Claude Agent SDK for Elixir

An Elixir SDK aiming for high parity with the official claude-agent-sdk-python while treating the Claude Code CLI as the authoritative runtime contract. Build AI-powered applications with Claude using a production-ready interface for the Claude Code CLI, featuring streaming responses, lifecycle hooks, permission controls, and in-process tool execution via MCP.

Note: This SDK does not bundle the Claude Code CLI. You must install it separately (see Prerequisites).

Documentation Menu

• README.md - installation, quick start, and ownership boundaries
• guides/getting-started.md - first query and streaming flows
• guides/configuration.md - runtime config and defaults
• guides/model-configuration.md - Claude model selection and effort controls
• guides/agents.md - agent and orchestration patterns
• guides/testing.md - local validation workflow
• guides/provider_behavior_manifest.md - evidence for Claude-native feature translation

What You Can Build

• AI coding assistants with real-time streaming output
• Automated code review pipelines with custom permission policies
• Multi-agent workflows with specialized personas
• Tool-augmented applications using the Model Context Protocol (MCP)
• Interactive chat interfaces with typewriter-style output

Runtime Architecture

• Common CLI query/streaming flows run on the shared cli_subprocess_core runtime: CliSubprocessCore.Session, CliSubprocessCore.RawSession, and CliSubprocessCore.Command.
• ClaudeAgentSDK.Client remains SDK-local only for the advanced Claude control family: hooks, permission callbacks, SDK MCP routing, and control request/response state.
• ClaudeAgentSDK.Client now runs its control lane through CliSubprocessCore.ProtocolSession; custom transport injection has been removed. Use Options.execution_surface for SSH/local routing.

ASM Boundary

If you enter Claude through agent_session_manager, the normalized ASM kernel still stops at provider selection, lane selection, event projection, and session/run orchestration.

The optional ASM seam for Claude lives under ASM.Extensions.ProviderSDK.Claude. That extension may:

• derive ClaudeAgentSDK.Options from ASM-style config
• start ClaudeAgentSDK.Client from ASM session defaults or ASM-style config

If claude_agent_sdk is present in the dependency graph, ASM activates that namespace automatically in ASM.Extensions.ProviderSDK.available_extensions/0 and ASM.Extensions.ProviderSDK.capability_report/0. Client apps do not need to register it manually.

Common fields such as cwd, model, max_turns, and transport timeouts may be derived from ASM config. Claude-native controls such as permission modes, hooks, MCP, settings, agents, tool lists, and system prompt channels must stay in this SDK or be passed through an explicit Claude-native override bag.

It does not move the control family into ASM. Once you cross that seam, the real control APIs remain here:

• ClaudeAgentSDK.Client.set_permission_mode/2
• ClaudeAgentSDK.Client.set_model/2
• ClaudeAgentSDK.Client.interrupt/1
• ClaudeAgentSDK.Client.rewind_files/2
• ClaudeAgentSDK.ControlProtocol.Protocol

SDK-direct live verification lives in examples/promotion_path/sdk_direct_claude.exs. It uses the Claude SDK API without importing ASM, passes keyword execution_surface input, and demonstrates Claude-native tool suppression as SDK-owned behavior:

mix run examples/promotion_path/sdk_direct_claude.exs \
  --model haiku \
  --prompt "Reply with exactly: claude sdk direct ok"

Provider-native feature evidence is tracked in guides/provider_behavior_manifest.md. Add or update that manifest before translating any new Claude-specific CLI flag, control-client behavior, hook, MCP, permission, or settings feature.

Packaging Boundary

Phase 4 finalizes the Claude release boundary:

• cli_subprocess_core remains the required lower dependency for the common Claude query and streaming lane
• claude_agent_sdk remains the source of truth for Claude-native control features such as hooks, permission callbacks, SDK MCP routing, and control protocol state
• ASM may bridge into that richer family only through ASM.Extensions.ProviderSDK.Claude; that seam does not move the control family into ASM or the shared core
• the operator publication order is the two Ground Plane leaves, Execution Plane 0.1.0, cli_subprocess_core 0.2.0, claude_agent_sdk 0.18.0, then agent_session_manager; this SDK does not import Execution Plane directly

Schema Boundary

Zoi is now the canonical boundary-schema layer for new dynamic boundary work inside claude_agent_sdk.

