diff --git a/dev-lang/ruby/Manifest b/dev-lang/ruby/Manifest
index 2d1078ca2ab33..074865b145cf2 100644
--- a/dev-lang/ruby/Manifest
+++ b/dev-lang/ruby/Manifest
@@ -7,3 +7,4 @@ DIST ruby-3.3.9.tar.xz 16436904 BLAKE2B 1f809d982f0ac60025ac98d2ded28697f1e68eb6
 DIST ruby-3.4.6.tar.xz 17303436 BLAKE2B 1e3b85780821c9df4f82382b7f48b1c543fb8031595de46d0dd33aeb7a2719b4a03ca29d39def056c6040f27e4dc3ca442035e0febb5fb8def8ef837b10786e7 SHA512 29000b3396ab95fc2dc13d2d78441ff5c34258e5421115181c54b1b4d55d5c0d4f3d0c3cec6b32b9a1bb8de5c51b383fcad4369ec3fb244fd0ce182afbe79ba4
 DIST ruby-3.4.7.tar.xz 17312044 BLAKE2B 27732452672e30c5d3d11b6aa6f6e3ebf1c363492145c3e43244804e522d83230f68075d81c6361b4504ad4b9dcb5ac23335412d1f290c03c44a83f940024e8b SHA512 a6b99a2f1d0115d5e7efa710da440b9066c524c335928367c80852630f8db5da36c0a82d6e7ace90e8c40cb20c6097cbdca15a51c343254cadf5f0adf60f8505
 DIST ruby-3.4.8.tar.xz 17320860 BLAKE2B e40144cea391c32a4ce1e6c576884dd9ca3a31398b0110bb67e96eca90dc1d8cb0376269e691a1b48b06bbbb23b0137e67bd05ae4aeccb5c26d163fbce5cec55 SHA512 b6289654685c2d381d15123cf07a131fd088edf13a5336966af5a2e8fad9adda42d14caa7bb0998331831af71e35c546091db55c82089e89b9508603ff5f92d6
+DIST ruby-4.0.0.tar.xz 18008368 BLAKE2B 6d195b39f53cd23eca2e5f06fee5e118b73ef8574739903c39bb1b3325d968ad59a17bfe622bc1790a1bb221ca3ae46220850a95fa539a7a9fb2cf2e8930a65f SHA512 2d5b2e566eaf70a5f3ea6ce6afc0611c0415de58a41336ef7a0b855c9a91eda9aa790a5f8b48e40a1eb9d50f8ea0f687216e617f16c8d040a08474f3116518a4
diff --git a/dev-lang/ruby/files/4.0/010-default-gem-location.patch b/dev-lang/ruby/files/4.0/010-default-gem-location.patch
new file mode 100644
index 0000000000000..36009ad66f61e
--- /dev/null
+++ b/dev-lang/ruby/files/4.0/010-default-gem-location.patch
@@ -0,0 +1,11 @@
+--- a/tool/rbinstall.rb	2022-11-13 08:12:27.373041649 +0100
++++ b/tool/rbinstall.rb	2022-11-13 08:16:09.110406705 +0100
+@@ -994,7 +994,7 @@
+ end
+ 
+ install?(:ext, :comm, :gem, :'bundled-gems') do
+-  gem_dir = Gem.default_dir
++  gem_dir = ENV['GEM_DESTDIR']
+   install_dir = with_destdir(gem_dir)
+   prepare "bundled gems", gem_dir
+   RbInstall.no_write do
diff --git a/dev-lang/ruby/files/4.0/901-musl-stacksize.patch b/dev-lang/ruby/files/4.0/901-musl-stacksize.patch
new file mode 100644
index 0000000000000..f18aa271ea65d
--- /dev/null
+++ b/dev-lang/ruby/files/4.0/901-musl-stacksize.patch
@@ -0,0 +1,20 @@
+--- a/thread_pthread.c	2023-02-08 05:02:20.000000000 +0100
++++ b/thread_pthread.c	2023-03-10 17:46:25.694739053 +0100
+@@ -1033,7 +1033,7 @@
+ {
+     native_main_thread.id = pthread_self();
+ 
+-#if MAINSTACKADDR_AVAILABLE
++#if MAINSTACKADDR_AVAILABLE && !(defined(__linux__) && !defined(__GLIBC__))
+     if (native_main_thread.stack_maxsize) return;
+     {
+         void* stackaddr;
+@@ -2090,7 +2090,7 @@
+ 
+ #ifdef STACKADDR_AVAILABLE
