diff --git a/encoding.c b/encoding.c
index 8bb393b471ed54..e9510fe3c146c5 100644
--- a/encoding.c
+++ b/encoding.c
@@ -1367,7 +1367,7 @@ enc_names_i(st_data_t name, st_data_t idx, st_data_t args)
     VALUE *arg = (VALUE *)args;
 
     if ((int)idx == (int)arg[0]) {
-        VALUE str = rb_interned_str_cstr((char *)name);
+        VALUE str = rb_enc_interned_str_cstr((char *)name, rb_usascii_encoding());
         rb_ary_push(arg[1], str);
     }
     return ST_CONTINUE;
@@ -1873,7 +1873,7 @@ static int
 rb_enc_name_list_i(st_data_t name, st_data_t idx, st_data_t arg)
 {
     VALUE ary = (VALUE)arg;
-    VALUE str = rb_interned_str_cstr((char *)name);
+    VALUE str = rb_enc_interned_str_cstr((char *)name, rb_usascii_encoding());
     rb_ary_push(ary, str);
     return ST_CONTINUE;
 }
@@ -1921,7 +1921,7 @@ rb_enc_aliases_enc_i(st_data_t name, st_data_t orig, st_data_t arg)
         str = rb_fstring_cstr(rb_enc_name(enc));
         rb_ary_store(ary, idx, str);
     }
-    key = rb_interned_str_cstr((char *)name);
+    key = rb_enc_interned_str_cstr((char *)name, rb_usascii_encoding());
     rb_hash_aset(aliases, key, str);
     return ST_CONTINUE;
 }
diff --git a/ext/io/console/console.c b/ext/io/console/console.c
index 7ddaf071a8833a..2b0193bb90b631 100644
--- a/ext/io/console/console.c
+++ b/ext/io/console/console.c
@@ -84,9 +84,9 @@ getattr(int fd, conmode *t)
 static ID id_getc, id_close;
 static ID id_gets, id_flush, id_chomp_bang;
 
-#ifndef HAVE_RB_INTERNED_STR_CSTR
+#ifndef HAVE_RB_ENC_INTERNED_STR_CSTR
 # define rb_str_to_interned_str(str) rb_str_freeze(str)
-# define rb_interned_str_cstr(str) rb_str_freeze(rb_usascii_str_new_cstr(str))
+# define rb_enc_interned_str_cstr(str, enc) rb_str_freeze(rb_usascii_str_new_cstr(str))
 #endif
 
 #if defined HAVE_RUBY_FIBER_SCHEDULER_H
@@ -1897,7 +1897,7 @@ console_ttyname(VALUE io)
 	size_t size = sizeof(termname);
 	int e;
 	if (ttyname_r(fd, tn, size) == 0)
-	    return rb_interned_str_cstr(tn);
+	    return rb_enc_interned_str_cstr(tn, rb_usascii_encoding());
 	if ((e = errno) == ERANGE) {
 	    VALUE s = rb_str_new(0, size);
 	    while (1) {
@@ -1921,7 +1921,7 @@ console_ttyname(VALUE io)
 	    int e = errno;
 	    rb_syserr_fail_str(e, rb_sprintf("ttyname(%d)", fd));
 	}
-	return rb_interned_str_cstr(tn);
+	return rb_enc_interned_str_cstr(tn, rb_usascii_encoding());
     }
 # else
 #   error No ttyname function
diff --git a/ext/io/console/extconf.rb b/ext/io/console/extconf.rb
index dd3d221ae51df3..e6254c9e90fe98 100644
--- a/ext/io/console/extconf.rb
+++ b/ext/io/console/extconf.rb
@@ -9,7 +9,7 @@
 have_func("rb_syserr_new_str(0, Qnil)") or
   abort
 
-have_func("rb_interned_str_cstr")
+have_func("rb_enc_interned_str_cstr")
 have_func("rb_io_path", "ruby/io.h")
 have_func("rb_io_descriptor", "ruby/io.h")
 have_func("rb_io_get_write_io", "ruby/io.h")
diff --git a/gc/default/default.c b/gc/default/default.c
index be5385f166fde1..45c0d3e2552fef 100644
--- a/gc/default/default.c
+++ b/gc/default/default.c
@@ -505,7 +505,6 @@ typedef struct rb_objspace {
         unsigned int during_compacting : 1;
         unsigned int during_reference_updating : 1;
         unsigned int gc_stressful: 1;
-        unsigned int has_newobj_hook: 1;
         unsigned int during_minor_gc : 1;
         unsigned int during_incremental_marking : 1;
         unsigned int measure_gc : 1;
@@ -1520,7 +1519,6 @@ rb_gc_impl_set_event_hook(void *objspace_ptr, const rb_event_flag_t event)
 {
     rb_objspace_t *objspace = objspace_ptr;
     objspace->hook_events = event & RUBY_INTERNAL_EVENT_OBJSPACE_MASK;
-    objspace->flags.has_newobj_hook = !!(objspace->hook_events & RUBY_INTERNAL_EVENT_NEWOBJ);
 }
 