• cli_subprocess_core owns the shared common-lane event and payload shapes.
• claude_agent_sdk owns Claude-local control-protocol envelopes, permission update payloads, and Claude-native message-frame adaptation.
• public structs such as %ClaudeAgentSDK.Message{}, %ClaudeAgentSDK.Permission.Update{}, and %ClaudeAgentSDK.Permission.RuleValue{} remain the ergonomic caller-facing layer.
• forward-compatible wire surfaces use Zoi.map(..., unrecognized_keys: :preserve) plus projection instead of direct Zoi.struct/3.
• closed local payloads still use schema validation, but unknown-field preservation is only enabled where the wire surface can legitimately expand.

Centralized Model Selection

claude_agent_sdk no longer owns active model defaulting or fallback policy. That authority lives in cli_subprocess_core.

Authoritative core surface:

• CliSubprocessCore.ModelRegistry.resolve/3
• CliSubprocessCore.ModelRegistry.validate/2
• CliSubprocessCore.ModelRegistry.default_model/2
• CliSubprocessCore.ModelRegistry.build_arg_payload/3
• CliSubprocessCore.ModelInput.normalize/3

Claude-side behavior:

• ClaudeAgentSDK.Options.new/1 routes mixed raw-versus-payload input through CliSubprocessCore.ModelInput.normalize/3, then ensures model_payload and model are aligned from the shared core contract
• ClaudeAgentSDK.Model.default_model/0 reads the shared core default instead of carrying a local fallback
• effort gating runs against the resolved model, not mutable app config
• provider CLI rendering only formats arguments from resolved values
• repo-local env defaults remain fallback inputs only when model_payload was not supplied explicitly

Do not treat repo-local config snapshots as authoritative model policy. The shared core registry is the source of truth.

Claude Ollama Backend

claude_agent_sdk now supports an explicit Claude :ollama backend through the same core-owned payload path.

Example:

options =
  ClaudeAgentSDK.Options.new(
    provider_backend: :ollama,
    anthropic_base_url: "http://localhost:11434",
    external_model_overrides: %{"haiku" => "llama3.2"},
    model: "haiku"
  )

The SDK still runs the normal claude binary. The core payload resolves the actual transport model and injects the Anthropic-compatible Ollama env.

Installation

Claude Agent SDK 0.18 requires Elixir 1.19 or later.

Add to your mix.exs:

def deps do
  [
    {:claude_agent_sdk, "~> 0.18.0"}
  ]
end

Then fetch dependencies:

mix deps.get

Prerequisites

Install the Claude Code CLI (requires Node.js):

npm install -g @anthropic-ai/claude-code

Verify installation:

claude --version

CLI Compatibility

• Minimum supported Claude CLI version: 2.1.0
• Recommended Claude CLI version: 2.1.207
• Parity baseline: Python SDK v0.2.116 / TypeScript SDK v0.3.207 (CLI 2.1.207), including the 2.1.203–2.1.207 protocol frames — terminal_reason (Message.dead_turn?/1), background_tasks_changed (Message.live_background_tasks/1), command_lifecycle (Message.command_terminal?/1), typed interrupt receipts with still_queued, system/init capabilities (Message.capability?/2), peer-message origin (Message.peer_origin/1), and AgentToolCompletedOutput (Message.agent_tool_completed/1).
• Compatibility policy: this SDK follows the Python SDK where practical, but the Claude CLI wire protocol is authoritative. CLI-native frames such as :rate_limit_event are surfaced here even if the current Python SDK skips unknown message types for forward compatibility.