+     if (get_stack(&base, &size) == 0) {
+-# ifdef __APPLE__
++# if defined(__APPLE__) || (defined(__linux__) && !defined(__GLIBC__))
+         if (pthread_equal(th->nt->thread_id, native_main_thread.id)) {
+             struct rlimit rlim;
+             if (getrlimit(RLIMIT_STACK, &rlim) == 0 && rlim.rlim_cur > size) {
diff --git a/dev-lang/ruby/files/4.0/902-hppa-pthread-stack-size.patch b/dev-lang/ruby/files/4.0/902-hppa-pthread-stack-size.patch
new file mode 100644
index 0000000000000..96e24a340ad9c
--- /dev/null
+++ b/dev-lang/ruby/files/4.0/902-hppa-pthread-stack-size.patch
@@ -0,0 +1,54 @@
+https://bugs.gentoo.org/701494
+
+From 40ccf3b91071d3603335b0b7095613ef1843f9e1 Mon Sep 17 00:00:00 2001
+From: Sam James <sam@gentoo.org>
+Date: Fri, 7 Apr 2023 11:46:12 +0100
+Subject: [PATCH] thread_pthread: Grow main_stack if required (fixes tests on
+ HPPA)
+
+On HPPA, test_insns.rb fails (along with various Ruby gems) with
+'stack level too deep (SystemStackError)'. This turns out to be because HPPA
+defaults to a small(er) stack.
+
+With this change, most of Ruby's test suite now passes on HPPA.
+
+Thanks to both Dave and Helge for the investigation and coming up with the
+patch.
+
+Bug: https://bugs.gentoo.org/701494
+Bug: https://bugs.debian.org/881773
+Bug: https://bugs.debian.org/881772 (for PPC64)
+Bug: https://github.com/rack/rack/issues/1640
+Thanks-to: John David Anglin <dave.anglin@bell.net>
+Thanks-to: Helge Deller <deller@gmx.de>
+Signed-off-by: Sam James <sam@gentoo.org>
+--- a/thread_pthread.c
++++ b/thread_pthread.c
+@@ -858,8 +858,22 @@ size_t pthread_get_stacksize_np(pthread_t);
+ #   define MAINSTACKADDR_AVAILABLE 0
+ # endif
+ #endif
+-#if MAINSTACKADDR_AVAILABLE && !defined(get_main_stack)
+-# define get_main_stack(addr, size) get_stack(addr, size)
++#if MAINSTACKADDR_AVAILABLE
++static int get_stack(void **, size_t *);
++static int
++get_main_stack(void **addr, size_t *size)
++{
++    int ret = get_stack(addr, size);
++
++#ifdef __hppa__
++    /* On some architectures, the initial stack size may be too small, but fortunately,
++       it's growable. Bump it up to the minimum needed if it is too small. */
++    if (*size < RUBY_VM_THREAD_VM_STACK_SIZE)
++        *size = RUBY_VM_THREAD_VM_STACK_SIZE;
++#endif
++
++    return ret;
++}
+ #endif
+ 
+ #ifdef STACKADDR_AVAILABLE
+-- 
+2.40.0
+
diff --git a/dev-lang/ruby/ruby-4.0.0.ebuild b/dev-lang/ruby/ruby-4.0.0.ebuild
new file mode 100644
index 0000000000000..9f6ed041a92bf
--- /dev/null
+++ b/dev-lang/ruby/ruby-4.0.0.ebuild
@@ -0,0 +1,330 @@
+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+RUST_MIN_VER="1.85.0"
+RUST_OPTIONAL="yes"
+
+inherit autotools flag-o-matic multiprocessing toolchain-funcs rust
+
+MY_P="${PN}-$(ver_cut 1-3)"
+
+DESCRIPTION="An object-oriented scripting language"