 unsigned long long
@@ -3812,7 +3810,7 @@ gc_sweep_finish_heap(rb_objspace_t *objspace, rb_heap_t *heap)
                     heap_allocatable_slots_expand(objspace, heap, swept_slots, heap->total_slots);
                 }
             }
-            else {
+            else if (objspace->heap_pages.allocatable_slots < (min_free_slots - swept_slots)) {
                 gc_needs_major_flags |= GPR_FLAG_MAJOR_BY_NOFREE;
                 heap->force_major_gc_count++;
             }
@@ -9584,7 +9582,7 @@ rb_gc_impl_init(void)
         VALUE opts;
         /* \GC build options */
         rb_define_const(rb_mGC, "OPTS", opts = rb_ary_new());
-#define OPT(o) if (o) rb_ary_push(opts, rb_interned_str(#o, sizeof(#o) - 1))
+#define OPT(o) if (o) rb_ary_push(opts, rb_enc_interned_str(#o, sizeof(#o) - 1, rb_usascii_encoding()))
         OPT(GC_DEBUG);
         OPT(USE_RGENGC);
         OPT(RGENGC_DEBUG);
diff --git a/imemo.c b/imemo.c
index 8b3018523f0155..d949466a776f3d 100644
--- a/imemo.c
+++ b/imemo.c
@@ -94,8 +94,9 @@ rb_free_tmp_buffer(volatile VALUE *store)
     rb_imemo_tmpbuf_t *s = (rb_imemo_tmpbuf_t*)ATOMIC_VALUE_EXCHANGE(*store, 0);
     if (s) {
         void *ptr = ATOMIC_PTR_EXCHANGE(s->ptr, 0);
+        long cnt = s->cnt;
         s->cnt = 0;
-        ruby_xfree(ptr);
+        ruby_sized_xfree(ptr, sizeof(VALUE) * cnt);
     }
 }
 
diff --git a/lib/prism/prism.gemspec b/lib/prism/prism.gemspec
index 463387e55c814b..283c7b04aa95e6 100644
--- a/lib/prism/prism.gemspec
+++ b/lib/prism/prism.gemspec
@@ -104,6 +104,7 @@ Gem::Specification.new do |spec|
     "lib/prism/translation/parser/compiler.rb",
     "lib/prism/translation/parser/lexer.rb",
     "lib/prism/translation/ripper.rb",
+    "lib/prism/translation/ripper/filter.rb",
     "lib/prism/translation/ripper/lexer.rb",
     "lib/prism/translation/ripper/sexp.rb",
     "lib/prism/translation/ripper/shim.rb",
diff --git a/lib/prism/translation/ripper.rb b/lib/prism/translation/ripper.rb
index 6552d2dbb80794..c8f9fa7731a539 100644
--- a/lib/prism/translation/ripper.rb
+++ b/lib/prism/translation/ripper.rb
@@ -437,6 +437,7 @@ def self.sexp_raw(src, filename = "-", lineno = 1, raise_errors: false)
         end
       end
 
+      autoload :Filter, "prism/translation/ripper/filter"
       autoload :Lexer, "prism/translation/ripper/lexer"
       autoload :SexpBuilder, "prism/translation/ripper/sexp"
       autoload :SexpBuilderPP, "prism/translation/ripper/sexp"
diff --git a/lib/prism/translation/ripper/filter.rb b/lib/prism/translation/ripper/filter.rb
new file mode 100644
index 00000000000000..19deef2d37dfaa
--- /dev/null
+++ b/lib/prism/translation/ripper/filter.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module Prism
+  module Translation
+    class Ripper
+      class Filter # :nodoc:
+        # :stopdoc:
+        def initialize(src, filename = '-', lineno = 1)
+          @__lexer = Lexer.new(src, filename, lineno)
+          @__line = nil
+          @__col = nil
+          @__state = nil
+        end
+
+        def filename
+          @__lexer.filename
+        end
+
+        def lineno
+          @__line
+        end
+
+        def column
+          @__col
+        end
+
+        def state
+          @__state
+        end
+
+        def parse(init = nil)
+          data = init
+          @__lexer.lex.each do |pos, event, tok, state|
+            @__line, @__col = *pos
+            @__state = state
+            data = if respond_to?(event, true)
+                  then __send__(event, tok, data)
+                  else on_default(event, tok, data)
+                  end
+          end
+          data
+        end
+
+        private
+
+        def on_default(event, token, data)
+          data
+        end
+        # :startdoc:
+      end
+    end
+  end
+end
diff --git a/lib/prism/translation/ripper/lexer.rb b/lib/prism/translation/ripper/lexer.rb
index 787181b5a7fc42..bd40fb4c5a2de0 100644
--- a/lib/prism/translation/ripper/lexer.rb
+++ b/lib/prism/translation/ripper/lexer.rb
@@ -100,21 +100,17 @@ def to_a
           end
         end
 
