vercel-ai-sdk 0.0.1.dev4

The AI Toolkit for Python

vercel-ai-sdk

A Python version of the AI SDK.

Quick Start

uv add vercel-ai-sdk

import os
import vercel_ai_sdk as ai

@ai.tool
async def talk_to_mothership(question: str) -> str:
    """Contact the mothership for important decisions."""
    return "Soon."

async def agent(llm, query):
    return await ai.stream_loop(
        llm,
        messages=ai.make_messages(
            system="You are a robot assistant.",
            user=query,
        ),
        tools=[talk_to_mothership],
    )

llm = ai.openai.OpenAIModel(
    model="anthropic/claude-opus-4.6",
    base_url="https://ai-gateway.vercel.sh/v1",
    api_key=os.environ["AI_GATEWAY_API_KEY"],
)

async for msg in ai.run(agent, llm, "When will the robots take over?"):
    print(msg.text_delta, end="")

Reference

Core Primitives

ai.run(root, *args, checkpoint=None, cancel_on_hooks=False)

Entry point. Starts root as a background task, processes the step/hook queue, yields Message objects. Returns a RunResult.

result = ai.run(my_agent, llm, "hello")
async for msg in result:
    print(msg.text_delta, end="")

result.checkpoint      # Checkpoint with all completed work
result.pending_hooks   # dict of unresolved hooks (empty if run completed)

If root declares a runtime: ai.Runtime parameter, it's auto-injected.

@ai.tool

Decorator that turns an async function into a Tool. Parameters extracted from type hints, docstring becomes description.

@ai.tool
async def search(query: str, limit: int = 10) -> list[str]:
    """Search the database."""
    ...

If a tool declares a runtime: ai.Runtime parameter, it's auto-injected (not passed by the LLM):

@ai.tool
async def long_task(input: str, runtime: ai.Runtime) -> str:
    """Runtime is auto-injected, not passed by LLM."""
    await runtime.put_message(ai.Message(...))  # stream intermediate results
    ...

@ai.stream

Decorator that wires an async generator into the Runtime. Use this to make any streaming operation (like an LLM call) work with ai.run().

@ai.stream
async def my_custom_step(llm, messages):
    async for msg in llm.stream(messages):
        yield msg

result = await my_custom_step(llm, messages)  # returns StreamResult

Must be called within ai.run() (needs a Runtime context).

@ai.hook

Decorator that creates a suspension point from a pydantic model. The model defines the resolution schema.

@ai.hook
class Approval(pydantic.BaseModel):
    granted: bool
    reason: str

Inside your agent — blocks until resolved:

approval = await Approval.create("approve_send_email", metadata={"tool": "send_email"})
if approval.granted:
    ...

From outside (API handler, websocket, iterator loop, etc.):

Approval.resolve("approve_send_email", {"granted": True, "reason": "User approved"})
Approval.cancel("approve_send_email")  # or cancel it

Long-running mode (cancel_on_hooks=False, the default): the await in create() blocks until resolve() or cancel() is called from external code.

Serverless mode (cancel_on_hooks=True): if no resolution is available, the hook's future is cancelled and the branch dies. Inspect result.pending_hooks and result.checkpoint to resume later:

result = ai.run(my_agent, llm, query, cancel_on_hooks=True)
async for msg in result:
    ...

if result.pending_hooks:
    # Save result.checkpoint, collect resolutions, then re-enter:
    Approval.resolve("approve_send_email", {"granted": True, "reason": "User approved"})
    result = ai.run(my_agent, llm, query, checkpoint=result.checkpoint)
    async for msg in result:
        ...

Convenience Functions

ai.stream_step(llm, messages, tools=None, label=None)

Single LLM call. Built on @ai.stream. Returns StreamResult.

result = await ai.stream_step(llm, messages, tools=[search])
# result.text, result.tool_calls, result.last_message

ai.stream_loop(llm, messages, tools, label=None)

Full agent loop: calls LLM, executes tools, repeats until no more tool calls. Returns final StreamResult.

result = await ai.stream_loop(llm, messages, tools=[search, get_weather])

ai.execute_tool(tool_call, message=None)

Execute a single tool call. Looks up the tool from the global registry (populated by @ai.tool). Updates the ToolPart with the result. If message is provided, emits it to the Runtime queue so the UI sees the status change.

await asyncio.gather(*(ai.execute_tool(tc, message=last_msg) for tc in result.tool_calls))

Supports checkpoint replay — returns the cached result without re-executing if one exists.

ai.make_messages(*, system=None, user)

Build a message list from system + user strings.

messages = ai.make_messages(system="You are helpful.", user="Hello!")

ai.get_checkpoint()

Get the current Checkpoint from the active Runtime context. Call this from within ai.run().

checkpoint = ai.get_checkpoint()

Checkpoints

Checkpoint records completed work (LLM steps, tool executions, hook resolutions) so a run can be replayed without re-executing already-finished operations.

