diff --git a/lib/compiler/aro/aro/Compilation.zig b/lib/compiler/aro/aro/Compilation.zig
index 46f783097b..e0b9a508cf 100644
--- a/lib/compiler/aro/aro/Compilation.zig
+++ b/lib/compiler/aro/aro/Compilation.zig
@@ -171,10 +171,11 @@ pub fn init(gpa: Allocator, arena: Allocator, io: Io, diagnostics: *Diagnostics,
 
 /// Initialize Compilation with default environment,
 /// pragma handlers and emulation mode set to target.
-pub fn initDefault(gpa: Allocator, arena: Allocator, diagnostics: *Diagnostics, cwd: std.fs.Dir) !Compilation {
+pub fn initDefault(gpa: Allocator, arena: Allocator, io: Io, diagnostics: *Diagnostics, cwd: std.fs.Dir) !Compilation {
     var comp: Compilation = .{
         .gpa = gpa,
         .arena = arena,
+        .io = io,
         .diagnostics = diagnostics,
         .environment = try Environment.loadAll(gpa),
         .cwd = cwd,
diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index d88a8465d7..57578628fc 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -174,7 +174,7 @@ pub fn io(t: *Threaded) Io {
             .dirStatPath = switch (builtin.os.tag) {
                 .linux => dirStatPathLinux,
                 .windows => @panic("TODO"),
-                .wasi => @panic("TODO"),
+                .wasi => dirStatPathWasi,
                 else => dirStatPathPosix,
             },
             .fileStat = switch (builtin.os.tag) {
@@ -984,6 +984,42 @@ fn dirStatPathPosix(
     }
 }
 
+fn dirStatPathWasi(
+    userdata: ?*anyopaque,
+    dir: Io.Dir,
+    sub_path: []const u8,
+    options: Io.Dir.StatPathOptions,
+) Io.Dir.StatPathError!Io.File.Stat {
+    if (builtin.link_libc) return dirStatPathPosix(userdata, dir, sub_path, options);
+    const t: *Threaded = @ptrCast(@alignCast(userdata));
+    const dir_fd = dir.handle;
+    const wasi = std.os.wasi;
+    const flags: wasi.lookupflags_t = .{
+        .SYMLINK_FOLLOW = @intFromBool(options.follow_symlinks),
+    };
+    var stat: wasi.filestat_t = undefined;
+    while (true) {
+        try t.checkCancel();
+        switch (wasi.path_filestat_get(dir_fd, flags, sub_path.ptr, sub_path.len, &stat)) {
+            .SUCCESS => return statFromWasi(stat),
+            .INTR => continue,
+            .CANCELED => return error.Canceled,
+
+            .INVAL => |err| errnoBug(err),
+            .BADF => |err| errnoBug(err), // Always a race condition.
+            .NOMEM => return error.SystemResources,
+            .ACCES => return error.AccessDenied,
+            .FAULT => |err| errnoBug(err),
+            .NAMETOOLONG => return error.NameTooLong,
+            .NOENT => return error.FileNotFound,
+            .NOTDIR => return error.FileNotFound,
+            .NOTCAPABLE => return error.AccessDenied,
+            .ILSEQ => return error.BadPathName,
+            else => |err| return posix.unexpectedErrno(err),
+        }
+    }
+}
+
 fn fileStatPosix(userdata: ?*anyopaque, file: Io.File) Io.File.StatError!Io.File.Stat {
     const t: *Threaded = @ptrCast(@alignCast(userdata));
 
diff --git a/lib/std/fs/Dir.zig b/lib/std/fs/Dir.zig
index c8236b9f7a..3565d2fc2c 100644
--- a/lib/std/fs/Dir.zig
+++ b/lib/std/fs/Dir.zig
@@ -2500,10 +2500,6 @@ pub fn statFile(self: Dir, sub_path: []const u8) StatFileError!Stat {
         defer file.close();
         return file.stat();
     }
-    if (native_os == .wasi and !builtin.link_libc) {
-        const st = try std.os.fstatat_wasi(self.fd, sub_path, .{ .SYMLINK_FOLLOW = true });
-        return Stat.fromWasi(st);
-    }
     var threaded: Io.Threaded = .init_single_threaded;
     const io = threaded.io();
     return Io.Dir.statPath(.{ .handle = self.fd }, io, sub_path, .{});
diff --git a/lib/std/fs/test.zig b/lib/std/fs/test.zig
index 6bb0d871b6..052afc3a02 100644
--- a/lib/std/fs/test.zig
+++ b/lib/std/fs/test.zig
@@ -2031,37 +2031,28 @@ test "invalid UTF-8/WTF-8 paths" {
             const invalid_path = try ctx.transformPath("\xFF");
 
