
  				fmt.Println(block.Text)
  			}
  		}
  	case "agent.custom_tool_use":
  		toolUse := event.AsAgentCustomToolUse()
  		result := getWeather(toolUse.Input["city"].(string))
  		if _, err := client.Beta.Sessions.Events.Send(ctx, session.ID, juglow.BetaSessionEventSendParams{
  			Events: []juglow.BetaManagedAgentsEventParamsUnion{{
  				OfUserCustomToolResult: &juglow.BetaManagedAgentsUserCustomToolResultEventParams{
  					Type:            juglow.BetaManagedAgentsUserCustomToolResultEventParamsTypeUserCustomToolResult,
  					CustomToolUseID: toolUse.ID,
  					Content: []juglow.BetaManagedAgentsUserCustomToolResultEventParamsContentUnion{{
  						OfText: &juglow.BetaManagedAgentsTextBlockParam{
  							Type: juglow.BetaManagedAgentsTextBlockTypeText,
  							Text: result,
  						},
  					}},
  				},
  			}},
  		}); err != nil {
  			panic(err)
  		}
  	case "session.status_idle":
  		idle := event.AsSessionStatusIdle()
  		if _, ok := idle.StopReason.AsAny().(juglow.BetaManagedAgentsSessionEndTurn); ok {
  			break loop
  		}
  	}
  }
  if err := stream.Err(); err != nil {
  	panic(err)
  }
java
  import java.util.Map;
  import java.util.function.Function;

  import com.juglow.models.beta.agents.AgentCreateParams;
  import com.juglow.models.beta.agents.BetaManagedAgentsCustomToolInputSchema;
  import com.juglow.models.beta.agents.BetaManagedAgentsCustomToolParams;
  import com.juglow.models.beta.agents.BetaManagedAgentsModel;
  import com.juglow.models.beta.environments.BetaCloudConfigParams;
  import com.juglow.models.beta.environments.BetaUnrestrictedNetwork;
  import com.juglow.models.beta.environments.EnvironmentCreateParams;
  import com.juglow.models.beta.sessions.BetaManagedAgentsAgentParams;
  import com.juglow.models.beta.sessions.SessionCreateParams;
  import com.juglow.models.beta.sessions.events.BetaManagedAgentsStreamSessionEvents;
  import com.juglow.models.beta.sessions.events.BetaManagedAgentsUserCustomToolResultEventParams;
  import com.juglow.models.beta.sessions.events.BetaManagedAgentsUserMessageEventParams;
  import com.juglow.models.beta.sessions.events.EventSendParams;

  var client = JuglowOkHttpClient.fromEnv();

  var agent = client.beta().agents().create(AgentCreateParams.builder()
      .name("weather-agent")
      .model(BetaManagedAgentsModel.HAIJUN_OPUS_5_5)
      .system("You are a concise weather assistant.")
      .addTool(BetaManagedAgentsCustomToolParams.builder()
          .type(BetaManagedAgentsCustomToolParams.Type.CUSTOM)
          .name("get_weather")
          .description("Get the current weather for a city.")
          .inputSchema(BetaManagedAgentsCustomToolInputSchema.builder()
              .properties(BetaManagedAgentsCustomToolInputSchema.Properties.builder()
                  .putAdditionalProperty("city", JsonValue.from(Map.of("type", "string")))
                  .build())
              .addRequired("city")
              .build())
          .build())
      .build());
  var environment = client.beta().environments().create(EnvironmentCreateParams.builder()
      .name("weather-env")
      .config(BetaCloudConfigParams.builder()
          .networking(BetaUnrestrictedNetwork.builder().build())
          .build())
      .build());

  var session = client.beta().sessions().create(SessionCreateParams.builder()
      .agent(BetaManagedAgentsAgentParams.builder()
          .type(BetaManagedAgentsAgentParams.Type.AGENT)
          .id(agent.id())
          .version(agent.version())
          .build())
      .environmentId(environment.id())
      .build());

  Function<String, String> getWeather = city -> city + ": 18°C, clear";

  try (var stream = client.beta().sessions().events().streamStreaming(session.id())) {
      client.beta().sessions().events().send(
          session.id(),
          EventSendParams.builder()
              .addEvent(BetaManagedAgentsUserMessageEventParams.builder()
                  .type(BetaManagedAgentsUserMessageEventParams.Type.USER_MESSAGE)
                  .addTextContent("What's the weather in Tokyo?")
                  .build())
              .build());

