diff --git a/lib/compiler/test_runner.zig b/lib/compiler/test_runner.zig
index 0d6f451947..fbf37f7ec9 100644
--- a/lib/compiler/test_runner.zig
+++ b/lib/compiler/test_runner.zig
@@ -148,7 +148,7 @@ fn mainServer() !void {
                     error.SkipZigTest => .skip,
                     else => s: {
                         if (@errorReturnTrace()) |trace| {
-                            std.debug.dumpStackTrace(trace);
+                            std.debug.dumpStackTrace(trace.*);
                         }
                         break :s .fail;
                     },
@@ -269,7 +269,7 @@ fn mainTerminal() void {
                     std.debug.print("FAIL ({t})\n", .{err});
                 }
                 if (@errorReturnTrace()) |trace| {
-                    std.debug.dumpStackTrace(trace);
+                    std.debug.dumpStackTrace(trace.*);
                 }
                 test_node.end();
             },
diff --git a/lib/std/Build/Step.zig b/lib/std/Build/Step.zig
index aa922ff37b..d1985739bd 100644
--- a/lib/std/Build/Step.zig
+++ b/lib/std/Build/Step.zig
@@ -332,7 +332,7 @@ pub fn cast(step: *Step, comptime T: type) ?*T {
 pub fn dump(step: *Step, w: *Io.Writer, tty_config: Io.tty.Config) void {
     if (step.debug_stack_trace.instruction_addresses.len > 0) {
         w.print("name: '{s}'. creation stack trace:\n", .{step.name}) catch {};
-        std.debug.writeStackTrace(&step.debug_stack_trace, w, tty_config) catch {};
+        std.debug.writeStackTrace(step.debug_stack_trace, w, tty_config) catch {};
     } else {
         const field = "debug_stack_frames_count";
         comptime assert(@hasField(Build, field));
diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 330cc6725d..18e6e72563 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -31,7 +31,7 @@ const max_iovecs_len = 8;
 const splat_buffer_size = 64;
 
 comptime {
-    assert(max_iovecs_len <= posix.IOV_MAX);
+    if (@TypeOf(posix.IOV_MAX) != void) assert(max_iovecs_len <= posix.IOV_MAX);
 }
 
 const Closure = struct {
@@ -91,9 +91,7 @@ pub fn init(
 
 /// Statically initialize such that any call to the following functions will
 /// fail with `error.OutOfMemory`:
-/// * `Io.VTable.async`
 /// * `Io.VTable.concurrent`
-/// * `Io.VTable.groupAsync`
 /// When initialized this way, `deinit` is safe, but unnecessary to call.
 pub const init_single_threaded: Threaded = .{
     .allocator = .failing,
diff --git a/lib/std/Io/net/HostName.zig b/lib/std/Io/net/HostName.zig
index 376f798e3e..ea1ffc4834 100644
--- a/lib/std/Io/net/HostName.zig
+++ b/lib/std/Io/net/HostName.zig
@@ -221,7 +221,7 @@ pub fn connect(
     defer {
         connect_many.cancel(io);
         if (!saw_end) while (true) switch (connect_many_queue.getOneUncancelable(io)) {
-            .connection => |loser| if (loser) |s| s.closeConst(io) else |_| continue,
+            .connection => |loser| if (loser) |s| s.close(io) else |_| continue,
             .end => break,
         };
     }
diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index b5f950a08a..891c4f220e 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -577,7 +577,7 @@ fn callFn(comptime f: anytype, args: anytype) switch (Impl) {
                     @call(.auto, f, args) catch |err| {
                         std.debug.print("error: {s}\n", .{@errorName(err)});
                         if (@errorReturnTrace()) |trace| {
-                            std.debug.dumpStackTrace(trace);
+                            std.debug.dumpStackTrace(trace.*);
                         }
                     };
 
diff --git a/lib/std/builtin.zig b/lib/std/builtin.zig
index c0be44b939..8f974161f8 100644
--- a/lib/std/builtin.zig
+++ b/lib/std/builtin.zig
@@ -37,19 +37,6 @@ pub const subsystem: ?std.Target.SubSystem = blk: {
 pub const StackTrace = struct {
     index: usize,
     instruction_addresses: []usize,
-
-    pub fn format(st: *const StackTrace, writer: *std.Io.Writer) std.Io.Writer.Error!void {
-        // TODO: re-evaluate whether to use format() methods at all.
-        // Until then, avoid an error when using GeneralPurposeAllocator with WebAssembly
-        // where it tries to call detectTTYConfig here.
-        if (builtin.os.tag == .freestanding) return;
-
-        // TODO: why on earth are we using stderr's ttyconfig?
-        // If we want colored output, we should just make a formatter out of `writeStackTrace`.
-        const tty_config = std.Io.tty.detectConfig(.stderr());
-        try writer.writeAll("\n");
-        try std.debug.writeStackTrace(st, writer, tty_config);
-    }
 };
 