Quick Start

1. Authenticate

Choose one method:

# Option A: Environment variable (recommended for CI/CD)
export ANTHROPIC_API_KEY="sk-ant-api03-..."

# Option B: OAuth token
export CLAUDE_AGENT_OAUTH_TOKEN="sk-ant-oat01-..."

# Option C: Interactive login
claude login

2. Run Your First Query

alias ClaudeAgentSDK.{ContentExtractor, Options}

# Simple query with streaming collection
ClaudeAgentSDK.query("Write a function that calculates factorial in Elixir")
|> Enum.each(fn msg ->
  case msg.type do
    :assistant -> IO.puts(ContentExtractor.extract_text(msg) || "")
    :result -> IO.puts("Done! Cost: $#{msg.data.total_cost_usd}")
    _ -> :ok
  end
end)

3. Real-Time Streaming

alias ClaudeAgentSDK.Streaming

{:ok, session} = Streaming.start_session()

Streaming.send_message(session, "Explain GenServers in one paragraph")
|> Stream.each(fn
  %{type: :text_delta, text: chunk} -> IO.write(chunk)
  %{type: :message_stop} -> IO.puts("")
  _ -> :ok
end)
|> Stream.run()

Streaming.close_session(session)

If session initialization or message send fails, the stream now emits an immediate %{type: :error, error: reason} event instead of waiting for the 5-minute stream timeout.

Authentication

The SDK supports three authentication methods, checked in this order:

These methods are standalone compatibility paths for direct SDK use. Governed launch callers must pass Options.governed_authority with the materialized command, cwd, environment, auth/config roots, target reference, credential lease reference, command reference, and redaction reference. In governed mode, ambient env values, native login state, provider backend overrides, token-store defaults, and explicit CLI paths are rejected instead of being used as fallback authentication.

AuthManager.get_token/1 does not project raw credentials for governed authority. It reports {:error, :governed_token_unavailable} so upper layers carry only authority and lease references.

Cloud Providers

AWS Bedrock:

export CLAUDE_AGENT_USE_BEDROCK=1
export AWS_ACCESS_KEY_ID=...
export AWS_SECRET_ACCESS_KEY=...
export AWS_REGION=us-west-2

Google Vertex AI:

export CLAUDE_AGENT_USE_VERTEX=1
export GOOGLE_APPLICATION_CREDENTIALS=/path/to/key.json
export GOOGLE_CLOUD_PROJECT=your-project-id

Token Setup (Local Development)

For persistent authentication without re-login:

mix claude.setup_token

AuthManager keeps running if token storage save/clear fails and returns {:error, reason}. Handle clear_auth/0 accordingly in your app code:

case ClaudeAgentSDK.AuthManager.clear_auth() do
  :ok -> :ok
  {:error, reason} -> IO.puts("Failed to clear auth: #{inspect(reason)}")
end

Check authentication status:

alias ClaudeAgentSDK.AuthChecker
diagnosis = AuthChecker.diagnose()
# => %{authenticated: true, auth_method: "Anthropic API", ...}

Core Concepts

Choosing the Right API

Query API

The simplest way to interact with Claude:

# Basic query
messages = ClaudeAgentSDK.query("What is recursion?") |> Enum.to_list()

# With options
opts = %ClaudeAgentSDK.Options{
  model: "sonnet",
  max_turns: 5,
  output_format: :stream_json
}
messages = ClaudeAgentSDK.query("Explain OTP", opts) |> Enum.to_list()

# Streamed input prompts (unidirectional)
prompts = [
  %{"type" => "user", "message" => %{"role" => "user", "content" => "Hello"}},
  %{"type" => "user", "message" => %{"role" => "user", "content" => "How are you?"}}
]

ClaudeAgentSDK.query(prompts, opts) |> Enum.to_list()

# Execution-surface routing
opts = %ClaudeAgentSDK.Options{
  execution_surface: [
    surface_kind: :ssh_exec,
    transport_options: [
      destination: "claude.example",
      ssh_user: "sdk",
      port: 22
    ]
  ]
}

ClaudeAgentSDK.query("Hello", opts) |> Enum.to_list()