+HOMEPAGE="https://www.ruby-lang.org/"
+SRC_URI="https://cache.ruby-lang.org/pub/ruby/$(ver_cut 1-2)/${MY_P}.tar.xz"
+S=${WORKDIR}/${MY_P}
+
+LICENSE="|| ( Ruby-BSD BSD-2 )"
+SLOT=$(ver_cut 1-2)
+MY_SUFFIX=$(ver_rs 1 '' ${SLOT})
+RUBYVERSION=${SLOT}.0
+
+KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~loong ~mips ~ppc ~ppc64 ~riscv ~s390 ~sparc ~x86 ~arm64-macos ~x64-macos ~x64-solaris"
+IUSE="berkdb debug doc examples gdbm jemalloc jit socks5 +ssl static-libs systemtap tk valgrind xemacs"
+
+RDEPEND="
+	berkdb? ( sys-libs/db:= )
+	gdbm? ( sys-libs/gdbm:= )
+	jemalloc? ( dev-libs/jemalloc:= )
+	jit? ( ${RUST_DEPEND} )
+	ssl? (
+		dev-libs/openssl:0=
+	)
+	socks5? ( >=net-proxy/dante-1.1.13 )
+	systemtap? ( dev-debug/systemtap )
+	tk? (
+		dev-lang/tcl:0=[threads]
+		dev-lang/tk:0=[threads]
+	)
+	dev-libs/libyaml
+	dev-libs/libffi:=
+	virtual/zlib:=
+	virtual/libcrypt:=
+	>=app-eselect/eselect-ruby-20251225
+"
+
+DEPEND="
+	${RDEPEND}
+	valgrind? ( dev-debug/valgrind )
+"
+
+BUNDLED_GEMS="
+	>=dev-ruby/minitest-6.0.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/power_assert-3.0.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/rake-13.3.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/test-unit-3.7.5[ruby_targets_ruby40(-)]
+	>=dev-ruby/rexml-3.4.4[ruby_targets_ruby40(-)]
+	>=dev-ruby/rss-0.3.2[ruby_targets_ruby40(-)]
+	>=dev-ruby/net-ftp-0.3.9[ruby_targets_ruby40(-)]
+	>=dev-ruby/net-imap-0.6.2[ruby_targets_ruby40(-)]
+	>=dev-ruby/net-pop-0.1.2[ruby_targets_ruby40(-)]
+	>=dev-ruby/net-smtp-0.5.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/matrix-0.4.3[ruby_targets_ruby40(-)]
+	>=dev-ruby/prime-0.1.4[ruby_targets_ruby40(-)]
+	>=dev-ruby/rbs-3.10.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/typeprof-0.31.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/debug-1.11.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/racc-1.8.1[ruby_targets_ruby40(-)]
+
+	>=dev-ruby/mutex_m-0.3.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/getoptlong-0.2.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/base64-0.3.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/bigdecimal-4.0.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/observer-0.1.2[ruby_targets_ruby40(-)]
+	>=dev-ruby/abbrev-0.1.2[ruby_targets_ruby40(-)]
+	>=dev-ruby/resolv-replace-0.1.1[ruby_targets_ruby40(-)]
+	>=dev-ruby/rinda-0.2.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/drb-2.2.3[ruby_targets_ruby40(-)]
+	>=dev-ruby/nkf-0.2.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/syslog-0.3.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/csv-3.3.5[ruby_targets_ruby40(-)]
+	>=dev-ruby/repl_type_completor-0.1.12[ruby_targets_ruby40(-)]
+"
+# ostruct             0.6.3   https://github.com/ruby/ostruct
+# pstore              0.2.0   https://github.com/ruby/pstore
