Ruby 3.3.0-preview3 Released

We are pleased to announce the release of Ruby 3.3.0-preview3. Ruby 3.3 adds a new parser named Prism, uses Lrama as a parser generator, adds a new pure-Ruby JIT compiler named RJIT, and many performance improvements especially YJIT.


  • Introduced the Prism parser as a default gem
    • Prism is a portable, error tolerant, and maintainable recursive descent parser for the Ruby language
  • Prism is production ready and actively maintained, you can use it in place of Ripper
    • There is extensive documentation on how to use Prism
    • Prism is both a C library that will be used internally by CRuby and a Ruby gem that can be used by any tooling which needs to parse Ruby code
    • Notable methods in the Prism API are:
      • Prism.parse(source) which returns the AST as part of a ParseResult
      • Prism.dump(source) which returns the serialized AST as a String
      • Prism.parse_comments(source) which returns the comments
  • You can make pull requests or issues directly on the Prism repository if you are interested in contributing

Use Lrama instead of Bison


  • Introduced a pure-Ruby JIT compiler RJIT and replaced MJIT.
    • RJIT supports only x86-64 architecture on Unix platforms.
    • Unlike MJIT, it doesn’t require a C compiler at runtime.
  • RJIT exists only for experimental purposes.
    • You should keep using YJIT in production.
  • If you are interested in developing JIT for Ruby, please check out k0kubun’s presentation on Day 3 of RubyKaigi.


  • Major performance improvements over 3.2
    • Support for splat and rest arguments has been improved.
    • Registers are allocated for stack operations of the virtual machine.
    • More calls with optional arguments are compiled.
    • Exception handlers are also compiled.
    • Instance variables no longer exit to the interpreter with megamorphic object shapes.
    • Unsupported call types no longer exit to the interpreter.
    • Integer#!=, String#!=, Kernel#block_given?, Kernel#is_a?, Kernel#instance_of?, Module#=== are specially optimized.
    • Now more than 3x faster than the interpreter on optcarrot!
  • Significantly improved memory usage over 3.2
    • Metadata for compiled code uses a lot less memory.
    • Generate more compact code on ARM64
  • Compilation speed is now slightly faster than 3.2.
  • Add RubyVM::YJIT.enable that can enable YJIT at run-time
    • You can start YJIT without modifying command-line arguments or environment variables.
    • This can also be used to enable YJIT only once your application is done booting. --yjit-disable can be used if you want to use other YJIT options while disabling YJIT at boot.
  • Option to disable code GC and treat --yjit-exec-mem-size as a hard limit
    • Can produce better copy-on-write behavior on servers using unicorn and forking
  • ratio_in_yjit stat produced by --yjit-stats is now available in release builds, a special stats or dev build is no longer required to access most stats.
  • Exit tracing option now supports sampling
    • --trace-exits-sample-rate=N
  • --yjit-perf is added to facilitate profiling with Linux perf.
  • More thorough testing and multiple bug fixes

M:N thread scheduler

  • M:N thread scheduler was introduced. [Feature #19842]
    • M Ruby threads are managed by N native threads (OS threads) so the thread creation and management cost are reduced.
    • It can break C-extension compatibility so that M:N thread scheduler is disabled on the main Ractor by default.
      • RUBY_MN_THREADS=1 environment variable enables M:N threads on the main Ractor.
      • M:N threads are enabled on non-main Ractors.
    • RUBY_MAX_CPU=n environment variable sets maximum number of N (maximum number of native threads). The default value is 8.
      • Since only one Ruby thread per Ractor can run at the same time, the number of native threads will be used, which is the smaller of the number specified in RUBY_MAX_CPU and the number of running Ractors. So that single Ractor applications (most of applications) will use 1 native thread.
      • To support blocking operations, more than N native threads can be used.

Other Notable New Features


Performance improvements

  • defined?(@ivar) is optimized with Object Shapes.
  • Name resolution such as Socket.getaddrinfo can now be interrupted (in environments where pthreads are available). Feature #19965
    • For this purpose, a pthread is now created whenever calling getaddrinfo or getnameinfo. This incurs some overhead in name resolution (about 2.5x in our experiments). We do not expect the name resolution overhead to be a problem for most applications, but if you observe such, or if you see unexpected affects that you believe are due to this change, please report them.
  • Environment variable RUBY_GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO has been added. Feature #19571
  • Children of old objects are no longer immediately promoted to the old generation in the garbage collector. Feature #19678
  • Support for weak references has been added to the garbage collector. Feature #19783

Other notable changes since 3.2


IRB has received several enhancements, including but not limited to:

  • Advanced irb:rdbg integration that provides an equivalent debugging experience to pry-byebug (doc).
  • Pager support for ls, show_source and show_cmds commands.
  • More accurate and helpful information provided by the ls and show_source commands.
  • Experimental autocompletion using type analysis (doc).
  • It is now possible to change the font color and font style in the completion dialog by a newly introduced class Reline::Face (doc)

In addition, IRB has also undergone extensive refactoring and received dozens of bug fixes to facilitate easier future enhancements.