# Continue a conversation
ClaudeAgentSDK.continue("Can you give an example?") |> Enum.to_list()

# Resume a specific session
ClaudeAgentSDK.resume("session-id", "What about supervision trees?") |> Enum.to_list()

Streaming API

For real-time, character-by-character output:

alias ClaudeAgentSDK.{Options, Streaming}

{:ok, session} = Streaming.start_session(%Options{model: "haiku"})

# Send messages and stream responses
Streaming.send_message(session, "Write a haiku about Elixir")
|> Enum.each(fn
  %{type: :text_delta, text: t} -> IO.write(t)
  %{type: :tool_use_start, name: n} -> IO.puts("\nUsing tool: #{n}")
  %{type: :message_stop} -> IO.puts("\n---")
  _ -> :ok
end)

# Multi-turn conversation (context preserved)
Streaming.send_message(session, "Now write one about Phoenix")
|> Enum.to_list()

Streaming.close_session(session)

Subagent Streaming: When Claude spawns subagents via the Agent tool, events include a parent_tool_use_id field to identify the source. Main agent events have nil, subagent events have the Agent tool call ID. Streaming events also preserve uuid, session_id, and raw_event metadata when the CLI provides them. See the Streaming Guide for details.

Hooks System

Intercept and control agent behavior at key lifecycle points:

alias ClaudeAgentSDK.{Client, Options}
alias ClaudeAgentSDK.Hooks.{Matcher, Output}

# Block dangerous commands
check_bash = fn input, _id, _ctx ->
  case input do
    %{"tool_name" => "Bash", "tool_input" => %{"command" => cmd}} ->
      if String.contains?(cmd, "rm -rf") do
        Output.deny("Dangerous command blocked")
      else
        Output.allow()
      end
    _ -> %{}
  end
end

opts = %Options{
  hooks: %{
    pre_tool_use: [Matcher.new("Bash", [check_bash])]
  }
}

{:ok, client} = Client.start_link(opts)

Available Hook Events (all 12 Python SDK events supported):

• pre_tool_use / post_tool_use / post_tool_use_failure - Tool execution lifecycle
• user_prompt_submit - Before sending user messages
• stop / subagent_stop / subagent_start - Agent lifecycle
• notification - CLI notifications
• permission_request - Permission dialog interception
• session_start / session_end - Session lifecycle
• pre_compact - Before context compaction

See the Hooks Guide for comprehensive documentation.

Supervision

Hook and permission callbacks run in async tasks. For production, add the SDK task supervisor so callback processes are supervised:

children = [
  ClaudeAgentSDK.TaskSupervisor,
  {ClaudeAgentSDK.Client, options}
]

If you use a custom supervisor name, configure the SDK to match:

children = [
  {ClaudeAgentSDK.TaskSupervisor, name: MyApp.ClaudeTaskSupervisor}
]

config :claude_agent_sdk, task_supervisor: MyApp.ClaudeTaskSupervisor

If an explicitly configured supervisor is missing at runtime, the SDK logs a warning and falls back to Task.start/1. With default settings, missing ClaudeAgentSDK.TaskSupervisor falls back silently for backward compatibility. For stricter behavior in dev/test:

config :claude_agent_sdk, task_supervisor_strict: true

In strict mode, ClaudeAgentSDK.TaskSupervisor.start_child/2 returns {:error, {:task_supervisor_unavailable, supervisor}} instead of spawning an unsupervised fallback task.