+# benchmark           0.5.0   https://github.com/ruby/benchmark
+# logger              1.7.0   https://github.com/ruby/logger
+# rdoc                7.0.3   https://github.com/ruby/rdoc
+# win32ole            1.9.2   https://github.com/ruby/win32ole
+# irb                 1.16.0  https://github.com/ruby/irb
+# reline              0.6.3   https://github.com/ruby/reline
+# readline            0.0.4   https://github.com/ruby/readline
+# fiddle              1.1.8   https://github.com/ruby/fiddle
+
+PDEPEND="
+	${BUNDLED_GEMS}
+	virtual/rubygems[ruby_targets_ruby40(-)]
+	>=dev-ruby/bundler-4.0.3[ruby_targets_ruby40(-)]
+	>=dev-ruby/did_you_mean-2.0.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/irb-1.16.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/json-2.18.0[ruby_targets_ruby40(-)]
+	>=dev-ruby/rdoc-7.0.2[ruby_targets_ruby40(-)]
+	xemacs? ( app-xemacs/ruby-modes )
+"
+
+pkg_setup() {
+	use jit && rust_pkg_setup
+}
+
+src_prepare() {
+	eapply "${FILESDIR}"/"${SLOT}"/010*.patch
+	eapply "${FILESDIR}"/"${SLOT}"/902*.patch
+
+	if use elibc_musl ; then
+		eapply "${FILESDIR}"/${SLOT}/901-musl-*.patch
+	fi
+
+	einfo "Unbundling gems..."
+	cd "$S"
+	# Remove bundled gems that we will install via PDEPEND, bug
+	# 539700.
+	rm -fr gems/* || die
+	touch gems/bundled_gems || die
+
+	# Remove tests that are known to fail or require a network connection
+	rm -f test/ruby/test_process.rb test/rubygems/test_gem{,_path_support}.rb || die
+	rm -f test/rubygems/test_bundled_ca.rb || die
+	rm -f test/rinda/test_rinda.rb test/socket/test_tcp.rb test/fiber/test_address_resolve.rb \
+	   spec/ruby/library/socket/tcpsocket/{initialize,open}_spec.rb \
+		spec/ruby/library/socket/socket/connect_spec.rb || die
+
+v	# Remove webrick tests because setting LD_LIBRARY_PATH does not work for them.
+	rm -rf tool/test/webrick || die
+
+	# Avoid testing against hard-coded blockdev devices that most likely are not available
+	sed -i -e '/def blockdev/a@blockdev = nil' test/ruby/test_file_exhaustive.rb || die
+
+	# Avoid tests that require gem downloads
+	sed -e '/^check/ s/\(test-syntax-suggest\|\$(PREPARE_SYNTAX_SUGGEST)\)//g' \
+		-i common.mk || die
+
+	# Avoid test that fails intermittently
+	sed -e '/test_gem_exec_gem_uninstall/aomit "Fails intermittently"' \
+		-i test/rubygems/test_gem_commands_exec_command.rb || die
+
+	# Avoid test fragile for git command output not matching on whitespace
+	sed -e '/test_pretty_print/aomit "Fragile for output differences"' \
+		-i test/rubygems/test_gem_source_git.rb || die
+
+	# Avoid tests that don't expect our ruby40 executable name.
+	sed -e '/test_prelude_gems_and_loaded_features/aomit "Does not match ruby40"' \
+		-i test/ruby/test_box.rb
+
+	# Avoid specs that require gems to be installed already due to our unbundling.