# After a run completes or suspends
checkpoint = result.checkpoint
data = checkpoint.serialize()   # dict, JSON-safe

# Later: restore and resume
checkpoint = ai.Checkpoint.deserialize(data)
result = ai.run(my_agent, llm, query, checkpoint=checkpoint)

Three event types are tracked:

• Steps — LLM call results (replayed without calling the model)
• Tools — tool execution results (replayed without re-executing)
• Hooks — hook resolutions (replayed without re-suspending)

Adapters

LLM Providers

# OpenAI-compatible (including Vercel AI Gateway)
llm = ai.openai.OpenAIModel(
    model="anthropic/claude-opus-4.6",
    base_url="https://ai-gateway.vercel.sh/v1",
    api_key=os.environ["AI_GATEWAY_API_KEY"],
    thinking=True,           # enable reasoning output
    budget_tokens=10000,     # or reasoning_effort="medium"
)

# Anthropic (native client)
llm = ai.anthropic.AnthropicModel(
    model="claude-opus-4.6-20250916",
    thinking=True,
    budget_tokens=10000,
)

MCP

# HTTP transport
tools = await ai.mcp.get_http_tools(
    "https://mcp.example.com/mcp",
    headers={"Authorization": "Bearer ..."},
    tool_prefix="docs",
)

# Stdio transport (subprocess)
tools = await ai.mcp.get_stdio_tools(
    "npx", "-y", "@anthropic/mcp-server-filesystem", "/tmp",
    tool_prefix="fs",
)

MCP connections are pooled per ai.run() and cleaned up automatically.

AI SDK UI

For streaming to AI SDK frontend (useChat, etc.):

from vercel_ai_sdk.ai_sdk_ui import to_sse_stream, to_messages, UI_MESSAGE_STREAM_HEADERS

# Convert incoming UI messages
messages = to_messages(request.messages)

# Stream response as SSE
async def stream_response():
    async for chunk in to_sse_stream(ai.run(agent, llm, query)):
        yield chunk

return StreamingResponse(stream_response(), headers=UI_MESSAGE_STREAM_HEADERS)

Types

Type	Description
Message	Universal message with role, parts, label. Properties: text, text_delta, reasoning_delta, tool_deltas, tool_calls, is_done
TextPart	Text content with streaming state and delta
ToolPart	Tool call with tool_call_id, tool_name, tool_args, status, result. Has .set_result()
ToolDelta	Tool argument streaming delta (tool_call_id, tool_name, args_delta)
ReasoningPart	Model reasoning/thinking with optional signature (Anthropic)
HookPart	Hook suspension with hook_id, hook_type, status (pending/resolved/cancelled), metadata, resolution
Part	Union: TextPart | ToolPart | ReasoningPart | HookPart
PartState	Literal: "streaming" | "done"
StreamResult	Result of a stream step: messages, tool_calls, text, last_message
Tool	Tool definition: name, description, schema, fn
ToolSchema	Serializable tool description: name, description, tool_schema (no fn)
Runtime	Central coordinator for the agent loop. Step queue, message queue, checkpoint replay/record
RunResult	Return type of run(). Async-iterable for messages, then .checkpoint and .pending_hooks
HookInfo	Pending hook info: label, hook_type, metadata
Hook	Generic hook base with .create(), .resolve(), .cancel() class methods
Checkpoint	Serializable snapshot of completed work: steps[], tools[], hooks[]. Has .serialize() / .deserialize()
LanguageModel	Abstract base class for LLM providers

Examples

See the examples/ directory:

Samples (examples/samples/):

• simple.py — Basic agent with tools and stream_loop
• agent.py — Coding agent with local filesystem tools
• hooks.py — Human-in-the-loop approval flow
• streaming_tool.py — Tool that streams progress via Runtime
• multiagent.py — Parallel agents with labels, then summarization
• custom_loop.py — Custom step with @ai.stream
• mcp.py — MCP integration (Context7)

Projects:

• examples/fastapi-vite/ — Full-stack chat app (FastAPI + Vite + AI SDK UI)
• examples/temporal-durable/ — Durable execution with Temporal workflows
• examples/multiagent-textual/ — Multi-agent TUI with Textual