 /// This data structure is used by the Zig language code generation and
diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 7e09bfec8a..3d88123c64 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -1,4 +1,7 @@
 const std = @import("std.zig");
+const Io = std.Io;
+const Writer = std.Io.Writer;
+const tty = std.Io.tty;
 const math = std.math;
 const mem = std.mem;
 const posix = std.posix;
@@ -7,12 +10,11 @@ const testing = std.testing;
 const Allocator = mem.Allocator;
 const File = std.fs.File;
 const windows = std.os.windows;
-const Writer = std.Io.Writer;
-const tty = std.Io.tty;
 
 const builtin = @import("builtin");
 const native_arch = builtin.cpu.arch;
 const native_os = builtin.os.tag;
+const StackTrace = std.builtin.StackTrace;
 
 const root = @import("root");
 
@@ -545,13 +547,13 @@ pub fn defaultPanic(
                     stderr.print("panic: ", .{}) catch break :trace;
                 } else {
                     const current_thread_id = std.Thread.getCurrentId();
-                    stderr.print("thread {} panic: ", .{current_thread_id}) catch break :trace;
+                    stderr.print("thread {d} panic: ", .{current_thread_id}) catch break :trace;
                 }
                 stderr.print("{s}\n", .{msg}) catch break :trace;
 
                 if (@errorReturnTrace()) |t| if (t.index > 0) {
                     stderr.writeAll("error return context:\n") catch break :trace;
-                    writeStackTrace(t, stderr, tty_config) catch break :trace;
+                    writeStackTrace(t.*, stderr, tty_config) catch break :trace;
                     stderr.writeAll("\nstack trace:\n") catch break :trace;
                 };
                 writeCurrentStackTrace(.{
@@ -607,8 +609,8 @@ pub const StackUnwindOptions = struct {
 /// the given buffer, so `addr_buf` must have a lifetime at least equal to the `StackTrace`.
 ///
 /// See `writeCurrentStackTrace` to immediately print the trace instead of capturing it.
-pub noinline fn captureCurrentStackTrace(options: StackUnwindOptions, addr_buf: []usize) std.builtin.StackTrace {
-    const empty_trace: std.builtin.StackTrace = .{ .index = 0, .instruction_addresses = &.{} };
+pub noinline fn captureCurrentStackTrace(options: StackUnwindOptions, addr_buf: []usize) StackTrace {
+    const empty_trace: StackTrace = .{ .index = 0, .instruction_addresses = &.{} };
     if (!std.options.allow_stack_tracing) return empty_trace;
     var it = StackIterator.init(options.context) catch return empty_trace;
     defer it.deinit();
@@ -646,6 +648,9 @@ pub noinline fn captureCurrentStackTrace(options: StackUnwindOptions, addr_buf:
 ///
 /// See `captureCurrentStackTrace` to capture the trace addresses into a buffer instead of printing.
 pub noinline fn writeCurrentStackTrace(options: StackUnwindOptions, writer: *Writer, tty_config: tty.Config) Writer.Error!void {
+    var threaded: Io.Threaded = .init_single_threaded;
+    const io = threaded.io();
+
     if (!std.options.allow_stack_tracing) {
         tty_config.setColor(writer, .dim) catch {};
         try writer.print("Cannot print stack trace: stack tracing is disabled\n", .{});
@@ -730,7 +735,7 @@ pub noinline fn writeCurrentStackTrace(options: StackUnwindOptions, writer: *Wri
             }
             // `ret_addr` is the return address, which is *after* the function call.
             // Subtract 1 to get an address *in* the function call for a better source location.
-            try printSourceAtAddress(di_gpa, di, writer, ret_addr -| StackIterator.ra_call_offset, tty_config);
+            try printSourceAtAddress(di_gpa, io, di, writer, ret_addr -| StackIterator.ra_call_offset, tty_config);
             printed_any_frame = true;
         },
     };
@@ -754,14 +759,29 @@ pub fn dumpCurrentStackTrace(options: StackUnwindOptions) void {
     };
 }
 
