Ruby 3.3.0-rc1 Released

We are pleased to announce the release of Ruby 3.3.0-rc1. 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.

After the release of RC1, we will avoid introducing ABI incompatibilities wherever possible. If we need to do, we’ll announce it in the release note.


  • 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.
  • Code GC is now disabled by default, and --yjit-exec-mem-size is treated as a hard limit where compilation of new code stops.
    • Better copy-on-write behavior on servers using unicorn and forking
    • No sudden drops in performance due to code GC.
    • You can still enable code GC if desired with --yjit-code-gc
  • 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.
  • Several performance improvements to the Garbage Collector
    • Young objects referenced by old objects are no longer immediately promoted to the old generation. This significantly reduces the frequency of major GC collections. [Feature #19678]
    • A new REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO tuning variable was introduced to control the number of unprotected objects cause a major GC collection to trigger. The default is set to 0.01 (1%). This significantly reduces the frequency of major GC collection. [Feature #19571]
    • Write Barriers were implemented for many core types that were missing them, notably Time, Enumerator, MatchData, Method, File::Stat, BigDecimal and several others. This significantly reduces minor GC collection time and major GC collection frequency.
    • Most core classes are now using Variable Width Allocation, notably Hash, Time, Thread::Backtrace, Thread::Backtrace::Location, File::Stat, Method. This makes these classes faster to allocate and free, use less memory and reduce heap fragmentation.
    • 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.

  • it calls without arguments in a block with no ordinary parameters are deprecated. it will be a reference to the first block parameter in Ruby 3.4. Feature #18980

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, 5414 files changed, 306141 insertions(+), 183575 deletions(-) since Ruby 3.2.0!



    SIZE: 21783575
    SHA1: c75a860e06f27b7f69b874757417277c21d1d3f4
    SHA256: c4ff82395a90ef76c7f906b7687026e0ab96b094dcf3a532d9ab97784a073222
    SHA512: 265fb2ffe55af47d8349edffcebe749cc170291227cef55529fe4e67363e4e84b88daa34ffb5364a99c8a0e32110266a34c9a11d62f3bd6f6d47fa76eca641f4

    SIZE: 16163884
    SHA1: 26503f9bdc7d0a05aaa9836f54d3aa9e74a9ead9
    SHA256: 051815637f1fa75a1edf2c54b66d5d5b69563daad777da8dc39543b7754b5290
    SHA512: 82f4acfaad1dc47db27ee3eb952481a95b3474a98059e9e9f5ceb035b690d1faabe99f2ec52371c4089ed1615eb10c395f029088418fec4d26399b65b4f259b9

    SIZE: 26735443
    SHA1: 35583453a7734216b08829ef0ec9ea1bc0d4ae7f
    SHA256: 56dd82e1dd714f2889ca975ae7befbe005675de08839c2cc4a484de2ae65201c
    SHA512: 7fbe414c230aedc9f364512bcbc213038f8f6e4268929a559d2527e2f3e32a140b394e37098ab7e59161236eca8b89cc9e52d73a3be8d7bd44faa91681483f5d

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.