Claude Agent SDK 0.2.140 adds MCP 2.x support and a tool-use permission callback

The Python Claude Agent SDK shipped v0.2.140 on 18 August 2026 carrying four substantive additions: MCP 2.x support, a forward_subagent_text option that surfaces a subagent’s output to the caller, a structured ResultError exception, and support for a can_use_tool callback so the host can decide per invocation whether a tool call is allowed. Three further releases followed in two days — v0.2.141 on 19 August and v0.2.142 on 20 August — each bundling a newer Claude CLI (2.1.236 and 2.1.237 respectively), on top of v0.2.139 on 14 August.

What it means can_use_tool is the hook a host needs to put a real policy in front of an agent’s tool calls instead of trusting the prompt, and MCP 2.x support is the compatibility line anyone pinning an SDK version now has to check.