AnyIO
Python async compatibility layer that works with both asyncio and Trio. AnyIO provides a unified async API for networking, file I/O, synchronization primitives, and task groups that runs on either asyncio or Trio backend. Used by FastAPI, HTTPX, and Starlette for async portability. Enables library authors to write async code once that works across multiple async frameworks.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Local async library — no network access or credentials. Security of network operations depends on the code using AnyIO.
⚡ Reliability
Best When
You're writing an async library that should work with both asyncio and Trio, or you want structured concurrency (TaskGroup) patterns portable across backends.
Avoid When
You're building a simple asyncio application that won't need Trio compatibility — use asyncio directly.
Use Cases
- • Write async agent library code that works on both asyncio and Trio without backend-specific code
- • Use structured concurrency (task groups) for managing parallel agent tasks with proper cancellation
- • Build portable async agent utilities (timeouts, cancellation, semaphores) that work across async frameworks
- • Develop FastAPI-integrated agent backends leveraging AnyIO's task group primitives for parallel operations
- • Write async file I/O in agent pipelines with cross-platform async file access
Not For
- • Applications that only use asyncio and don't need Trio compatibility — asyncio directly is simpler
- • Synchronous Python code — AnyIO is for async programming only
- • High-performance network servers where asyncio's raw performance is needed without abstraction overhead
Interface
Authentication
Local Python library — no authentication.
Pricing
Completely free and open source.
Agent Metadata
Known Gotchas
- ⚠ AnyIO 4.x requires Python 3.8+ and uses ExceptionGroup (Python 3.11+) for task group errors — on older Python, install exceptiongroup backport
- ⚠ anyio.create_task_group() is structured concurrency — all tasks in the group must complete before the context manager exits; no fire-and-forget
- ⚠ Backend selection (asyncio vs trio) is at the top-level anyio.run() call — you can't switch backends mid-application
- ⚠ AnyIO's async file operations are slower than sync I/O for small files — use only when blocking I/O would harm event loop responsiveness
- ⚠ When using with FastAPI/Starlette (which use anyio internally), avoid creating nested anyio backends — the framework manages the event loop
- ⚠ CancelScope.deadline is absolute time, not relative — use anyio.move_on_after(seconds) for relative timeouts which is more readable
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for AnyIO.
Scores are editorial opinions as of 2026-03-06.