--- title: The Mypy Blog: Mypy 2.3 Released | daily.dev description: Mypy 2.3.0 is now available on PyPI, bringing significant memory safety improvements for free-threaded (no-GIL) Python builds compiled with mypyc, including... canonical: https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: The Mypy Blog: Mypy 2.3 Released | daily.dev og:description: Mypy 2.3.0 is now available on PyPI, bringing significant memory safety improvements for free-threaded (no-GIL) Python builds compiled with mypyc, including... og:url: https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7 og:image: https://api.daily.dev/og/posts/RPUcaScF7.png og:image:alt: The Mypy Blog: Mypy 2.3 Released og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # The Mypy Blog: Mypy 2.3 Released **[mypy - Optional Static Typing for Python](https://daily.dev/sources/mypy-lang)** · 4 min read · 0 upvotes · 0 comments ## Summary Mypy 2.3.0 is now available on PyPI, bringing significant memory safety improvements for free-threaded (no-GIL) Python builds compiled with mypyc, including memory-safe list operations, mostly memory-safe instance attribute access, and a new librt.threading.Lock optimized for compiled code that's 2-4x faster than threading.Lock. Final instance attributes are now read-only at runtime for additional optimizations. The team also announced plans to enable the new native parser (--native-parser) by default soon and is asking users to test it. Various bug fixes cover dataclass narrowing regressions, star import dependencies, and typeshed stub updates. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What memory safety improvements does mypy 2.3 add for free-threaded Python builds? Mypy 2.3.0 makes list operations memory-safe on free-threaded (no-GIL) Python builds even under race conditions, and makes instance attribute access mostly memory safe as well, with remaining unsafe cases planned for a future release. These safety guarantees add some performance overhead, so librt.vecs.vec is offered as a faster but not fully memory-safe alternative to list. _Track mypyc's free-threading progress as you evaluate no-GIL Python for production workloads on daily.dev._ ### How much faster is librt.threading.Lock compared to threading.Lock in mypyc? librt.threading.Lock, a new lock type in mypy 2.3 optimized for compiled code, can be 2x to 4x faster than the standard threading.Lock. It was contributed to help developers safely use faster list-like structures such as librt.vecs.vec, which is not inherently memory safe under race conditions. _Compare concurrency primitives like this as you tune performance-critical Python code on daily.dev._ ### What happens when you mark an instance attribute as Final in mypyc compiled code? As of mypy 2.3, instance attributes of native classes declared as Final become read-only at runtime, which enables additional compiler optimizations. It is now recommended to use Final for all performance-sensitive attributes where feasible to take advantage of this. _Follow mypyc optimization changes like this on daily.dev when squeezing performance out of typed Python._ ## Similar posts on daily.dev - [PyCoder’s Weekly](https://daily.dev/posts/pycoder-s-weekly-0wba8c5pq) · Planet Python · 1 upvotes · 0 comments - [Python 3.15 Hits Feature Freeze and Other News for June 2026 – Real Python](https://daily.dev/posts/python-3-15-hits-feature-freeze-and-other-news-for-june-2026-real-python-doxhua30e) · Real Python · 1 upvotes · 0 comments - [What’s up Python? Pip supports locking, .pth files deprecated](https://daily.dev/posts/what-s-up-python-pip-supports-locking-pth-files-deprecated-n4hooa91j) · Bite Code · 3 upvotes · 2 comments --- Tags: [#general-programming](https://daily.dev/tags/general-programming), [#python](https://daily.dev/tags/python) [View this post on daily.dev](https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"The Mypy Blog: Mypy 2.3 Released","url":"https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7"},"datePublished":"2026-08-23T12:17:39.110Z","dateModified":"2026-08-23T12:24:17.846Z","description":"Mypy 2.3.0 is now available on PyPI, bringing significant memory safety improvements for free-threaded (no-GIL) Python builds compiled with mypyc, including...","image":"https://media.daily.dev/image/upload/s--foaA6JGU--/f_auto/v1722860399/public/Placeholder%2004","thumbnailUrl":"https://media.daily.dev/image/upload/s--foaA6JGU--/f_auto/v1722860399/public/Placeholder%2004","isAccessibleForFree":true,"articleSection":"mypy - Optional Static Typing for Python","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"mypy - Optional Static Typing for Python","logo":"https://media.daily.dev/image/upload/logos/placeholder.jpg","url":"https://daily.dev/sources/mypy-lang"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"general-programming,python","timeRequired":"PT4M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"mypy - Optional Static Typing for Python","item":"https://daily.dev/sources/mypy-lang"},{"@type":"ListItem","position":3,"name":"The Mypy Blog: Mypy 2.3 Released"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/the-mypy-blog-mypy-2-3-released-rpucascf7#faq","mainEntity":[{"@type":"Question","name":"What memory safety improvements does mypy 2.3 add for free-threaded Python builds?","acceptedAnswer":{"@type":"Answer","text":"Mypy 2.3.0 makes list operations memory-safe on free-threaded (no-GIL) Python builds even under race conditions, and makes instance attribute access mostly memory safe as well, with remaining unsafe cases planned for a future release. 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