+pub const FormatStackTrace = struct {
+    stack_trace: StackTrace,
+    tty_config: tty.Config,
+
+    pub fn format(context: @This(), writer: *Io.Writer) Io.Writer.Error!void {
+        try writer.writeAll("\n");
+        try writeStackTrace(context.stack_trace, writer, context.tty_config);
+    }
+};
+
 /// Write a previously captured stack trace to `writer`, annotated with source locations.
-pub fn writeStackTrace(st: *const std.builtin.StackTrace, writer: *Writer, tty_config: tty.Config) Writer.Error!void {
+pub fn writeStackTrace(st: StackTrace, writer: *Writer, tty_config: tty.Config) Writer.Error!void {
     if (!std.options.allow_stack_tracing) {
         tty_config.setColor(writer, .dim) catch {};
         try writer.print("Cannot print stack trace: stack tracing is disabled\n", .{});
         tty_config.setColor(writer, .reset) catch {};
         return;
     }
+    // We use an independent Io implementation here in case there was a problem
+    // with the application's Io implementation itself.
+    var threaded: Io.Threaded = .init_single_threaded;
+    const io = threaded.io();
+
     // Fetch `st.index` straight away. Aside from avoiding redundant loads, this prevents issues if
     // `st` is `@errorReturnTrace()` and errors are encountered while writing the stack trace.
     const n_frames = st.index;
@@ -779,7 +799,7 @@ pub fn writeStackTrace(st: *const std.builtin.StackTrace, writer: *Writer, tty_c
     for (st.instruction_addresses[0..captured_frames]) |ret_addr| {
         // `ret_addr` is the return address, which is *after* the function call.
         // Subtract 1 to get an address *in* the function call for a better source location.
-        try printSourceAtAddress(di_gpa, di, writer, ret_addr -| StackIterator.ra_call_offset, tty_config);
+        try printSourceAtAddress(di_gpa, io, di, writer, ret_addr -| StackIterator.ra_call_offset, tty_config);
     }
     if (n_frames > captured_frames) {
         tty_config.setColor(writer, .bold) catch {};
@@ -788,7 +808,7 @@ pub fn writeStackTrace(st: *const std.builtin.StackTrace, writer: *Writer, tty_c
     }
 }
 /// A thin wrapper around `writeStackTrace` which writes to stderr and ignores write errors.
-pub fn dumpStackTrace(st: *const std.builtin.StackTrace) void {
+pub fn dumpStackTrace(st: StackTrace) void {
     const tty_config = tty.detectConfig(.stderr());
     const stderr = lockStderrWriter(&.{});
     defer unlockStderrWriter();
@@ -1075,8 +1095,8 @@ pub inline fn stripInstructionPtrAuthCode(ptr: usize) usize {
     return ptr;
 }
 
-fn printSourceAtAddress(gpa: Allocator, debug_info: *SelfInfo, writer: *Writer, address: usize, tty_config: tty.Config) Writer.Error!void {
-    const symbol: Symbol = debug_info.getSymbol(gpa, address) catch |err| switch (err) {
+fn printSourceAtAddress(gpa: Allocator, io: Io, debug_info: *SelfInfo, writer: *Writer, address: usize, tty_config: tty.Config) Writer.Error!void {
+    const symbol: Symbol = debug_info.getSymbol(gpa, io, address) catch |err| switch (err) {
         error.MissingDebugInfo,
         error.UnsupportedDebugInfo,
         error.InvalidDebugInfo,
@@ -1581,11 +1601,14 @@ test "manage resources correctly" {
         }
     };
     const gpa = std.testing.allocator;
-    var discarding: std.Io.Writer.Discarding = .init(&.{});
+    var threaded: Io.Threaded = .init_single_threaded;
+    const io = threaded.io();
+    var discarding: Io.Writer.Discarding = .init(&.{});
     var di: SelfInfo = .init;
     defer di.deinit(gpa);
     try printSourceAtAddress(
         gpa,
+        io,
         &di,
         &discarding.writer,
         S.showMyTrace(),
@@ -1659,11 +1682,11 @@ pub fn ConfigurableTrace(comptime size: usize, comptime stack_frame_count: usize
                 stderr.print("{s}:\n", .{t.notes[i]}) catch return;
                 var frames_array_mutable = frames_array;
                 const frames = mem.sliceTo(frames_array_mutable[0..], 0);
-                const stack_trace: std.builtin.StackTrace = .{
+                const stack_trace: StackTrace = .{
                     .index = frames.len,
                     .instruction_addresses = frames,
                 };
-                writeStackTrace(&stack_trace, stderr, tty_config) catch return;
+                writeStackTrace(stack_trace, stderr, tty_config) catch return;
             }
             if (t.index > end) {
                 stderr.print("{d} more traces not shown; consider increasing trace size\n", .{
diff --git a/lib/std/debug/SelfInfo/MachO.zig b/lib/std/debug/SelfInfo/MachO.zig
index 8a0d9f0e1d..f7eb4465c5 100644
--- a/lib/std/debug/SelfInfo/MachO.zig
+++ b/lib/std/debug/SelfInfo/MachO.zig
@@ -30,7 +30,8 @@ pub fn deinit(si: *SelfInfo, gpa: Allocator) void {
     si.ofiles.deinit(gpa);
 }
 
-pub fn getSymbol(si: *SelfInfo, gpa: Allocator, address: usize) Error!std.debug.Symbol {
+pub fn getSymbol(si: *SelfInfo, gpa: Allocator, io: Io, address: usize) Error!std.debug.Symbol {
+    _ = io;
     const module = try si.findModule(gpa, address);
     defer si.mutex.unlock();
 