             try testing.expectError(expected_err, ctx.dir.openFile(invalid_path, .{}));
-            try testing.expectError(expected_err, ctx.dir.openFileZ(invalid_path, .{}));
 
             try testing.expectError(expected_err, ctx.dir.createFile(invalid_path, .{}));
-            try testing.expectError(expected_err, ctx.dir.createFileZ(invalid_path, .{}));
 
             try testing.expectError(expected_err, ctx.dir.makeDir(invalid_path));
-            try testing.expectError(expected_err, ctx.dir.makeDirZ(invalid_path));
 
             try testing.expectError(expected_err, ctx.dir.makePath(invalid_path));
             try testing.expectError(expected_err, ctx.dir.makeOpenPath(invalid_path, .{}));
 
             try testing.expectError(expected_err, ctx.dir.openDir(invalid_path, .{}));
-            try testing.expectError(expected_err, ctx.dir.openDirZ(invalid_path, .{}));
 
             try testing.expectError(expected_err, ctx.dir.deleteFile(invalid_path));
-            try testing.expectError(expected_err, ctx.dir.deleteFileZ(invalid_path));
 
             try testing.expectError(expected_err, ctx.dir.deleteDir(invalid_path));
-            try testing.expectError(expected_err, ctx.dir.deleteDirZ(invalid_path));
 
             try testing.expectError(expected_err, ctx.dir.rename(invalid_path, invalid_path));
-            try testing.expectError(expected_err, ctx.dir.renameZ(invalid_path, invalid_path));
 
             try testing.expectError(expected_err, ctx.dir.symLink(invalid_path, invalid_path, .{}));
-            try testing.expectError(expected_err, ctx.dir.symLinkZ(invalid_path, invalid_path, .{}));
             if (native_os == .wasi) {
                 try testing.expectError(expected_err, ctx.dir.symLinkWasi(invalid_path, invalid_path, .{}));
             }
 
             try testing.expectError(expected_err, ctx.dir.readLink(invalid_path, &[_]u8{}));
-            try testing.expectError(expected_err, ctx.dir.readLinkZ(invalid_path, &[_]u8{}));
             if (native_os == .wasi) {
                 try testing.expectError(expected_err, ctx.dir.readLinkWasi(invalid_path, &[_]u8{}));
             }
@@ -2075,7 +2066,6 @@ test "invalid UTF-8/WTF-8 paths" {
             try testing.expectError(expected_err, ctx.dir.writeFile(.{ .sub_path = invalid_path, .data = "" }));
 
             try testing.expectError(expected_err, ctx.dir.access(invalid_path, .{}));
-            try testing.expectError(expected_err, ctx.dir.accessZ(invalid_path, .{}));
 
             var dir = ctx.dir.adaptToNewApi();
             try testing.expectError(expected_err, dir.updateFile(io, invalid_path, dir, invalid_path, .{}));
@@ -2085,37 +2075,25 @@ test "invalid UTF-8/WTF-8 paths" {
 
             if (native_os != .wasi) {
                 try testing.expectError(expected_err, ctx.dir.realpath(invalid_path, &[_]u8{}));
-                try testing.expectError(expected_err, ctx.dir.realpathZ(invalid_path, &[_]u8{}));
                 try testing.expectError(expected_err, ctx.dir.realpathAlloc(testing.allocator, invalid_path));
             }
 
             try testing.expectError(expected_err, fs.rename(ctx.dir, invalid_path, ctx.dir, invalid_path));
-            try testing.expectError(expected_err, fs.renameZ(ctx.dir, invalid_path, ctx.dir, invalid_path));
 