+	rm -rf spec/ruby/library/irb || die
+
+	if use prefix ; then
+		# Fix hardcoded SHELL var in mkmf library
+		sed -i -e "s#\(SHELL = \).*#\1${EPREFIX}/bin/sh#" lib/mkmf.rb || die
+	fi
+
+	eapply_user
+
+	eautoreconf
+}
+
+src_configure() {
+	local modules="win32,win32ole" myconf=
+
+	# Ruby's build system does interesting things with MAKEOPTS and doesn't
+	# handle MAKEOPTS="-Oline" or similar well. Just filter it all out
+	# and use -j/-l parsed out from the original MAKEOPTS, then use that.
+	# Newer Portage sets this option by default in GNUMAKEFLAGS if nothing
+	# is set by the user in MAKEOPTS. See bug #900929 and bug #728424.
+	local makeopts_tmp="-j$(makeopts_jobs) -l$(makeopts_loadavg)"
+	unset MAKEOPTS MAKEFLAGS GNUMAKEFLAGS
+	export MAKEOPTS="${makeopts_tmp}"
+
+	# Avoid a hardcoded path to mkdir to avoid issues with mixed
+	# usr-merge and normal binary packages, bug #932386.
+	export ac_cv_path_mkdir=mkdir
+
+	# -fomit-frame-pointer makes ruby segfault, see bug #150413.
+	filter-flags -fomit-frame-pointer
+	append-flags -fno-omit-frame-pointer
+	# In many places aliasing rules are broken; play it safe
+	# as it's risky with newer compilers to leave it as it is.
+	append-flags -fno-strict-aliasing
+	# Workaround for bug #965095 (gcc PR122610)
+	tc-is-gcc && append-flags -fno-ipa-modref
+
+	# Workaround for bug #938302
+	if use systemtap && has_version "dev-debug/systemtap[-dtrace-symlink(+)]" ; then
+		export DTRACE="${BROOT}"/usr/bin/stap-dtrace
+	fi
+
+	# Socks support via dante
+	if use socks5 ; then
+		# Socks support can't be disabled as long as SOCKS_SERVER is
+		# set and socks library is present, so need to unset
+		# SOCKS_SERVER in that case.
+		unset SOCKS_SERVER
+	fi
+
+	# Increase GC_MALLOC_LIMIT if set (default is 8000000)
+	if [ -n "${RUBY_GC_MALLOC_LIMIT}" ] ; then
+		append-flags "-DGC_MALLOC_LIMIT=${RUBY_GC_MALLOC_LIMIT}"
+	fi
+
+	# Determine which modules *not* to build depending in the USE flags.
+	if ! use berkdb ; then
+		modules="${modules},dbm"
+	fi
+	if ! use gdbm ; then
+		modules="${modules},gdbm"
+	fi
+	if ! use ssl ; then
+		modules="${modules},openssl"
+	fi
+	if ! use tk ; then
+		modules="${modules},tk"
+	fi
+
+	# Fix co-routine selection for x32, bug 933070
+	[[ ${CHOST} == *gnux32 ]] && myconf="${myconf} --with-coroutine=amd64"
+
+	# Provide an empty LIBPATHENV because we disable rpath but we do not
+	# need LD_LIBRARY_PATH by default since that breaks USE=multitarget
+	# #564272
+	# except on Darwin, where we really need LIBPATHENV to set the right
+	# DYLD_ stuff during the invocation of miniruby for it to work
+	#
+	# --with-setjmp-type=setjmp for bug #949016
+	[[ ${CHOST} == *-darwin* ]] || export LIBPATHENV=""
+	INSTALL="${EPREFIX}/usr/bin/install -c" econf \
+		--program-suffix=${MY_SUFFIX} \
+		--with-soname=ruby${MY_SUFFIX} \
+		--enable-shared \