Permission System

Fine-grained control over tool execution:

alias ClaudeAgentSDK.{Options, Permission.Result}

permission_callback = fn ctx ->
  case ctx.tool_name do
    "Write" ->
      # Redirect system file writes to safe location
      if String.starts_with?(ctx.tool_input["file_path"], "/etc/") do
        safe_path = "/tmp/sandbox/" <> Path.basename(ctx.tool_input["file_path"])
        Result.allow(updated_input: %{ctx.tool_input | "file_path" => safe_path})
      else
        Result.allow()
      end
    _ ->
      Result.allow()
  end
end

opts = %Options{
  can_use_tool: permission_callback,
  permission_mode: :default  # :default | :accept_edits | :plan | :bypass_permissions | :auto | :dont_ask
}

Note: can_use_tool is mutually exclusive with permission_prompt_tool. The SDK routes can_use_tool through the control client (including string prompts), auto-enables include_partial_messages, and sets permission_prompt_tool to \"stdio\" internally so the CLI can emit permission callbacks. Use :default, :plan, or the CLI's :auto mode for built-in tool permissions. Hook-based fallback only applies when the CLI does not emit can_use_tool, and that fallback ignores updated_permissions. :delegate is no longer forwarded because current Claude CLI builds reject it.

CLI transcript history now matches the official SDK surface:

# Claude CLI transcript history
sessions = ClaudeAgentSDK.list_sessions(directory: "/path/to/project")
messages = ClaudeAgentSDK.get_session_messages("550e8400-e29b-41d4-a716-446655440000",
  directory: "/path/to/project"
)

# SDK-managed SessionStore history
{:ok, saved_sessions} = ClaudeAgentSDK.list_saved_sessions(storage_dir: "/custom/path")

# Official SessionStore adapter surface
store = ClaudeAgentSDK.SessionStore.InMemory.new!()
session_id = "550e8400-e29b-41d4-a716-446655440000"
project_key = ClaudeAgentSDK.project_key_for_directory("/path/to/project")

:ok =
  ClaudeAgentSDK.SessionStore.Adapter.append(store, %{project_key: project_key, session_id: session_id}, [
    %{"type" => "user", "uuid" => "u1", "sessionId" => session_id, "message" => %{"content" => "hello"}}
  ])

sessions = ClaudeAgentSDK.list_sessions_from_store(store, directory: "/path/to/project")
messages = ClaudeAgentSDK.get_session_messages_from_store(session_id, store,
  directory: "/path/to/project"
)

Stream a single client response until the final result:

Client.receive_response_stream(client)
|> Enum.to_list()

MCP Tools (In-Process)

Define custom tools that Claude can call directly in your application:

defmodule MyTools do
  use ClaudeAgentSDK.Tool

  deftool :calculate, "Perform a calculation", %{
    type: "object",
    properties: %{
      expression: %{type: "string", description: "Math expression to evaluate"}
    },
    required: ["expression"]
  } do
    def execute(%{"expression" => expr}) do
      # Your logic here
      result = eval_expression(expr)
      {:ok, %{"content" => [%{"type" => "text", "text" => "Result: #{result}"}]}}
    end
  end
end

# Create an MCP server with your tools
server = ClaudeAgentSDK.create_sdk_mcp_server(
  name: "calculator",
  version: "1.0.0",
  tools: [MyTools.Calculate]
)

# Without :supervisor, the SDK keeps the registry under its internal
# SDK MCP supervisor so the server survives creator process exits.

# Optional: start tool registry under your DynamicSupervisor
{:ok, sup} = DynamicSupervisor.start_link(strategy: :one_for_one)

server = ClaudeAgentSDK.create_sdk_mcp_server(
  name: "calculator",
  version: "1.0.0",
  tools: [MyTools.Calculate],
  supervisor: sup
)

opts = %ClaudeAgentSDK.Options{
  mcp_servers: %{"calc" => server},
  allowed_tools: ["mcp__calc__calculate"]
}

Note: MCP server routing only supports initialize, tools/list, tools/call, and notifications/initialized. Calls to resources/list or prompts/list return JSON-RPC method-not-found errors to match the Python SDK. If version is omitted, it defaults to "1.0.0".

Configuration Options

Key options for ClaudeAgentSDK.Options:

CLI path override: set path_to_claude_code_executable or executable in Options (Python cli_path equivalent).

On SSH-backed execution_surface values, Claude is resolved on the remote host. If the binary is installed outside the remote non-login PATH, pass an explicit executable or path_to_claude_code_executable for that target.

