Pydantic's Monty ships v1.0.0, dropping the experimental label on its Rust-built Python sandbox for agent code

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pydantic/monty published v1.0.0 on 2026-09-25 (8,323 stars). The release drops the experimental framing and adds percent formatting, the format() builtin, CWD support, eager awaits, long-int handling across pow/round/math, and Python 3.14t wheels. Pydantic's own docs say the filesystem, environment and network do not exist inside the interpreter unless you pass in functions or mounts, and put startup under 1 ms from a running pool against about 1,500 ms for a sandbox service. That makes it a stable option for code-mode agents that write Python instead of making chains of tool calls.