+		--enable-pthread \
+		--disable-rpath \
+		--without-baseruby \
+		--with-compress-debug-sections=no \
+		--with-setjmp-type=setjmp \
+		--enable-mkmf-verbose \
+		--with-out-ext="${modules}" \
+		$(use_with jemalloc jemalloc) \
+		$(use_enable jit jit-support) \
+		$(use_enable jit yjit) \
+		$(use_enable socks5 socks) \
+		$(use_enable systemtap dtrace) \
+		$(use_enable doc install-doc) \
+		$(use_enable static-libs static) \
+		$(use_enable static-libs install-static-library) \
+		$(use_with static-libs static-linked-ext) \
+		$(use_enable debug) \
+		${myconf} \
+		$(use_with valgrind) \
+		--enable-option-checking=no
+
+	# Makefile is broken because it lacks -ldl
+	rm -rf ext/-test-/popen_deadlock || die
+}
+
+src_compile() {
+	local -x LD_LIBRARY_PATH="${S}${LD_LIBRARY_PATH+:}${LD_LIBRARY_PATH}"
+	emake V=1 EXTLDFLAGS="${LDFLAGS}" MJIT_CFLAGS="${CFLAGS}" MJIT_OPTFLAGS="" MJIT_DEBUGFLAGS=""
+}
+
+src_test() {
+	local -x LD_LIBRARY_PATH="${S}${LD_LIBRARY_PATH+:}${LD_LIBRARY_PATH}"
+	emake V=1 check
+}
+
+src_install() {
+	# Remove the remaining bundled gems. We do this late in the process
+	# since they are used during the build to e.g. create the
+	# documentation.
+	einfo "Removing default gems before installation"
+	rm -rf lib/bundler* lib/rdoc/rdoc.gemspec || die
+
+	# Ruby is involved in the install process, we don't want interference here.
+	unset RUBYOPT
+
+	local MINIRUBY=$(echo -e 'include Makefile\ngetminiruby:\n\t@echo $(MINIRUBY)'|make -f - getminiruby)
+
+	local -x LD_LIBRARY_PATH="${S}:${ED}/usr/$(get_libdir)${LD_LIBRARY_PATH+:}${LD_LIBRARY_PATH}"
+
+	local -x RUBYLIB="${S}:${ED}/usr/$(get_libdir)/ruby/${RUBYVERSION}"
+	for d in $(find "${S}/ext" -type d) ; do
+		RUBYLIB="${RUBYLIB}:$d"
+	done
+
+	# Create directory for the default gems
+	local gem_home="${EPREFIX}/usr/$(get_libdir)/ruby/gems/${RUBYVERSION}"
+	mkdir -p "${D}/${gem_home}" || die "mkdir gem home failed"
+
+	emake V=1 DESTDIR="${D}" GEM_DESTDIR=${gem_home} install
+
+	# Remove installed rubygems and rdoc copy
+	rm -rf "${ED}/usr/$(get_libdir)/ruby/${RUBYVERSION}/rubygems" || die "rm rubygems failed"
+	rm -rf "${ED}/usr/bin/"gem"${MY_SUFFIX}" || die "rm rdoc bins failed"
+	rm -rf "${ED}/usr/$(get_libdir)/ruby/${RUBYVERSION}"/rdoc* || die "rm rdoc failed"
+	rm -rf "${ED}/usr/bin/"{bundle,bundler,ri,rdoc}"${MY_SUFFIX}" || die "rm rdoc bins failed"
+
+	if use doc; then
+		emake DESTDIR="${D}" GEM_DESTDIR=${gem_home} install-doc
+	fi
+
+	if use examples; then
+		dodoc -r sample
+	fi
+
+	dodoc ChangeLog NEWS.md README*
+	dodoc -r doc
+}
+
+pkg_postinst() {
+	if [[ ! -n $(readlink "${EROOT}"/usr/bin/ruby) ]] ; then
+		eselect ruby set ruby${MY_SUFFIX}
+	fi
+
+	elog
+	elog "To switch between available Ruby profiles, execute as root:"
+	elog "\teselect ruby set ruby(30|31|...)"
+	elog
+}
+
+pkg_postrm() {
+	eselect ruby cleanup
+}