             if (native_os != .wasi and ctx.path_type != .relative) {
                 try testing.expectError(expected_err, fs.copyFileAbsolute(invalid_path, invalid_path, .{}));
                 try testing.expectError(expected_err, fs.makeDirAbsolute(invalid_path));
-                try testing.expectError(expected_err, fs.makeDirAbsoluteZ(invalid_path));
                 try testing.expectError(expected_err, fs.deleteDirAbsolute(invalid_path));
-                try testing.expectError(expected_err, fs.deleteDirAbsoluteZ(invalid_path));
                 try testing.expectError(expected_err, fs.renameAbsolute(invalid_path, invalid_path));
-                try testing.expectError(expected_err, fs.renameAbsoluteZ(invalid_path, invalid_path));
                 try testing.expectError(expected_err, fs.openDirAbsolute(invalid_path, .{}));
-                try testing.expectError(expected_err, fs.openDirAbsoluteZ(invalid_path, .{}));
                 try testing.expectError(expected_err, fs.openFileAbsolute(invalid_path, .{}));
-                try testing.expectError(expected_err, fs.openFileAbsoluteZ(invalid_path, .{}));
                 try testing.expectError(expected_err, fs.accessAbsolute(invalid_path, .{}));
-                try testing.expectError(expected_err, fs.accessAbsoluteZ(invalid_path, .{}));
                 try testing.expectError(expected_err, fs.createFileAbsolute(invalid_path, .{}));
-                try testing.expectError(expected_err, fs.createFileAbsoluteZ(invalid_path, .{}));
                 try testing.expectError(expected_err, fs.deleteFileAbsolute(invalid_path));
-                try testing.expectError(expected_err, fs.deleteFileAbsoluteZ(invalid_path));
                 try testing.expectError(expected_err, fs.deleteTreeAbsolute(invalid_path));
                 var readlink_buf: [fs.max_path_bytes]u8 = undefined;
                 try testing.expectError(expected_err, fs.readLinkAbsolute(invalid_path, &readlink_buf));
-                try testing.expectError(expected_err, fs.readLinkAbsoluteZ(invalid_path, &readlink_buf));
                 try testing.expectError(expected_err, fs.symLinkAbsolute(invalid_path, invalid_path, .{}));
-                try testing.expectError(expected_err, fs.symLinkAbsoluteZ(invalid_path, invalid_path, .{}));
                 try testing.expectError(expected_err, fs.realpathAlloc(testing.allocator, invalid_path));
             }
         }
diff --git a/lib/std/os.zig b/lib/std/os.zig
index b7122ca03b..7fe64290b1 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -201,36 +201,6 @@ pub fn getFdPath(fd: std.posix.fd_t, out_buffer: *[max_path_bytes]u8) std.posix.
     }
 }
 
-pub const FstatatError = error{
-    SystemResources,
-    AccessDenied,
-    NameTooLong,
-    FileNotFound,
-    InvalidUtf8,
-    Unexpected,
-};
-
-/// WASI-only. Same as `fstatat` but targeting WASI.
-/// `pathname` should be encoded as valid UTF-8.
-/// See also `fstatat`.
-pub fn fstatat_wasi(dirfd: posix.fd_t, pathname: []const u8, flags: wasi.lookupflags_t) FstatatError!wasi.filestat_t {
-    var stat: wasi.filestat_t = undefined;
-    switch (wasi.path_filestat_get(dirfd, flags, pathname.ptr, pathname.len, &stat)) {
-        .SUCCESS => return stat,
-        .INVAL => unreachable,
-        .BADF => unreachable, // Always a race condition.
-        .NOMEM => return error.SystemResources,
-        .ACCES => return error.AccessDenied,
-        .FAULT => unreachable,
-        .NAMETOOLONG => return error.NameTooLong,
-        .NOENT => return error.FileNotFound,
-        .NOTDIR => return error.FileNotFound,
-        .NOTCAPABLE => return error.AccessDenied,
-        .ILSEQ => return error.InvalidUtf8,
-        else => |err| return posix.unexpectedErrno(err),
-    }
-}
-
 pub fn fstat_wasi(fd: posix.fd_t) posix.FStatError!wasi.filestat_t {
     var stat: wasi.filestat_t = undefined;
     switch (wasi.fd_filestat_get(fd, &stat)) {
diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index cbf49638a3..f36effe380 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -146,7 +146,7 @@ pub fn OpenFile(sub_path_w: []const u16, options: OpenFileOptions) OpenError!HAN
                 // call has failed. There is not really a sane way to handle
                 // this other than retrying the creation after the OS finishes
                 // the deletion.
-                std.Thread.sleep(std.time.ns_per_ms);
+                kernel32.Sleep(1);
                 continue;
             },
             .VIRUS_INFECTED, .VIRUS_DELETED => return error.AntivirusInterference,
@@ -604,7 +604,7 @@ pub const ReadFileError = error{
     BrokenPipe,
     /// The specified network name is no longer available.
     ConnectionResetByPeer,
-    OperationAborted,
+    Canceled,
     /// Unable to read file due to lock.
     LockViolation,
     /// Known to be possible when:
@@ -654,7 +654,7 @@ pub fn ReadFile(in_hFile: HANDLE, buffer: []u8, offset: ?u64) ReadFileError!usiz
 