Compatibility issues

Note: Excluding feature bug fixes.

Removed constants

The following deprecated constants are removed.

Removed methods

The following deprecated methods are removed.

Removed environment variables

The following deprecated environment variables are removed.

  • Environment variable RUBY_GC_HEAP_INIT_SLOTS has been deprecated and is a no-op. Please use environment variables RUBY_GC_HEAP_{0,1,2,3,4}_INIT_SLOTS instead. Feature #19785

Stdlib compatibility issues

ext/readline is retired

  • We have reline that is pure Ruby implementation compatible with ext/readline API. We rely on reline in the future. If you need to use ext/readline, you can install ext/readline via with gem install readline-ext.
  • We no longer need to install libraries like libreadline or libedit.

C API updates

Updated C APIs

The following APIs are updated.

Removed C APIs

The following deprecated APIs are removed.

Standard library updates

RubyGems and Bundler warn if users require gem that is scheduled to become the bundled gems in the future version of Ruby.

Targeted libraries are:

  • abbrev
  • base64
  • bigdecimal
  • csv
  • drb
  • getoptlong
  • mutex_m
  • nkf
  • observer
  • racc
  • resolv-replace
  • rinda
  • syslog

The following default gem is added.

  • prism 0.15.1

The following default gems are updated.

  • RubyGems
  • base64 0.2.0
  • benchmark 0.3.0
  • bigdecimal 3.1.5
  • bundler
  • cgi 0.4.0
  • csv 3.2.8
  • date 3.3.4
  • delegate 0.3.1
  • drb 2.2.0
  • english 0.8.0
  • erb 4.0.3
  • etc
  • fcntl 1.1.0
  • fiddle 1.1.2
  • fileutils 1.7.2
  • find 0.2.0
  • getoptlong 0.2.1
  • io-console
  • irb 1.8.3
  • logger 1.6.0
  • mutex_m 0.2.0
  • net-http 0.4.0
  • net-protocol 0.2.2
  • nkf 0.1.3
  • observer 0.1.2
  • open-uri 0.4.0
  • open3 0.2.0
  • openssl 3.2.0
  • optparse 0.4.0
  • ostruct 0.6.0
  • pathname 0.3.0
  • pp 0.5.0
  • prettyprint 0.2.0
  • pstore 0.1.3
  • psych
  • rdoc 6.6.0
  • reline 0.3.9
  • rinda 0.2.0
  • securerandom 0.3.0
  • shellwords 0.2.0
  • singleton 0.2.0
  • stringio 3.0.9
  • strscan 3.0.7
  • syntax_suggest 1.1.0
  • tempfile 0.2.0
  • time 0.3.0
  • timeout 0.4.1
  • tmpdir 0.2.0
  • tsort 0.2.0
  • un 0.3.0
  • uri 0.13.0
  • weakref 0.1.3
  • win32ole 1.8.10
  • yaml 0.3.0
  • zlib 3.1.0

The following bundled gem is promoted from default gems.

  • racc 1.7.3

The following bundled gems are updated.

  • minitest 5.20.0
  • rake 13.1.0
  • test-unit 3.6.1
  • rexml 3.2.6
  • rss 0.3.0
  • net-imap 0.4.4
  • net-smtp 0.4.0
  • rbs 3.2.2
  • typeprof 0.21.8
  • debug 1.8.0

See GitHub releases like Logger or changelog for details of the default gems or bundled gems.

See NEWS or commit logs for more details.

With those changes, 5207 files changed, 284820 insertions(+), 174773 deletions(-) since Ruby 3.2.0!



    SIZE: 21550473
    SHA1: 2811f191d66dffee0206771873bd990857ae4ed6
    SHA256: 0969141be92e67e0edb84a8fb354acc98f01bd78e602a23a0f136045c82f4809
    SHA512: 94db07a6958c09809b2e5b597fa55a121074e8bacb3bf588c83cf0d35b07a8b070172035a49d1abf0d8ee364a9ace824f34e677f7327ffe1acdbab0938ac49c4

    SIZE: 15970144
    SHA1: 496600612605f8ebeb955255e98bac73a4cbc045
    SHA256: f79afcf122dc7d04fe26cfa4436b9c488b21766fc54b0d2dfb2ba41cd0cdd355
    SHA512: d7ab0d703e7884efd31045933409cd68fac1d9941963537ccc8e309ca7c8bee8500a68182135acba22cbdbf4a8ae99f39bf7f0925273eb4fbc3728c0c1ba0c19

    SIZE: 26618303
    SHA1: 6a13e08c7e484d42037c1e2c87c5d0e220f893a0
    SHA256: c35bf637a647c2f60148368ffb374db5c258570911794f46b6dfdb98ebfe95d9
    SHA512: c4ef2cdcdadeb85ad1d42aedc97f9f3d609b3b01eea2319451cf92c81bd31ae8129b7c91fc68571469dd888c01ea0f48f73234b965db17f6a87404ca382f7794

What is Ruby

Ruby was first developed by Matz (Yukihiro Matsumoto) in 1993, and is now developed as Open Source. It runs on multiple platforms and is used all over the world especially for web development.