Runtime Application Config

All tunable constants (timeouts, buffer sizes, auth paths, CLI flags, env var names, concurrency limits) are centralized in Config.* sub-modules and can be overridden per-environment:

# config/config.exs
config :claude_agent_sdk, ClaudeAgentSDK.Config.Timeouts,
  query_total_ms: 5_400_000,           # total query timeout (default: 75 min)
  tool_execution_ms: 60_000            # per-tool timeout (default: 30 s)

config :claude_agent_sdk, ClaudeAgentSDK.Config.Buffers,
  max_stdout_buffer_bytes: 2_097_152   # stdout buffer (default: 1 MB)

config :claude_agent_sdk, ClaudeAgentSDK.Config.Orchestration,
  max_concurrent: 10,                  # parallel query limit (default: 5)
  max_retries: 5                       # retry attempts (default: 3)

# Legacy flat keys still work:
config :claude_agent_sdk,
  cli_stream_module: ClaudeAgentSDK.Query.CLIStream,
  task_supervisor_strict: false

See the Configuration Internals guide for the complete reference of every tunable, its default, and override examples.

config :claude_agent_sdk, :process_module is still read as a fallback for query streaming, but it is deprecated and logs a warning once per legacy module.

SessionStore now hydrates on-disk cache in a handle_continue/2 step. Startup is faster, but list/search can be briefly incomplete immediately after boot while warmup finishes.

CliSubprocessCore.RawSession and Streaming.Session support startup_mode: :lazy to defer subprocess startup to handle_continue/2. Deterministic startup validation still happens before start_link returns, so missing cwd/command style failures surface immediately. Once preflight passes, lazy mode can still surface subprocess launch failures as a process exit after init.

Query-side transport errors normalize equivalent reasons to stable atoms where possible: {:command_not_found, "claude"} is treated as :cli_not_found.

SDK Logging

The SDK uses its own log level filter (default: :warning) to keep output quiet in dev. Configure via application env:

config :claude_agent_sdk, log_level: :warning  # :debug | :info | :warning | :error | :off

Option Presets

alias ClaudeAgentSDK.OptionBuilder

# Environment-based presets
OptionBuilder.build_development_options()  # Permissive, verbose
OptionBuilder.build_production_options()   # Restrictive, safe
OptionBuilder.for_environment()            # Auto-detect from Mix.env()

# Use-case presets
OptionBuilder.build_analysis_options()     # Read-only code analysis
OptionBuilder.build_chat_options()         # Simple chat, no tools
OptionBuilder.quick()                      # Fast one-off queries

# Effort and thinking helpers
OptionBuilder.with_opus()
|> OptionBuilder.with_effort(:max)
|> OptionBuilder.with_thinking(%{type: :adaptive})

Examples

The examples/ directory contains runnable demonstrations.

Mix Task Example (Start Here)

If you want to integrate Claude into your own Mix project, see the mix_task_chat example — a complete working app with Mix tasks:

cd examples/mix_task_chat
mix deps.get
mix chat "Hello, Claude!"           # Streaming response
mix chat --interactive              # Multi-turn conversation
mix ask -q "What is 2+2?"           # Script-friendly output

Script Examples

# Run all examples
bash examples/run_all.sh

# Run a specific example
mix run examples/basic_example.exs
mix run examples/streaming_tools/quick_demo.exs
mix run examples/hooks/basic_bash_blocking.exs

Key Examples:

• mix_task_chat/ - Full Mix task integration (streaming + interactive chat)
• basic_example.exs - Minimal SDK usage
• streaming_tools/quick_demo.exs - Real-time streaming
• hooks/complete_workflow.exs - Full hooks integration
• sdk_mcp_tools_live.exs - Custom MCP tools
• max_effort_opus_live.exs - Opus :max effort (not in run_all.sh)
• advanced_features/agents_live.exs - Multi-agent workflows
• advanced_features/subagent_spawning_live.exs - Parallel subagent coordination
• advanced_features/web_tools_live.exs - WebSearch and WebFetch