 pub const WriteFileError = error{
     SystemResources,
-    OperationAborted,
+    Canceled,
     BrokenPipe,
     NotOpenForWriting,
     /// The process cannot access the file because another process has locked
@@ -694,7 +694,7 @@ pub fn WriteFile(
         switch (GetLastError()) {
             .INVALID_USER_BUFFER => return error.SystemResources,
             .NOT_ENOUGH_MEMORY => return error.SystemResources,
-            .OPERATION_ABORTED => return error.OperationAborted,
+            .OPERATION_ABORTED => return error.Canceled,
             .NOT_ENOUGH_QUOTA => return error.SystemResources,
             .IO_PENDING => unreachable,
             .NO_DATA => return error.BrokenPipe,
diff --git a/lib/std/posix.zig b/lib/std/posix.zig
index b27468617c..651f6eb117 100644
--- a/lib/std/posix.zig
+++ b/lib/std/posix.zig
@@ -821,9 +821,6 @@ pub const ReadError = std.Io.File.ReadStreamingError;
 /// The corresponding POSIX limit is `maxInt(isize)`.
 pub fn read(fd: fd_t, buf: []u8) ReadError!usize {
     if (buf.len == 0) return 0;
-    if (native_os == .windows) {
-        return windows.ReadFile(fd, buf, null);
-    }
     if (native_os == .wasi and !builtin.link_libc) {
         const iovs = [1]iovec{iovec{
             .base = buf.ptr,
@@ -1181,7 +1178,7 @@ pub const WriteError = error{
     PermissionDenied,
     BrokenPipe,
     SystemResources,
-    OperationAborted,
+    Canceled,
     NotOpenForWriting,
 
     /// The process cannot access the file because another process has locked
@@ -1597,10 +1594,7 @@ pub fn openZ(file_path: [*:0]const u8, flags: O, perm: mode_t) OpenError!fd_t {
             .PERM => return error.PermissionDenied,
             .EXIST => return error.PathAlreadyExists,
             .BUSY => return error.DeviceBusy,
-            .ILSEQ => |err| if (native_os == .wasi)
-                return error.InvalidUtf8
-            else
-                return unexpectedErrno(err),
+            .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1678,7 +1672,7 @@ pub fn openatWasi(
             .EXIST => return error.PathAlreadyExists,
             .BUSY => return error.DeviceBusy,
             .NOTCAPABLE => return error.AccessDenied,
-            .ILSEQ => return error.InvalidUtf8,
+            .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1773,10 +1767,7 @@ pub fn openatZ(dir_fd: fd_t, file_path: [*:0]const u8, flags: O, mode: mode_t) O
             .AGAIN => return error.WouldBlock,
             .TXTBSY => return error.FileBusy,
             .NXIO => return error.NoDevice,
-            .ILSEQ => |err| if (native_os == .wasi)
-                return error.InvalidUtf8
-            else
-                return unexpectedErrno(err),
+            .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -2084,10 +2075,7 @@ pub fn symlinkZ(target_path: [*:0]const u8, sym_link_path: [*:0]const u8) SymLin
         .NOMEM => return error.SystemResources,
         .NOSPC => return error.NoSpaceLeft,
         .ROFS => return error.ReadOnlyFileSystem,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2133,7 +2121,7 @@ pub fn symlinkatWasi(target_path: []const u8, newdirfd: fd_t, sym_link_path: []c
         .NOSPC => return error.NoSpaceLeft,
         .ROFS => return error.ReadOnlyFileSystem,
         .NOTCAPABLE => return error.AccessDenied,
-        .ILSEQ => return error.InvalidUtf8,
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2162,10 +2150,7 @@ pub fn symlinkatZ(target_path: [*:0]const u8, newdirfd: fd_t, sym_link_path: [*:
         .NOMEM => return error.SystemResources,
         .NOSPC => return error.NoSpaceLeft,
         .ROFS => return error.ReadOnlyFileSystem,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2184,9 +2169,7 @@ pub const LinkError = UnexpectedError || error{
     NoSpaceLeft,
     ReadOnlyFileSystem,
     NotSameFileSystem,
-
-    /// WASI-only; file paths must be valid UTF-8.
-    InvalidUtf8,
+    BadPathName,
 };
 