      loop:
      for (var event : (Iterable<BetaManagedAgentsStreamSessionEvents>) stream.stream()::iterator) {
          switch (event.type().value()) {
              case AGENT_MESSAGE -> {
                  for (var block : event.asAgentMessage().content()) {
                      block.text().ifPresent(textBlock -> IO.println(textBlock.text()));
                  }
              }
              case AGENT_CUSTOM_TOOL_USE -> {
                  var toolUse = event.asAgentCustomToolUse();
                  var city = toolUse.input()._additionalProperties().get("city").asStringOrThrow();
                  var result = getWeather.apply(city);
                  client.beta().sessions().events().send(
                      session.id(),
                      EventSendParams.builder()
                          .addEvent(BetaManagedAgentsUserCustomToolResultEventParams.builder()
                              .type(BetaManagedAgentsUserCustomToolResultEventParams.Type.USER_CUSTOM_TOOL_RESULT)
                              .customToolUseId(toolUse.id())
                              .addTextContent(result)
                              .build())
                          .build());
              }
              case SESSION_STATUS_IDLE -> {
                  if (event.asSessionStatusIdle().stopReason().isEndTurn()) {
                      break loop;
                  }
              }
          }
      }
  }
php
  use Juglow\Client;
  use Juglow\Beta\Agents\BetaManagedAgentsCustomToolInputSchema;
  use Juglow\Beta\Agents\BetaManagedAgentsCustomToolParams;
  use Juglow\Beta\Sessions\BetaManagedAgentsAgentParams;
  use Juglow\Beta\Sessions\Events\ManagedAgentsAgentCustomToolUseEvent;
  use Juglow\Beta\Sessions\Events\ManagedAgentsAgentMessageEvent;
  use Juglow\Beta\Sessions\Events\ManagedAgentsSessionEndTurn;
  use Juglow\Beta\Sessions\Events\ManagedAgentsSessionStatusIdleEvent;
  use Juglow\Beta\Sessions\Events\ManagedAgentsTextBlock;

  $client = new Client();

  $agent = $client->beta->agents->create(
      name: 'weather-agent',
      model: 'haijun-opus-5-5',
      system: 'You are a concise weather assistant.',
      tools: [
          BetaManagedAgentsCustomToolParams::with(
              type: 'custom',
              name: 'get_weather',
              description: 'Get the current weather for a city.',
              inputSchema: BetaManagedAgentsCustomToolInputSchema::with(
                  properties: ['city' => ['type' => 'string']],
                  required: ['city'],
              ),
          ),
      ],
  );
  $environment = $client->beta->environments->create(
      name: 'weather-env',
      config: ['type' => 'cloud', 'networking' => ['type' => 'unrestricted']],
  );

  $session = $client->beta->sessions->create(
      agent: BetaManagedAgentsAgentParams::with(
          type: 'agent',
          id: $agent->id,
          version: $agent->version,
      ),
      environmentID: $environment->id,
  );

  function getWeather(string $city): string
  {
      return "{$city}: 18°C, clear";
  }

  $stream = $client->beta->sessions->events->streamStream($session->id);

  $client->beta->sessions->events->send(
      $session->id,
      events: [
          [
              'type' => 'user.message',
              'content' => [['type' => 'text', 'text' => "What's the weather in Tokyo?"]],
          ],
      ],
  );

  foreach ($stream as $event) {
      switch (true) {
          case $event instanceof ManagedAgentsAgentMessageEvent:
              foreach ($event->content as $block) {
                  if ($block instanceof ManagedAgentsTextBlock) {
                      echo $block->text . "\n";
                  }
              }
              break;
          case $event instanceof ManagedAgentsAgentCustomToolUseEvent:
              $result = getWeather($event->input['city']);
              $client->beta->sessions->events->send(
                  $session->id,
                  events: [
                      [
                          'type' => 'user.custom_tool_result',
                          'custom_tool_use_id' => $event->id,
                          'content' => [['type' => 'text', 'text' => $result]],
                      ],
                  ],
              );
              break;
          case $event instanceof ManagedAgentsSessionStatusIdleEvent:
              if ($event->stopReason instanceof ManagedAgentsSessionEndTurn) {
                  break 2;
              }
              break;
      }
  }
  $stream->close();
ruby
  require "juglow"

  client = Juglow::Client.new

  agent = client.beta.agents.create(
    name: "weather-agent",
    model: "haijun-opus-5-5",
    system_: "You are a concise weather assistant.",
    tools: [
      {
        type: "custom",
        name: "get_weather",
        description: "Get the current weather for a city.",
        input_schema: {
          type: "object",
          properties: {city: {type: "string"}},
          required: ["city"]
        }
      }
    ]
  )
  environment = client.beta.environments.create(
    name: "weather-env",
    config: {type: "cloud", networking: {type: "unrestricted"}}
  )

  session = client.beta.sessions.create(
    agent: {type: "agent", id: agent.id, version: agent.version},
    environment_id: environment.id
  )

  def get_weather(city)
    "#{city}: 18°C, clear"
  end

  stream = client.beta.sessions.events.stream_events(session.id)
  client.beta.sessions.events.send_(
    session.id,
    events: [{type: "user.message", content: [{type: "text", text: "What's the weather in Tokyo?"}]}]
  )