@@ -970,6 +971,7 @@ fn loadOFile(gpa: Allocator, o_file_path: []const u8) !OFile {
 }
 
 const std = @import("std");
+const Io = std.Io;
 const Allocator = std.mem.Allocator;
 const Dwarf = std.debug.Dwarf;
 const Error = std.debug.SelfInfoError;
diff --git a/lib/std/debug/SelfInfo/Windows.zig b/lib/std/debug/SelfInfo/Windows.zig
index 324b597d97..a0b26f8ec5 100644
--- a/lib/std/debug/SelfInfo/Windows.zig
+++ b/lib/std/debug/SelfInfo/Windows.zig
@@ -474,7 +474,7 @@ const Module = struct {
             break :pdb pdb;
         };
         errdefer if (opt_pdb) |*pdb| {
-            pdb.file_reader.file.close();
+            pdb.file_reader.file.close(io);
             pdb.deinit();
         };
 
@@ -484,6 +484,7 @@ const Module = struct {
 
         return .{
             .arena = arena_instance.state,
+            .io = io,
             .coff_image_base = coff_image_base,
             .mapped_file = mapped_file,
             .dwarf = opt_dwarf,
diff --git a/lib/std/fs/Dir.zig b/lib/std/fs/Dir.zig
index c4cbaf7196..aa1180a90d 100644
--- a/lib/std/fs/Dir.zig
+++ b/lib/std/fs/Dir.zig
@@ -1062,7 +1062,7 @@ pub fn makeOpenPath(self: Dir, sub_path: []const u8, open_dir_options: OpenOptio
                 w.SYNCHRONIZE | w.FILE_TRAVERSE |
                 (if (open_dir_options.iterate) w.FILE_LIST_DIRECTORY else @as(u32, 0));
 
-            return self.makeOpenPathAccessMaskW(sub_path, base_flags, open_dir_options.no_follow);
+            return self.makeOpenPathAccessMaskW(sub_path, base_flags, !open_dir_options.follow_symlinks);
         },
         else => {
             return self.openDir(sub_path, open_dir_options) catch |err| switch (err) {
@@ -1575,8 +1575,7 @@ pub fn symLink(
         // when converting to an NT namespaced path. CreateSymbolicLink in
         // symLinkW will handle the necessary conversion.
         var target_path_w: windows.PathSpace = undefined;
-        try windows.checkWtf8ToWtf16LeOverflow(target_path, &target_path_w.data);
-        target_path_w.len = try std.unicode.wtf8ToWtf16Le(&target_path_w.data, target_path);
+        target_path_w.len = try windows.wtf8ToWtf16Le(&target_path_w.data, target_path);
         target_path_w.data[target_path_w.len] = 0;
         // However, we need to canonicalize any path separators to `\`, since if
         // the target path is relative, then it must use `\` as the path separator.
diff --git a/lib/std/fs/File.zig b/lib/std/fs/File.zig
index ca3fb47a5a..ba0f29fd87 100644
--- a/lib/std/fs/File.zig
+++ b/lib/std/fs/File.zig
@@ -564,8 +564,8 @@ pub fn updateTimes(
     mtime: Io.Timestamp,
 ) UpdateTimesError!void {
     if (builtin.os.tag == .windows) {
-        const atime_ft = windows.nanoSecondsToFileTime(atime.nanoseconds);
-        const mtime_ft = windows.nanoSecondsToFileTime(mtime.nanoseconds);
+        const atime_ft = windows.nanoSecondsToFileTime(atime);
+        const mtime_ft = windows.nanoSecondsToFileTime(mtime);
         return windows.SetFileTime(self.handle, null, &atime_ft, &mtime_ft);
     }
     const times = [2]posix.timespec{
diff --git a/lib/std/heap/debug_allocator.zig b/lib/std/heap/debug_allocator.zig
index 8e66f722c3..4480009781 100644
--- a/lib/std/heap/debug_allocator.zig
+++ b/lib/std/heap/debug_allocator.zig
@@ -80,15 +80,15 @@
 //!
 //! Resizing and remapping are forwarded directly to the backing allocator,
 //! except where such operations would change the category from large to small.
+const builtin = @import("builtin");
+const StackTrace = std.builtin.StackTrace;
 
 const std = @import("std");
-const builtin = @import("builtin");
 const log = std.log.scoped(.gpa);
 const math = std.math;
 const assert = std.debug.assert;
 const mem = std.mem;
 const Allocator = std.mem.Allocator;
-const StackTrace = std.builtin.StackTrace;
 
 const default_page_size: usize = switch (builtin.os.tag) {
     // Makes `std.heap.PageAllocator` take the happy path.
@@ -421,7 +421,12 @@ pub fn DebugAllocator(comptime config: Config) type {
             return usedBitsCount(slot_count) * @sizeOf(usize);
         }
 
