3.5

3.5.0 - 🎃 The Exorcism of Python 3.9 👻

Released on October 31, 2025

With the removal of Python 3.9 support, Prefect now requires Python 3.10 or later. This means you can finally say goodbye to from __future__ import annotations in your workflow code—native type annotations are now standard! This release also removes several long-deprecated features including Runner functionality and system Blocks. Check the Breaking Changes section below for details.

Enhancements ➕➕

• Add on_running hook support for tasks by @zzstoatzz in #19277
• Allow using Field descriptions directly in Flow parameters (#13912) by @jmesterh in #19281
• Add PREFECT_SERVER_UI_SHOW_PROMOTIONAL_CONTENT setting by @zzstoatzz in #19299

Breaking Changes ⚠️

• Remove Python 3.9 support by @desertaxle in #19273
• Remove deprecated Runner functionality and system Blocks by @desertaxle in #19307

Bug Fixes 🐞

• Fix forward reference resolution in ValidatedFunction by @desertaxle in #19289
• Fix datetime parameter serialization in run_deployment by @zzstoatzz in #19278
• Fix time zone normalization bug in interval schedules by @zzstoatzz in #19301
• Fix multiprocessing deadlock after using prefect_test_harness on Linux by @zzstoatzz in #19116

Development & Tidiness 🧹

• Update typer minimum to 0.16.0 for click>=8.2 compatibility by @zzstoatzz in #19269
• Remove weird language by @zzstoatzz in #19271
• Update just recipes to use 3.10 for lowest python by @zzstoatzz in #19297
• Fix duration in generate_deprecation_message by @desertaxle in #19314
• Fix RRuleSchedule test flakiness from DST-dependent date by @zzstoatzz in #19305
• Add debug log for fork handler registration failure by @zzstoatzz in #19311

Documentation 📓

• Add global concurrency limits concept doc and refactor how-to guide by @desertaxle in #19231

Full Changelog: https://github.com/PrefectHQ/prefect/compare/3.4.25…3.5.0

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