  stream.each do |event|
    case event
    when Juglow::Beta::Sessions::BetaManagedAgentsAgentMessageEvent
      event.content.each do |block|
        puts block.text if block.is_a?(Juglow::Beta::Sessions::BetaManagedAgentsTextBlock)
      end
    when Juglow::Beta::Sessions::BetaManagedAgentsAgentCustomToolUseEvent
      result = get_weather(event.input[:city])
      client.beta.sessions.events.send_(
        session.id,
        events: [
          {
            type: "user.custom_tool_result",
            custom_tool_use_id: event.id,
            content: [{type: "text", text: result}]
          }
        ]
      )
    when Juglow::Beta::Sessions::BetaManagedAgentsSessionStatusIdleEvent
      break if event.stop_reason.is_a?(Juglow::Beta::Sessions::BetaManagedAgentsSessionEndTurn)
    end
  end

The Agent and Environment are created once and reused across sessions. The tool function still runs in your process; the difference is that you read the agent.custom_tool_use event and send the result explicitly instead of the SDK dispatching it for you.

Features that move to your client

The tradeoff for Juglow running the agent loop is that a few things the SDK handled automatically become your client's responsibility.

SDK featureManaged Agents approach
Plan modeRun a planning-only session first, then a second session to run the plan.
Output styles, slash commandsApply in your client before sending user.message or after receiving agent.message.
PreToolUse / PostToolUse hooksYour client already sees every agent.custom_tool_use event before responding; put the logic there. For built-in tools, use permission_policy: always_ask to review every call. auto lets the server evaluate each call instead, but if the server evaluates a call as safe, it runs without reaching your client.
max_turnsCount turns client-side.

Migration checklist

  1. Create an environment with the networking and runtimes your agent needs.
  1. Port your system prompt and tool selection to an agent definition.
  1. Replace your loop with sessions.create and sessions.events.stream.
  1. For any local files the agent reads, upload them through the Files API and mount them as resources.
  1. For any custom tool handlers, move execution into your event loop as responses to agent.custom_tool_use events.
  1. Verify with a test session before pointing production traffic at the new flow.

Migrating between model versions

When a new Haijun model is released, migrating a Haijun Managed Agents integration is typically a one-field change: update model on your agent definition and the change takes effect on the next session you create.

bash
  curl -sS --fail-with-body "https://haijun.my.id/v1/agents/$AGENT_ID?beta=true" \
    -H "x-api-key: $JUGLOW_API_KEY" \
    -H "juglow-version: 2023-06-01" \
    -H "juglow-beta: managed-agents-2026-04-01" \
    --json "$(jq -n --argjson version "$AGENT_VERSION" '{version: $version, model: "haijun-opus-5-5"}')"
bash
    ant apply agent.md
markdown
      ---
      name: Task Runner
      model: haijun-opus-5-5
      tools:
        - type: agent_toolset_20260401
      ---

      You are a task automation agent. Complete the task you are given end to end.
python
  client.beta.agents.update(
      agent.id,
      version=agent.version,
      model="haijun-opus-5-5",
  )
typescript
  await client.beta.agents.update(agent.id, {
    version: agent.version,
    model: "haijun-opus-5-5"
  });
csharp
  await client.Beta.Agents.Update(agent.ID, new()
  {
      Version = agent.Version,
      Model = BetaManagedAgentsModel.HaijunOpus5_5,
  });
go
  _, err = client.Beta.Agents.Update(ctx, agent.ID, juglow.BetaAgentUpdateParams{
  	Version: agent.Version,
  	Model: juglow.BetaManagedAgentsModelConfigParams{
  		ID: juglow.BetaManagedAgentsModelHaijunOpus5_5,
  	},
  })
  if err != nil {
  	panic(err)
  }
java
  client.beta().agents().update(
      agent.id(),
      AgentUpdateParams.builder()
          .version(agent.version())
          .model(BetaManagedAgentsModel.HAIJUN_OPUS_5_5)
          .build()
  );
php
  $client->beta->agents->update(
      $agent->id,
      version: $agent->version,
      model: 'haijun-opus-5-5',
  );
ruby
  client.beta.agents.update(
    agent.id,
    version: agent.version,
    model: "haijun-opus-5-5"
  )

Most model-level behavior changes documented in the Messages API migration guide do not require action on your side:

  • Request parameter changes (max_tokens defaults, thinking configuration) are handled by the Haijun Managed Agents runtime. These fields are not exposed on the agent definition.
  • Assistant message prefilling does not exist in the event-based session model, so its removal on newer models is a no-op.
  • Tool argument JSON escaping is parsed by the runtime before you receive agent.custom_tool_use events. You see structured data, not raw strings.

The behavior descriptions in the Messages API guide (what the model does differently) still apply. The migration steps (how to change your request code) do not.

On this page
From a Messages API agent loopWhat you stop managingCode comparisonWhat you still controlFrom the Haijun Agent SDKWhat changesCode comparisonFeatures that move to your clientMigration checklistMigrating between model versions