 /// On WASI, both paths should be encoded as valid UTF-8.
@@ -2212,10 +2195,7 @@ pub fn linkZ(oldpath: [*:0]const u8, newpath: [*:0]const u8) LinkError!void {
         .ROFS => return error.ReadOnlyFileSystem,
         .XDEV => return error.NotSameFileSystem,
         .INVAL => unreachable,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2266,10 +2246,7 @@ pub fn linkatZ(
         .ROFS => return error.ReadOnlyFileSystem,
         .XDEV => return error.NotSameFileSystem,
         .INVAL => unreachable,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2315,7 +2292,7 @@ pub fn linkat(
             .ROFS => return error.ReadOnlyFileSystem,
             .XDEV => return error.NotSameFileSystem,
             .INVAL => unreachable,
-            .ILSEQ => return error.InvalidUtf8,
+            .ILSEQ => return error.BadPathName,
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -2398,10 +2375,7 @@ pub fn unlinkZ(file_path: [*:0]const u8) UnlinkError!void {
         .NOTDIR => return error.NotDir,
         .NOMEM => return error.SystemResources,
         .ROFS => return error.ReadOnlyFileSystem,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2460,7 +2434,7 @@ pub fn unlinkatWasi(dirfd: fd_t, file_path: []const u8, flags: u32) UnlinkatErro
         .ROFS => return error.ReadOnlyFileSystem,
         .NOTEMPTY => return error.DirNotEmpty,
         .NOTCAPABLE => return error.AccessDenied,
-        .ILSEQ => return error.InvalidUtf8,
+        .ILSEQ => return error.BadPathName,
 
         .INVAL => unreachable, // invalid flags, or pathname has . as last component
         .BADF => unreachable, // always a race condition
@@ -2493,10 +2467,7 @@ pub fn unlinkatZ(dirfd: fd_t, file_path_c: [*:0]const u8, flags: u32) UnlinkatEr
         .ROFS => return error.ReadOnlyFileSystem,
         .EXIST => return error.DirNotEmpty,
         .NOTEMPTY => return error.DirNotEmpty,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
 