-        def initialize(...)
-          super
-          @lex_compat = Prism.lex_compat(@source, filepath: filename, line: lineno)
+        # Pretty much just the same as Prism.lex_compat.
+        def lex(raise_errors: false)
+          Ripper.lex(@source, filename, lineno, raise_errors: raise_errors)
         end
 
         # Returns the lex_compat result wrapped in `Elem`. Errors are omitted.
         # Since ripper is a streaming parser, tokens are expected to be emitted in the order
         # that the parser encounters them. This is not implemented.
-        def parse(raise_errors: false)
-          if @lex_compat.failure? && raise_errors
-            raise SyntaxError, @lex_compat.errors.first.message
-          else
-            @lex_compat.value.map do |position, event, token, state|
-              Elem.new(position, event, token, state.to_int)
-            end
+        def parse(...)
+          lex(...).map do |position, event, token, state|
+            Elem.new(position, event, token, state.to_int)
           end
         end
 
diff --git a/string.c b/string.c
index 6f4ea03fb37a41..d564c2e2e1bf94 100644
--- a/string.c
+++ b/string.c
@@ -12709,7 +12709,7 @@ VALUE
 rb_interned_str(const char *ptr, long len)
 {
     struct RString fake_str = {RBASIC_INIT};
-    return register_fstring(setup_fake_str(&fake_str, ptr, len, ENCINDEX_US_ASCII), true, false);
+    return register_fstring(setup_fake_str(&fake_str, ptr, len, ENCINDEX_ASCII_8BIT), true, false);
 }
 
 VALUE
diff --git a/test/prism/ruby/ripper_test.rb b/test/prism/ruby/ripper_test.rb
index cac20a073db61b..2a0504c19f35f0 100644
--- a/test/prism/ruby/ripper_test.rb
+++ b/test/prism/ruby/ripper_test.rb
@@ -59,7 +59,7 @@ class RipperTest < TestCase
       "whitequark/slash_newline_in_heredocs.txt"
     ]
 
-    omitted_lexer_parse = [
+    omitted_lex = [
       "comments.txt",
       "heredoc_percent_q_newline_delimiter.txt",
       "heredoc_with_escaped_newline_at_start.txt",
@@ -80,8 +80,20 @@ class RipperTest < TestCase
       define_method("#{fixture.test_name}_sexp_raw") { assert_ripper_sexp_raw(fixture.read) }
     end
 
-    Fixture.each_for_current_ruby(except: incorrect | omitted_lexer_parse) do |fixture|
-      define_method("#{fixture.test_name}_lexer_parse") { assert_ripper_lexer_parse(fixture.read) }
+    Fixture.each_for_current_ruby(except: incorrect | omitted_lex) do |fixture|
+      define_method("#{fixture.test_name}_lex") { assert_ripper_lex(fixture.read) }
+    end
+
+    def test_lexer
+      lexer = Translation::Ripper::Lexer.new("foo")
+      expected = [[1, 0], :on_ident, "foo", Translation::Ripper::EXPR_CMDARG]
+
+      assert_equal([expected], lexer.lex)
+      assert_equal(expected, lexer.parse[0].to_a)
+      assert_equal(lexer.parse[0].to_a, lexer.scan[0].to_a)
+
+      assert_equal(%i[on_int on_op], Translation::Ripper::Lexer.new("1 +").lex.map(&:event))
+      assert_raise(SyntaxError) { Translation::Ripper::Lexer.new("1 +").lex(raise_errors: true) }
     end
 
     def test_tokenize
@@ -106,15 +118,15 @@ def assert_ripper_sexp_raw(source)
       assert_equal Ripper.sexp_raw(source), Prism::Translation::Ripper.sexp_raw(source)
     end
 
-    def assert_ripper_lexer_parse(source)
-      prism = Translation::Ripper::Lexer.new(source).parse
-      ripper = Ripper::Lexer.new(source).parse
-      ripper.reject! { |elem| elem.event == :on_sp } # Prism doesn't emit on_sp
-      ripper.sort_by!(&:pos) # Prism emits tokens by their order in the code, not in parse order
+    def assert_ripper_lex(source)
+      prism = Translation::Ripper.lex(source)
+      ripper = Ripper.lex(source)
+      ripper.reject! { |elem| elem[1] == :on_sp } # Prism doesn't emit on_sp
+      ripper.sort_by! { |elem| elem[0] } # Prism emits tokens by their order in the code, not in parse order
 
       [prism.size, ripper.size].max.times do |i|
-        expected = ripper[i].to_a
-        actual = prism[i].to_a
+        expected = ripper[i]
+        actual = prism[i]
         # Since tokens related to heredocs are not emitted in the same order,
         # the state also doesn't line up.
         if expected[1] == :on_heredoc_end && actual[1] == :on_heredoc_end