# AN-2026-0855: MCP Python SDK 2.0 (Jul 28, 2026) timeouts take float seconds: a leftover timedelta raises TypeError: unsupported operand type(s) for +: 'float' and 'datetime.timedelta'

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- id: AN-2026-0855 (version 1; cite https://breakwire.org/claim/AN-2026-0855/v/1)
- kind: breaking · status: active · review: editor
- source: <https://py.sdk.modelcontextprotocol.io/v2/migration/#:~:text=Timeouts%20take%20float%20seconds%20instead%20of%20timedelta>
- more sources: <https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0> <https://pypi.org/project/mcp/2.0.0/>
- event date: 2026-07-28
- services: mcp-python-sdk, mcp, python
- affected: pypi:mcp >=2.0.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The v2 migration guide says every timeout parameter that took datetime.timedelta in v1 (ClientSession(read_timeout_seconds=), call_tool(read_timeout_seconds=), send_request(request_read_timeout_seconds=), ClientSessionGroup.call_tool, StreamableHttpParameters.timeout / sse_read_timeout, ServerSession.send_request) now takes float seconds.  [✓0 ✗0]
1. The guide says StreamableHttpParameters fails at construction (ValidationError: Input should be a valid number), while the session-path parameters accept the timedelta and the first request that arms the timeout crashes inside anyio with TypeError: unsupported operand type(s) for +: 'float' and 'datetime.timedelta', an error that never names the parameter.  [✓0 ✗0]

## Fix
```text
Replace `timedelta(seconds=30)` with `30` (or append `.total_seconds()`) in every MCP timeout argument.
```

## Error signatures
- substring: `unsupported operand type(s) for +: 'float' and 'datetime.timedelta'` (v2 migration guide; generic Python/anyio text, scoped to the service)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0855/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28