         .INVAL => unreachable, // invalid flags, or pathname has . as last component
         .BADF => unreachable, // always a race condition
@@ -2598,10 +2569,7 @@ pub fn renameZ(old_path: [*:0]const u8, new_path: [*:0]const u8) RenameError!voi
         .NOTEMPTY => return error.PathAlreadyExists,
         .ROFS => return error.ReadOnlyFileSystem,
         .XDEV => return error.RenameAcrossMountPoints,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2662,7 +2630,7 @@ fn renameatWasi(old: RelativePathWasi, new: RelativePathWasi) RenameError!void {
         .ROFS => return error.ReadOnlyFileSystem,
         .XDEV => return error.RenameAcrossMountPoints,
         .NOTCAPABLE => return error.AccessDenied,
-        .ILSEQ => return error.InvalidUtf8,
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2713,10 +2681,7 @@ pub fn renameatZ(
         .NOTEMPTY => return error.PathAlreadyExists,
         .ROFS => return error.ReadOnlyFileSystem,
         .XDEV => return error.RenameAcrossMountPoints,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2870,7 +2835,7 @@ pub fn mkdiratWasi(dir_fd: fd_t, sub_dir_path: []const u8, mode: mode_t) MakeDir
         .NOTDIR => return error.NotDir,
         .ROFS => return error.ReadOnlyFileSystem,
         .NOTCAPABLE => return error.AccessDenied,
-        .ILSEQ => return error.InvalidUtf8,
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2901,10 +2866,7 @@ pub fn mkdiratZ(dir_fd: fd_t, sub_dir_path: [*:0]const u8, mode: mode_t) MakeDir
         .ROFS => return error.ReadOnlyFileSystem,
         // dragonfly: when dir_fd is unlinked from filesystem
         .NOTCONN => return error.FileNotFound,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -2973,10 +2935,7 @@ pub fn mkdirZ(dir_path: [*:0]const u8, mode: mode_t) MakeDirError!void {
         .NOSPC => return error.NoSpaceLeft,
         .NOTDIR => return error.NotDir,
         .ROFS => return error.ReadOnlyFileSystem,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3067,10 +3026,7 @@ pub fn rmdirZ(dir_path: [*:0]const u8) DeleteDirError!void {
         .EXIST => return error.DirNotEmpty,
         .NOTEMPTY => return error.DirNotEmpty,
         .ROFS => return error.ReadOnlyFileSystem,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3145,10 +3101,7 @@ pub fn chdirZ(dir_path: [*:0]const u8) ChangeCurDirError!void {
         .NOENT => return error.FileNotFound,
         .NOMEM => return error.SystemResources,
         .NOTDIR => return error.NotDir,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3254,10 +3207,7 @@ pub fn readlinkZ(file_path: [*:0]const u8, out_buffer: []u8) ReadLinkError![]u8
         .NOENT => return error.FileNotFound,
         .NOMEM => return error.SystemResources,
         .NOTDIR => return error.NotDir,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3299,7 +3249,7 @@ pub fn readlinkatWasi(dirfd: fd_t, file_path: []const u8, out_buffer: []u8) Read
         .NOMEM => return error.SystemResources,
         .NOTDIR => return error.NotDir,
         .NOTCAPABLE => return error.AccessDenied,
-        .ILSEQ => return error.InvalidUtf8,
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -3332,10 +3282,7 @@ pub fn readlinkatZ(dirfd: fd_t, file_path: [*:0]const u8, out_buffer: []u8) Read
         .NOENT => return error.FileNotFound,
         .NOMEM => return error.SystemResources,
         .NOTDIR => return error.NotDir,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4421,13 +4368,10 @@ pub const FStatAtError = FStatError || error{
 /// which is relative to `dirfd` handle.
 /// On WASI, `pathname` should be encoded as valid UTF-8.
 /// On other platforms, `pathname` is an opaque sequence of bytes with no particular encoding.
-/// See also `fstatatZ` and `std.os.fstatat_wasi`.
+/// See also `fstatatZ`.
 pub fn fstatat(dirfd: fd_t, pathname: []const u8, flags: u32) FStatAtError!Stat {
     if (native_os == .wasi and !builtin.link_libc) {
-        const filestat = try std.os.fstatat_wasi(dirfd, pathname, .{
-            .SYMLINK_FOLLOW = (flags & AT.SYMLINK_NOFOLLOW) == 0,
-        });
-        return Stat.fromFilestat(filestat);
+        @compileError("use std.Io instead");
     } else if (native_os == .windows) {
         @compileError("fstatat is not yet implemented on Windows");
     } else {
@@ -4440,10 +4384,7 @@ pub fn fstatat(dirfd: fd_t, pathname: []const u8, flags: u32) FStatAtError!Stat
 /// See also `fstatat`.
 pub fn fstatatZ(dirfd: fd_t, pathname: [*:0]const u8, flags: u32) FStatAtError!Stat {
     if (native_os == .wasi and !builtin.link_libc) {
-        const filestat = try std.os.fstatat_wasi(dirfd, mem.sliceTo(pathname, 0), .{
-            .SYMLINK_FOLLOW = (flags & AT.SYMLINK_NOFOLLOW) == 0,
-        });
-        return Stat.fromFilestat(filestat);
+        @compileError("use std.Io instead");
     }
 
     const fstatat_sym = if (lfs64_abi) system.fstatat64 else system.fstatat;
@@ -4460,10 +4401,7 @@ pub fn fstatatZ(dirfd: fd_t, pathname: [*:0]const u8, flags: u32) FStatAtError!S
         .LOOP => return error.SymLinkLoop,
         .NOENT => return error.FileNotFound,
         .NOTDIR => return error.FileNotFound,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -4991,10 +4929,7 @@ pub fn accessZ(path: [*:0]const u8, mode: u32) AccessError!void {
         .FAULT => unreachable,
         .IO => return error.InputOutput,
         .NOMEM => return error.SystemResources,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
@@ -5072,10 +5007,7 @@ pub fn faccessatZ(dirfd: fd_t, path: [*:0]const u8, mode: u32, flags: u32) Acces
         .FAULT => unreachable,
         .IO => return error.InputOutput,
         .NOMEM => return error.SystemResources,
-        .ILSEQ => |err| if (native_os == .wasi)
-            return error.InvalidUtf8
-        else
-            return unexpectedErrno(err),
+        .ILSEQ => return error.BadPathName,
         else => |err| return unexpectedErrno(err),
     }
 }
diff --git a/lib/std/posix/test.zig b/lib/std/posix/test.zig
index b5ce476441..230440a2f1 100644
--- a/lib/std/posix/test.zig
+++ b/lib/std/posix/test.zig
@@ -226,49 +226,6 @@ test "linkat with different directories" {
     }
 }
 