-        fn detectLeaksInBucket(bucket: *BucketHeader, size_class_index: usize, used_bits_count: usize) usize {
+        fn detectLeaksInBucket(
+            bucket: *BucketHeader,
+            size_class_index: usize,
+            used_bits_count: usize,
+            tty_config: std.Io.tty.Config,
+        ) usize {
             const size_class = @as(usize, 1) << @as(Log2USize, @intCast(size_class_index));
             const slot_count = slot_counts[size_class_index];
             var leaks: usize = 0;
@@ -436,7 +441,13 @@ pub fn DebugAllocator(comptime config: Config) type {
                             const stack_trace = bucketStackTrace(bucket, slot_count, slot_index, .alloc);
                             const page_addr = @intFromPtr(bucket) & ~(page_size - 1);
                             const addr = page_addr + slot_index * size_class;
-                            log.err("memory address 0x{x} leaked: {f}", .{ addr, stack_trace });
+                            log.err("memory address 0x{x} leaked: {f}", .{
+                                addr,
+                                std.debug.FormatStackTrace{
+                                    .stack_trace = stack_trace,
+                                    .tty_config = tty_config,
+                                },
+                            });
                             leaks += 1;
                         }
                     }
@@ -449,12 +460,14 @@ pub fn DebugAllocator(comptime config: Config) type {
         pub fn detectLeaks(self: *Self) usize {
             var leaks: usize = 0;
 
+            const tty_config = std.Io.tty.detectConfig(.stderr());
+
             for (self.buckets, 0..) |init_optional_bucket, size_class_index| {
                 var optional_bucket = init_optional_bucket;
                 const slot_count = slot_counts[size_class_index];
                 const used_bits_count = usedBitsCount(slot_count);
                 while (optional_bucket) |bucket| {
-                    leaks += detectLeaksInBucket(bucket, size_class_index, used_bits_count);
+                    leaks += detectLeaksInBucket(bucket, size_class_index, used_bits_count, tty_config);
                     optional_bucket = bucket.prev;
                 }
             }
@@ -464,7 +477,11 @@ pub fn DebugAllocator(comptime config: Config) type {
                 if (config.retain_metadata and large_alloc.freed) continue;
                 const stack_trace = large_alloc.getStackTrace(.alloc);
                 log.err("memory address 0x{x} leaked: {f}", .{
-                    @intFromPtr(large_alloc.bytes.ptr), stack_trace,
+                    @intFromPtr(large_alloc.bytes.ptr),
+                    std.debug.FormatStackTrace{
+                        .stack_trace = stack_trace,
+                        .tty_config = tty_config,
+                    },
                 });
                 leaks += 1;
             }
@@ -519,8 +536,20 @@ pub fn DebugAllocator(comptime config: Config) type {
         fn reportDoubleFree(ret_addr: usize, alloc_stack_trace: StackTrace, free_stack_trace: StackTrace) void {
             var addr_buf: [stack_n]usize = undefined;
             const second_free_stack_trace = std.debug.captureCurrentStackTrace(.{ .first_address = ret_addr }, &addr_buf);
+            const tty_config = std.Io.tty.detectConfig(.stderr());
             log.err("Double free detected. Allocation: {f} First free: {f} Second free: {f}", .{
-                alloc_stack_trace, free_stack_trace, second_free_stack_trace,
+                std.debug.FormatStackTrace{
+                    .stack_trace = alloc_stack_trace,
+                    .tty_config = tty_config,
+                },
+                std.debug.FormatStackTrace{
+                    .stack_trace = free_stack_trace,
+                    .tty_config = tty_config,
+                },
+                std.debug.FormatStackTrace{
+                    .stack_trace = second_free_stack_trace,
+                    .tty_config = tty_config,
+                },
             });
         }
 
@@ -561,11 +590,18 @@ pub fn DebugAllocator(comptime config: Config) type {
             if (config.safety and old_mem.len != entry.value_ptr.bytes.len) {
                 var addr_buf: [stack_n]usize = undefined;
                 const free_stack_trace = std.debug.captureCurrentStackTrace(.{ .first_address = ret_addr }, &addr_buf);
+                const tty_config = std.Io.tty.detectConfig(.stderr());
                 log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {f} Free: {f}", .{
                     entry.value_ptr.bytes.len,
                     old_mem.len,
-                    entry.value_ptr.getStackTrace(.alloc),
-                    free_stack_trace,
+                    std.debug.FormatStackTrace{
+                        .stack_trace = entry.value_ptr.getStackTrace(.alloc),
+                        .tty_config = tty_config,
+                    },
+                    std.debug.FormatStackTrace{
+                        .stack_trace = free_stack_trace,
+                        .tty_config = tty_config,
+                    },
                 });
             }
 
@@ -667,11 +703,18 @@ pub fn DebugAllocator(comptime config: Config) type {
             if (config.safety and old_mem.len != entry.value_ptr.bytes.len) {
                 var addr_buf: [stack_n]usize = undefined;
                 const free_stack_trace = std.debug.captureCurrentStackTrace(.{ .first_address = ret_addr }, &addr_buf);
+                const tty_config = std.Io.tty.detectConfig(.stderr());
                 log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {f} Free: {f}", .{
                     entry.value_ptr.bytes.len,
                     old_mem.len,
-                    entry.value_ptr.getStackTrace(.alloc),
-                    free_stack_trace,
+                    std.debug.FormatStackTrace{
+                        .stack_trace = entry.value_ptr.getStackTrace(.alloc),
+                        .tty_config = tty_config,
+                    },
+                    std.debug.FormatStackTrace{
+                        .stack_trace = free_stack_trace,
+                        .tty_config = tty_config,
+                    },
                 });
             }
 