Full Application Examples

Complete Mix applications demonstrating production-ready SDK integration patterns:

# Run Phoenix Chat
cd examples/phoenix_chat && mix deps.get && mix phx.server
# Visit http://localhost:4000

# Run Document Generation
cd examples/document_generation && mix deps.get && mix generate.demo

# Run Research Agent
cd examples/research_agent && mix deps.get && mix research "quantum computing"

# Run Skill Invocation demo
cd examples/skill_invocation && mix deps.get && mix run -e "SkillInvocation.demo()"

# Run Email Agent
cd examples/email_agent && mix deps.get && mix email.assistant "find emails from last week"

Guides

Upgrading

For breaking changes and migration notes, see CHANGELOG.md.

0.12.0 breaking changes:

• Transport.Port removed. The built-in common transport lane now runs through CliSubprocessCore.Command, CliSubprocessCore.RawSession, and CliSubprocessCore.Session.
• Custom transport injection removed from Client, Query, and common CLI lanes. Use Options.execution_surface for SSH/local routing instead.
• Transport error tuple shape updated: low-level failures now use {:error, {:transport, reason}} instead of bare {:error, reason}.
• String prompts now delivered via stdin (--input-format stream-json) instead of CLI arg (-- prompt).

0.11.0 breaking changes:

• --print flag removed from all modules. All queries now use --output-format stream-json exclusively.
• --agents CLI flag removed. Agents are now sent via the initialize control request. Use Options.agents_for_initialize/1.
• AgentsFile module deleted. Remove any agents_temp_file_max_age_seconds config.
• Client state is now a defstruct. Four deprecated fields removed: current_model, pending_model_change, current_permission_mode, pending_inbound_count.
• All 12 hook events are now supported (6 new: post_tool_use_failure, notification, subagent_start, permission_request, session_start, session_end).

0.10.0 fix (resume turn persistence):

• resume/3 no longer uses --print --resume (one-shot mode that dropped intermediate turns). It now uses --resume with --input-format stream-json, preserving the full conversation history across resume calls.
• Current model defaults and aliases are owned by cli_subprocess_core; the native Claude default is sonnet (Claude Sonnet 5). Aliases: opus → Claude Opus 4.8, fable → Claude Fable 5, haiku → Claude Haiku 4.5. A model id newer than the registry passes through to --model verbatim unless allow_unknown_model: false.

0.9.0 breaking change (streaming):

• Stream event wrappers now require uuid and session_id. Missing keys raise and terminate the streaming client.
• If you emit or mock stream_event wrappers, include both fields (custom transports, fixtures, tests).

That strict requirement applies to the common CLI streaming parser. The SDK-local control lane still accepts incomplete stream_event wrappers and surfaces missing metadata as nil, which keeps control-client transports forward-compatible without weakening the core streaming contract.

Additional Resources:

• CHANGELOG.md - Version history and release notes
• HexDocs - API documentation
• Claude Code SDK - Upstream documentation

License

MIT License - see LICENSE for details.

Model Selection Contract

/home/home/p/g/n/claude_agent_sdk no longer owns active model-selection policy. Model catalog visibility, defaulting, validation, and failure semantics are owned by /home/home/p/g/n/cli_subprocess_core through CliSubprocessCore.ModelRegistry.resolve/3, CliSubprocessCore.ModelRegistry.validate/2, and CliSubprocessCore.ModelRegistry.default_model/2.

The Claude SDK now treats model values as resolved payload data and limits its responsibility to option shaping and command rendering.

Session History And Intervention

The Claude runtime lane now publishes an honest session-control contract for orchestration layers.

• ClaudeAgentSDK.Runtime.CLI.capabilities/0 includes :session_history, :session_resume, :session_pause, and :session_intervene
• ClaudeAgentSDK.Runtime.CLI.list_provider_sessions/1 standardizes transcript-history entries for upper layers without flattening the richer native Claude session model

This is meant for recovery and operator-control flows, not blind retries. The caller should resume the same session when possible and only replay work when a real continuation handle is unavailable.