-test "fstatat" {
-    if ((builtin.cpu.arch == .riscv32 or builtin.cpu.arch.isLoongArch()) and builtin.os.tag == .linux and !builtin.link_libc) return error.SkipZigTest; // No `fstatat()`.
-    // enable when `fstat` and `fstatat` are implemented on Windows
-    if (native_os == .windows) return error.SkipZigTest;
-
-    var tmp = tmpDir(.{});
-    defer tmp.cleanup();
-
-    // create dummy file
-    const contents = "nonsense";
-    try tmp.dir.writeFile(.{ .sub_path = "file.txt", .data = contents });
-
-    // fetch file's info on the opened fd directly
-    const file = try tmp.dir.openFile("file.txt", .{});
-    const stat = try posix.fstat(file.handle);
-    defer file.close();
-
-    // now repeat but using `fstatat` instead
-    const statat = try posix.fstatat(tmp.dir.fd, "file.txt", posix.AT.SYMLINK_NOFOLLOW);
-
-    try expectEqual(stat.dev, statat.dev);
-    try expectEqual(stat.ino, statat.ino);
-    try expectEqual(stat.nlink, statat.nlink);
-    try expectEqual(stat.mode, statat.mode);
-    try expectEqual(stat.uid, statat.uid);
-    try expectEqual(stat.gid, statat.gid);
-    try expectEqual(stat.rdev, statat.rdev);
-    try expectEqual(stat.size, statat.size);
-    try expectEqual(stat.blksize, statat.blksize);
-
-    // The stat.blocks/statat.blocks count is managed by the filesystem and may
-    // change if the file is stored in a journal or "inline".
-    // try expectEqual(stat.blocks, statat.blocks);
-
-    // s390x-linux does not have nanosecond precision for fstat(), but it does for
-    // fstatat(). As a result, comparing the timestamps isn't worth the effort
-    if (!(builtin.cpu.arch == .s390x and builtin.os.tag == .linux)) {
-        try expectEqual(stat.atime(), statat.atime());
-        try expectEqual(stat.mtime(), statat.mtime());
-        try expectEqual(stat.ctime(), statat.ctime());
-    }
-}
-
 test "readlinkat" {
     var tmp = tmpDir(.{});
     defer tmp.cleanup();
diff --git a/test/src/convert-stack-trace.zig b/test/src/convert-stack-trace.zig
index c7cd01a460..91be53a8e5 100644
--- a/test/src/convert-stack-trace.zig
+++ b/test/src/convert-stack-trace.zig
@@ -32,6 +32,12 @@ pub fn main() !void {
     const args = try std.process.argsAlloc(arena);
     if (args.len != 2) std.process.fatal("usage: convert-stack-trace path/to/test/output", .{});
 
+    const gpa = arena;
+
+    var threaded: std.Io.Threaded = .init(gpa);
+    defer threaded.deinit();
+    const io = threaded.io();
+
     var read_buf: [1024]u8 = undefined;
     var write_buf: [1024]u8 = undefined;
 
@@ -40,7 +46,7 @@ pub fn main() !void {
 
     const out_file: std.fs.File = .stdout();
 
-    var in_fr = in_file.reader(&read_buf);
+    var in_fr = in_file.reader(io, &read_buf);
     var out_fw = out_file.writer(&write_buf);
 
     const w = &out_fw.interface;
diff --git a/tools/docgen.zig b/tools/docgen.zig
index 18311b0d54..d23892e06c 100644
--- a/tools/docgen.zig
+++ b/tools/docgen.zig
@@ -36,6 +36,12 @@ pub fn main() !void {
     var args_it = try process.argsWithAllocator(arena);
     if (!args_it.skip()) @panic("expected self arg");
 
+    const gpa = arena;
+
+    var threaded: std.Io.Threaded = .init(gpa);
+    defer threaded.deinit();
+    const io = threaded.io();
+
     var opt_code_dir: ?[]const u8 = null;
     var opt_input: ?[]const u8 = null;
     var opt_output: ?[]const u8 = null;
@@ -77,7 +83,7 @@ pub fn main() !void {
     var code_dir = try fs.cwd().openDir(code_dir_path, .{});
     defer code_dir.close();
 