@@ -892,19 +935,33 @@ pub fn DebugAllocator(comptime config: Config) type {
                     var addr_buf: [stack_n]usize = undefined;
                     const free_stack_trace = std.debug.captureCurrentStackTrace(.{ .first_address = return_address }, &addr_buf);
                     if (old_memory.len != requested_size) {
+                        const tty_config = std.Io.tty.detectConfig(.stderr());
                         log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {f} Free: {f}", .{
                             requested_size,
                             old_memory.len,
-                            bucketStackTrace(bucket, slot_count, slot_index, .alloc),
-                            free_stack_trace,
+                            std.debug.FormatStackTrace{
+                                .stack_trace = bucketStackTrace(bucket, slot_count, slot_index, .alloc),
+                                .tty_config = tty_config,
+                            },
+                            std.debug.FormatStackTrace{
+                                .stack_trace = free_stack_trace,
+                                .tty_config = tty_config,
+                            },
                         });
                     }
                     if (alignment != slot_alignment) {
+                        const tty_config = std.Io.tty.detectConfig(.stderr());
                         log.err("Allocation alignment {d} does not match free alignment {d}. Allocation: {f} Free: {f}", .{
                             slot_alignment.toByteUnits(),
                             alignment.toByteUnits(),
-                            bucketStackTrace(bucket, slot_count, slot_index, .alloc),
-                            free_stack_trace,
+                            std.debug.FormatStackTrace{
+                                .stack_trace = bucketStackTrace(bucket, slot_count, slot_index, .alloc),
+                                .tty_config = tty_config,
+                            },
+                            std.debug.FormatStackTrace{
+                                .stack_trace = free_stack_trace,
+                                .tty_config = tty_config,
+                            },
                         });
                     }
                 }
@@ -987,19 +1044,33 @@ pub fn DebugAllocator(comptime config: Config) type {
                 var addr_buf: [stack_n]usize = undefined;
                 const free_stack_trace = std.debug.captureCurrentStackTrace(.{ .first_address = return_address }, &addr_buf);
                 if (memory.len != requested_size) {
+                    const tty_config = std.Io.tty.detectConfig(.stderr());
                     log.err("Allocation size {d} bytes does not match free size {d}. Allocation: {f} Free: {f}", .{
                         requested_size,
                         memory.len,
-                        bucketStackTrace(bucket, slot_count, slot_index, .alloc),
-                        free_stack_trace,
+                        std.debug.FormatStackTrace{
+                            .stack_trace = bucketStackTrace(bucket, slot_count, slot_index, .alloc),
+                            .tty_config = tty_config,
+                        },
+                        std.debug.FormatStackTrace{
+                            .stack_trace = free_stack_trace,
+                            .tty_config = tty_config,
+                        },
                     });
                 }
                 if (alignment != slot_alignment) {
+                    const tty_config = std.Io.tty.detectConfig(.stderr());
                     log.err("Allocation alignment {d} does not match free alignment {d}. Allocation: {f} Free: {f}", .{
                         slot_alignment.toByteUnits(),
                         alignment.toByteUnits(),
-                        bucketStackTrace(bucket, slot_count, slot_index, .alloc),
-                        free_stack_trace,
+                        std.debug.FormatStackTrace{
+                            .stack_trace = bucketStackTrace(bucket, slot_count, slot_index, .alloc),
+                            .tty_config = tty_config,
+                        },
+                        std.debug.FormatStackTrace{
+                            .stack_trace = free_stack_trace,
+                            .tty_config = tty_config,
+                        },
                     });
                 }
             }
diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index 1d49a890e4..fd6e2926c9 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -5,12 +5,14 @@
 //!   slices as well as APIs which accept null-terminated WTF16LE byte buffers.
 
 const builtin = @import("builtin");
+const native_arch = builtin.cpu.arch;
+
 const std = @import("../std.zig");
+const Io = std.Io;
 const mem = std.mem;
 const assert = std.debug.assert;
 const math = std.math;
 const maxInt = std.math.maxInt;
-const native_arch = builtin.cpu.arch;
 const UnexpectedError = std.posix.UnexpectedError;
 
 test {
@@ -2219,25 +2221,25 @@ pub fn peb() *PEB {
 /// Universal Time (UTC).
 /// This function returns the number of nanoseconds since the canonical epoch,
 /// which is the POSIX one (Jan 01, 1970 AD).
-pub fn fromSysTime(hns: i64) i128 {
+pub fn fromSysTime(hns: i64) Io.Timestamp {
     const adjusted_epoch: i128 = hns + std.time.epoch.windows * (std.time.ns_per_s / 100);
-    return adjusted_epoch * 100;
+    return .fromNanoseconds(@intCast(adjusted_epoch * 100));
 }
 
