# Migration Guide: v1 to v2

This guide covers the breaking changes introduced in v2 of the MCP Python SDK and how to update your code.

## Overview

Version 2 of the MCP Python SDK introduces several breaking changes to improve the API, align with the MCP specification, and provide better type safety.

## Breaking Changes

### `streamablehttp_client` removed

The deprecated `streamablehttp_client` function has been removed. Use `streamable_http_client` instead.

**Before (v1):**

```python
from mcp.client.streamable_http import streamablehttp_client

async with streamablehttp_client(
    url="http://localhost:8000/mcp",
    headers={"Authorization": "Bearer token"},
    timeout=30,
    sse_read_timeout=300,
    auth=my_auth,
) as (read_stream, write_stream, get_session_id):
    ...
```

**After (v2):**

```python
import httpx
from mcp.client.streamable_http import streamable_http_client

# Configure headers, timeout, and auth on the httpx.AsyncClient
http_client = httpx.AsyncClient(
    headers={"Authorization": "Bearer token"},
    timeout=httpx.Timeout(30, read=300),
    auth=my_auth,
)

async with http_client:
    async with streamable_http_client(
        url="http://localhost:8000/mcp",
        http_client=http_client,
    ) as (read_stream, write_stream, get_session_id):
        ...
```

### `StreamableHTTPTransport` parameters removed

The `headers`, `timeout`, `sse_read_timeout`, and `auth` parameters have been removed from `StreamableHTTPTransport`. Configure these on the `httpx.AsyncClient` instead (see example above).

### Removed type aliases and classes

The following deprecated type aliases and classes have been removed from `mcp.types`:

| Removed | Replacement |
|---------|-------------|
| `Content` | `ContentBlock` |
| `ResourceReference` | `ResourceTemplateReference` |

**Before (v1):**

```python
from mcp.types import Content, ResourceReference
```

**After (v2):**

```python
from mcp.types import ContentBlock, ResourceTemplateReference
```

### `args` parameter removed from `ClientSessionGroup.call_tool()`

The deprecated `args` parameter has been removed from `ClientSessionGroup.call_tool()`. Use `arguments` instead.

**Before (v1):**

```python
result = await session_group.call_tool("my_tool", args={"key": "value"})
```

**After (v2):**

```python
result = await session_group.call_tool("my_tool", arguments={"key": "value"})
```

### `cursor` parameter removed from `ClientSession` list methods

The deprecated `cursor` parameter has been removed from the following `ClientSession` methods:

- `list_resources()`
- `list_resource_templates()`
- `list_prompts()`
- `list_tools()`

Use `params=PaginatedRequestParams(cursor=...)` instead.

**Before (v1):**

```python
result = await session.list_resources(cursor="next_page_token")
result = await session.list_tools(cursor="next_page_token")
```

**After (v2):**

```python
from mcp.types import PaginatedRequestParams

result = await session.list_resources(params=PaginatedRequestParams(cursor="next_page_token"))
result = await session.list_tools(params=PaginatedRequestParams(cursor="next_page_token"))
```

### `mount_path` parameter removed from FastMCP

The `mount_path` parameter has been removed from `FastMCP.__init__()`, `FastMCP.run()`, `FastMCP.run_sse_async()`, and `FastMCP.sse_app()`. It was also removed from the `Settings` class.

This parameter was redundant because the SSE transport already handles sub-path mounting via ASGI's standard `root_path` mechanism. When using Starlette's `Mount("/path", app=mcp.sse_app())`, Starlette automatically sets `root_path` in the ASGI scope, and the `SseServerTransport` uses this to construct the correct message endpoint path.

### Resource URI type changed from `AnyUrl` to `str`

The `uri` field on resource-related types now uses `str` instead of Pydantic's `AnyUrl`. This aligns with the [MCP specification schema](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/draft/schema.ts) which defines URIs as plain strings (`uri: string`) without strict URL validation. This change allows relative paths like `users/me` that were previously rejected.

**Before (v1):**

```python
from pydantic import AnyUrl
from mcp.types import Resource

# Required wrapping in AnyUrl
resource = Resource(name="test", uri=AnyUrl("users/me"))  # Would fail validation
```

**After (v2):**

```python
from mcp.types import Resource

# Plain strings accepted
resource = Resource(name="test", uri="users/me")  # Works
resource = Resource(name="test", uri="custom://scheme")  # Works
resource = Resource(name="test", uri="https://example.com")  # Works
```

If your code passes `AnyUrl` objects to URI fields, convert them to strings:

```python
# If you have an AnyUrl from elsewhere
uri = str(my_any_url)  # Convert to string
```

Affected types:

- `Resource.uri`
- `ReadResourceRequestParams.uri`
- `ResourceContents.uri` (and subclasses `TextResourceContents`, `BlobResourceContents`)
- `SubscribeRequestParams.uri`
- `UnsubscribeRequestParams.uri`
- `ResourceUpdatedNotificationParams.uri`

The `ClientSession.read_resource()`, `subscribe_resource()`, and `unsubscribe_resource()` methods now accept both `str` and `AnyUrl` for backwards compatibility.

## Deprecations

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## New Features

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## Need Help?

If you encounter issues during migration:

1. Check the [API Reference](api.md) for updated method signatures
2. Review the [examples](https://github.com/modelcontextprotocol/python-sdk/tree/main/examples) for updated usage patterns
3. Open an issue on [GitHub](https://github.com/modelcontextprotocol/python-sdk/issues) if you find a bug or need further assistance