-    var in_file_reader = in_file.reader(&.{});
+    var in_file_reader = in_file.reader(io, &.{});
     const input_file_bytes = try in_file_reader.interface.allocRemaining(arena, .limited(max_doc_file_size));
 
     var tokenizer = Tokenizer.init(input_path, input_file_bytes);
diff --git a/tools/doctest.zig b/tools/doctest.zig
index ccdbc6b065..de8d3a80ee 100644
--- a/tools/doctest.zig
+++ b/tools/doctest.zig
@@ -1,5 +1,8 @@
 const builtin = @import("builtin");
+
 const std = @import("std");
+const Io = std.Io;
+const Writer = std.Io.Writer;
 const fatal = std.process.fatal;
 const mem = std.mem;
 const fs = std.fs;
@@ -7,7 +10,6 @@ const process = std.process;
 const Allocator = std.mem.Allocator;
 const testing = std.testing;
 const getExternalExecutor = std.zig.system.getExternalExecutor;
-const Writer = std.Io.Writer;
 
 const max_doc_file_size = 10 * 1024 * 1024;
 
@@ -36,6 +38,12 @@ pub fn main() !void {
     var args_it = try process.argsWithAllocator(arena);
     if (!args_it.skip()) fatal("missing argv[0]", .{});
 
+    const gpa = arena;
+
+    var threaded: std.Io.Threaded = .init(gpa);
+    defer threaded.deinit();
+    const io = threaded.io();
+
     var opt_input: ?[]const u8 = null;
     var opt_output: ?[]const u8 = null;
     var opt_zig: ?[]const u8 = null;
@@ -93,6 +101,7 @@ pub fn main() !void {
     try printSourceBlock(arena, out, source, fs.path.basename(input_path));
     try printOutput(
         arena,
+        io,
         out,
         code,
         tmp_dir_path,
@@ -109,6 +118,7 @@ pub fn main() !void {
 
 fn printOutput(
     arena: Allocator,
+    io: Io,
     out: *Writer,
     code: Code,
     /// Relative to this process' cwd.
@@ -123,11 +133,11 @@ fn printOutput(
     var env_map = try process.getEnvMap(arena);
     try env_map.put("CLICOLOR_FORCE", "1");
 
-    const host = try std.zig.system.resolveTargetQuery(.{});
+    const host = try std.zig.system.resolveTargetQuery(io, .{});
     const obj_ext = builtin.object_format.fileExt(builtin.cpu.arch);
     const print = std.debug.print;
 
-    var shell_buffer: std.Io.Writer.Allocating = .init(arena);
+    var shell_buffer: Writer.Allocating = .init(arena);
     defer shell_buffer.deinit();
     const shell_out = &shell_buffer.writer;
 
@@ -238,7 +248,7 @@ fn printOutput(
             const target_query = try std.Target.Query.parse(.{
                 .arch_os_abi = code.target_str orelse "native",
             });
-            const target = try std.zig.system.resolveTargetQuery(target_query);
+            const target = try std.zig.system.resolveTargetQuery(io, target_query);
 
             const path_to_exe = try std.fmt.allocPrint(arena, "./{s}{s}", .{
                 code_name, target.exeFileExt(),
@@ -316,9 +326,7 @@ fn printOutput(
                 const target_query = try std.Target.Query.parse(.{
                     .arch_os_abi = triple,
                 });
-                const target = try std.zig.system.resolveTargetQuery(
-                    target_query,
-                );
+                const target = try std.zig.system.resolveTargetQuery(io, target_query);
                 switch (getExternalExecutor(&host, &target, .{
                     .link_libc = code.link_libc,
                 })) {
@@ -1397,7 +1405,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1414,7 +1422,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1428,7 +1436,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1447,7 +1455,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1468,7 +1476,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1487,7 +1495,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1510,7 +1518,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1532,7 +1540,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1549,7 +1557,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1568,7 +1576,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);
@@ -1583,7 +1591,7 @@ test "printShell" {
             \\</samp></pre></figure>
         ;
 
-        var buffer: std.Io.Writer.Allocating = .init(test_allocator);
+        var buffer: Writer.Allocating = .init(test_allocator);
         defer buffer.deinit();
 
         try printShell(&buffer.writer, shell_out, false);