-pub fn toSysTime(ns: i128) i64 {
-    const hns = @divFloor(ns, 100);
+pub fn toSysTime(ns: Io.Timestamp) i64 {
+    const hns = @divFloor(ns.nanoseconds, 100);
     return @as(i64, @intCast(hns)) - std.time.epoch.windows * (std.time.ns_per_s / 100);
 }
 
-pub fn fileTimeToNanoSeconds(ft: FILETIME) i128 {
+pub fn fileTimeToNanoSeconds(ft: FILETIME) Io.Timestamp {
     const hns = (@as(i64, ft.dwHighDateTime) << 32) | ft.dwLowDateTime;
     return fromSysTime(hns);
 }
 
 /// Converts a number of nanoseconds since the POSIX epoch to a Windows FILETIME.
-pub fn nanoSecondsToFileTime(ns: i128) FILETIME {
+pub fn nanoSecondsToFileTime(ns: Io.Timestamp) FILETIME {
     const adjusted: u64 = @bitCast(toSysTime(ns));
-    return FILETIME{
+    return .{
         .dwHighDateTime = @as(u32, @truncate(adjusted >> 32)),
         .dwLowDateTime = @as(u32, @truncate(adjusted)),
     };
@@ -5740,11 +5742,15 @@ pub fn ProcessBaseAddress(handle: HANDLE) ProcessBaseAddressError!HMODULE {
     return ppeb.ImageBaseAddress;
 }
 
-pub fn checkWtf8ToWtf16LeOverflow(wtf8: []const u8, wtf16le: []const u16) error{ BadPathName, NameTooLong }!void {
+pub fn wtf8ToWtf16Le(wtf16le: []u16, wtf8: []const u8) error{ BadPathName, NameTooLong }!usize {
     // Each u8 in UTF-8/WTF-8 correlates to at most one u16 in UTF-16LE/WTF-16LE.
-    if (wtf16le.len >= wtf8.len) return;
-    const utf16_len = std.unicode.calcUtf16LeLenImpl(wtf8, .can_encode_surrogate_half) catch
-        return error.BadPathName;
-    if (utf16_len > wtf16le.len)
-        return error.NameTooLong;
+    if (wtf16le.len < wtf8.len) {
+        const utf16_len = std.unicode.calcUtf16LeLenImpl(wtf8, .can_encode_surrogate_half) catch
+            return error.BadPathName;
+        if (utf16_len > wtf16le.len)
+            return error.NameTooLong;
+    }
+    return std.unicode.wtf8ToWtf16Le(wtf16le, wtf8) catch |err| switch (err) {
+        error.InvalidWtf8 => return error.BadPathName,
+    };
 }
diff --git a/lib/std/posix.zig b/lib/std/posix.zig
index a58204e1dc..02dc6c6087 100644
--- a/lib/std/posix.zig
+++ b/lib/std/posix.zig
@@ -821,6 +821,9 @@ 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,
@@ -2918,8 +2921,7 @@ pub fn chdir(dir_path: []const u8) ChangeCurDirError!void {
         @compileError("WASI does not support os.chdir");
     } else if (native_os == .windows) {
         var wtf16_dir_path: [windows.PATH_MAX_WIDE]u16 = undefined;
-        try windows.checkWtf8ToWtf16LeOverflow(dir_path, &wtf16_dir_path);
-        const len = try std.unicode.wtf8ToWtf16Le(&wtf16_dir_path, dir_path);
+        const len = try windows.wtf8ToWtf16Le(&wtf16_dir_path, dir_path);
         return chdirW(wtf16_dir_path[0..len]);
     } else {
         const dir_path_c = try toPosixPath(dir_path);
@@ -2935,8 +2937,7 @@ pub fn chdirZ(dir_path: [*:0]const u8) ChangeCurDirError!void {
     if (native_os == .windows) {
         const dir_path_span = mem.span(dir_path);
         var wtf16_dir_path: [windows.PATH_MAX_WIDE]u16 = undefined;
-        try windows.checkWtf8ToWtf16LeOverflow(dir_path_span, &wtf16_dir_path);
-        const len = try std.unicode.wtf8ToWtf16Le(&wtf16_dir_path, dir_path_span);
+        const len = try windows.wtf8ToWtf16Le(&wtf16_dir_path, dir_path_span);
         return chdirW(wtf16_dir_path[0..len]);
     } else if (native_os == .wasi and !builtin.link_libc) {
         return chdir(mem.span(dir_path));
diff --git a/lib/std/posix/test.zig b/lib/std/posix/test.zig
index e85f1d7471..3f4b11c1af 100644
--- a/lib/std/posix/test.zig
+++ b/lib/std/posix/test.zig
@@ -862,20 +862,6 @@ test "isatty" {
     try expectEqual(posix.isatty(file.handle), false);
 }
 
-test "read with empty buffer" {
-    var tmp = tmpDir(.{});
-    defer tmp.cleanup();
-
-    var file = try tmp.dir.createFile("read_empty", .{ .read = true });
-    defer file.close();
-
-    const bytes = try a.alloc(u8, 0);
-    defer a.free(bytes);
-
-    const rc = try posix.read(file.handle, bytes);
-    try expectEqual(rc, 0);
-}
-
 test "pread with empty buffer" {
     var tmp = tmpDir(.{});
     defer tmp.cleanup();
diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 02ad99932e..7cef6f9c58 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -1148,6 +1148,7 @@ pub fn checkAllAllocationFailures(backing_allocator: std.mem.Allocator, comptime
         } else |err| switch (err) {
             error.OutOfMemory => {
                 if (failing_allocator_inst.allocated_bytes != failing_allocator_inst.freed_bytes) {
+                    const tty_config = std.Io.tty.detectConfig(.stderr());
                     print(
                         "\nfail_index: {d}/{d}\nallocated bytes: {d}\nfreed bytes: {d}\nallocations: {d}\ndeallocations: {d}\nallocation that was made to fail: {f}",
                         .{
@@ -1157,7 +1158,10 @@ pub fn checkAllAllocationFailures(backing_allocator: std.mem.Allocator, comptime
                             failing_allocator_inst.freed_bytes,
                             failing_allocator_inst.allocations,
                             failing_allocator_inst.deallocations,
-                            failing_allocator_inst.getStackTrace(),
+                            std.debug.FormatStackTrace{
+                                .stack_trace = failing_allocator_inst.getStackTrace(),
+                                .tty_config = tty_config,
+                            },
                         },
                     );
                     return error.MemoryLeakDetected;
diff --git a/tools/incr-check.zig b/tools/incr-check.zig
index 183d59bf88..4c5a2d9978 100644
--- a/tools/incr-check.zig
+++ b/tools/incr-check.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const Io = std.Io;
 const Allocator = std.mem.Allocator;
 const Cache = std.Build.Cache;
 
@@ -11,6 +12,12 @@ pub fn main() !void {
     defer arena_instance.deinit();
     const arena = arena_instance.allocator();
 
+    const gpa = arena;
+
+    var threaded: Io.Threaded = .init(gpa);
+    defer threaded.deinit();
+    const io = threaded.io();
+
     var opt_zig_exe: ?[]const u8 = null;
     var opt_input_file_name: ?[]const u8 = null;
     var opt_lib_dir: ?[]const u8 = null;
@@ -53,7 +60,7 @@ pub fn main() !void {
     const input_file_name = opt_input_file_name orelse fatal("missing input file\n{s}", .{usage});
 
     const input_file_bytes = try std.fs.cwd().readFileAlloc(input_file_name, arena, .limited(std.math.maxInt(u32)));
-    const case = try Case.parse(arena, input_file_bytes);
+    const case = try Case.parse(arena, io, input_file_bytes);
 
     // Check now: if there are any targets using the `cbe` backend, we need the lib dir.
     if (opt_lib_dir == null) {
@@ -86,7 +93,7 @@ pub fn main() !void {
     else
         null;
 
-    const host = try std.zig.system.resolveTargetQuery(.{});
+    const host = try std.zig.system.resolveTargetQuery(io, .{});
 
     const debug_log_verbose = debug_zcu or debug_dwarf or debug_link;
 
@@ -186,7 +193,7 @@ pub fn main() !void {
 
         try child.spawn();
 
-        var poller = std.Io.poll(arena, Eval.StreamEnum, .{
+        var poller = Io.poll(arena, Eval.StreamEnum, .{
             .stdout = child.stdout.?,
             .stderr = child.stderr.?,
         });
@@ -226,7 +233,7 @@ const Eval = struct {
     cc_child_args: *std.ArrayListUnmanaged([]const u8),
 
     const StreamEnum = enum { stdout, stderr };
-    const Poller = std.Io.Poller(StreamEnum);
+    const Poller = Io.Poller(StreamEnum);
 
     /// Currently this function assumes the previous updates have already been written.
     fn write(eval: *Eval, update: Case.Update) void {
@@ -647,7 +654,7 @@ const Case = struct {
         msg: []const u8,
     };
 
-    fn parse(arena: Allocator, bytes: []const u8) !Case {
+    fn parse(arena: Allocator, io: Io, bytes: []const u8) !Case {
         const fatal = std.process.fatal;
 
         var targets: std.ArrayListUnmanaged(Target) = .empty;
@@ -683,7 +690,7 @@ const Case = struct {
                         },
                     }) catch fatal("line {d}: invalid target query '{s}'", .{ line_n, query });
 
-                    const resolved = try std.zig.system.resolveTargetQuery(parsed_query);
+                    const resolved = try std.zig.system.resolveTargetQuery(io, parsed_query);
 
                     try targets.append(arena, .{
                         .query = query,