diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index aed79c9..6cd5777 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,8 +9,18 @@ on:
 jobs:
   build:
     strategy:
+      fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
+        # macos + 0.15.2 is omitted: zig 0.15.2 cannot link against the
+        # macOS 26 SDK on current runner images (and current Macs).
+        # 0.16 support comes via src/compat.zig.
+        include:
+          - os: ubuntu-latest
+            zig: "0.15.2"
+          - os: ubuntu-latest
+            zig: "0.16.0"
+          - os: macos-latest
+            zig: "0.16.0"
 
     runs-on: ${{ matrix.os }}
 
@@ -19,7 +29,7 @@ jobs:
 
       - uses: mlugg/setup-zig@v2
         with:
-          version: 0.15.2
+          version: ${{ matrix.zig }}
 
       - name: Install libgit2 (Linux)
         if: runner.os == 'Linux'
@@ -41,3 +51,6 @@ jobs:
           ./zig-out/bin/nit status
           ./zig-out/bin/nit log -n 5
           ./zig-out/bin/nit show
+
+      - name: Conformance tests
+        run: ./tests/conformance.sh ./zig-out/bin/nit
diff --git a/README.md b/README.md
index 9e4d447..a3c1eb2 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@ We ran [experiments](experiments/) to validate our choice of 1 context line (vs
 
 ## Install
 
-Requires [libgit2](https://libgit2.org/) and [zig](https://ziglang.org/) 0.14+.
+Requires [libgit2](https://libgit2.org/) and [zig](https://ziglang.org/) 0.15.2 or 0.16.0. On recent macOS (26+ SDK) use 0.16.0 - zig 0.15.2 cannot link against that SDK.
 
 ```sh
 # From source
diff --git a/build.zig.zon b/build.zig.zon
index d665392..4fedb1d 100644
--- a/build.zig.zon
+++ b/build.zig.zon
@@ -2,7 +2,7 @@
     .name = .nit,
     .version = "0.1.0",
     .fingerprint = 0x5e5f5af3d86f98f2,
-    .minimum_zig_version = "0.14.0",
+    .minimum_zig_version = "0.15.2",
 
     .paths = .{
         "build.zig",
diff --git a/src/cli.zig b/src/cli.zig
index f7ca5da..ddc99a8 100644
--- a/src/cli.zig
+++ b/src/cli.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const compat = @import("compat.zig");
 const git = @import("git.zig");
 const status = @import("cmd/status.zig");
 const log = @import("cmd/log.zig");
@@ -26,15 +27,14 @@ const usage =
     \\
 ;
 
-pub fn run() !void {
+pub fn run(init: compat.ProcessInit) !void {
     color.init();
 
     var buf: [8192]u8 = undefined;
-    var file_writer = std.fs.File.stdout().writer(&buf);
+    var file_writer = compat.stdoutWriter(init, &buf);
     const w = &file_writer.interface;
 
-    const args = try std.process.argsAlloc(std.heap.page_allocator);
-    defer std.process.argsFree(std.heap.page_allocator, args);
+    const args = try compat.argsSlice(init);
 
     if (args.len < 2) {
         try w.writeAll(usage);
@@ -163,7 +163,5 @@ fn passthrough(args: []const [:0]const u8) !void {
     argv[args.len] = null;
 
     const argv_ptr: [*:null]const ?[*:0]const u8 = @ptrCast(argv.ptr);
-    const envp: [*:null]const ?[*:0]const u8 = @ptrCast(std.c.environ);
-
-    return std.posix.execvpeZ("git", argv_ptr, envp);
+    return compat.execGit(argv_ptr);
 }
diff --git a/src/color.zig b/src/color.zig
index f8b4189..c89ef50 100644
--- a/src/color.zig
+++ b/src/color.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const compat = @import("compat.zig");
 
 // Default ANSI colors (respects terminal theme)
 const defaults = struct {
@@ -54,7 +55,7 @@ fn makeEscape(sgr: []const u8) []const u8 {
 }
 
 pub fn init() void {
-    const env = std.posix.getenv("NIT_COLORS") orelse return;
+    const env = compat.getenv("NIT_COLORS") orelse return;
 
     // Parse "key=value:key=value:..."
     var iter = std.mem.splitScalar(u8, env, ':');
@@ -88,5 +89,5 @@ pub fn init() void {
 }
 
 pub fn isTty() bool {
-    return std.posix.isatty(std.fs.File.stdout().handle);
+    return compat.stdoutIsTty();
 }
diff --git a/src/compat.zig b/src/compat.zig
new file mode 100644
index 0000000..8e461d2
--- /dev/null
+++ b/src/compat.zig
@@ -0,0 +1,57 @@
+//! Zig version compatibility layer.
+//!
+//! nit supports both Zig 0.15.x and 0.16.x (where the std I/O and process
+//! APIs changed shape). Everything version-sensitive lives here so the rest
+//! of the codebase can stay on the shared std.Io.Writer interface, which is
+//! identical across both versions.
+const std = @import("std");
+
+/// Zig 0.16 introduced std.process.Init and moved File I/O behind std.Io.
+pub const is_modern = @hasDecl(std.process, "Init");
+
+/// On 0.16 main receives std.process.Init (which carries the Io instance
+/// and args); on 0.15 main takes no arguments and we reach for globals.
+pub const ProcessInit = if (is_modern) std.process.Init else void;
+
+pub const StdoutWriter = if (is_modern) std.Io.File.Writer else std.fs.File.Writer;
+
+pub fn stdoutWriter(init: ProcessInit, buffer: []u8) StdoutWriter {
+    if (is_modern) {
+        // Streaming, not positional: positional mode pwrites from offset 0,
+        // which overwrites earlier output when stdout is redirected to a file.
+        return std.Io.File.stdout().writerStreaming(init.io, buffer);
+    } else {
+        return std.fs.File.stdout().writer(buffer);
+    }
+}
+
+/// Argument slices live for the whole process (nit is a short-lived CLI):
+/// arena-backed on 0.16, page-allocated and never freed on 0.15.
+pub fn argsSlice(init: ProcessInit) ![]const [:0]const u8 {
+    if (is_modern) {
+        return init.minimal.args.toSlice(init.arena.allocator());
+    } else {
+        const raw = try std.process.argsAlloc(std.heap.page_allocator);
+        return @ptrCast(raw);
+    }
+}
+
+/// libc getenv: identical on both versions (std.posix.getenv was removed in 0.16).
+pub fn getenv(name: [*:0]const u8) ?[]const u8 {
+    const val = std.c.getenv(name) orelse return null;
+    return std.mem.span(val);
+}
+
+pub fn stdoutIsTty() bool {
+    return std.c.isatty(std.posix.STDOUT_FILENO) == 1;
+}
+
+// std.posix.execvpeZ was removed in 0.16; libc execvp (which inherits the
+// process environment) covers both versions since we always link libc.
+extern "c" fn execvp(file: [*:0]const u8, argv: [*:null]const ?[*:0]const u8) c_int;
+
+/// Replace the current process with `git`. Only returns on failure.
+pub fn execGit(argv: [*:null]const ?[*:0]const u8) error{ExecFailed} {
+    _ = execvp("git", argv);
+    return error.ExecFailed;
+}
diff --git a/src/git.zig b/src/git.zig
index 9649a0a..a428c66 100644
--- a/src/git.zig
+++ b/src/git.zig
@@ -9,13 +9,9 @@ pub const Repository = struct {
 
     pub fn openFromCwd() !Repository {
         var repo: ?*c.git_repository = null;
-        const cwd_dir = std.fs.cwd();
-        var buf: [std.fs.max_path_bytes]u8 = undefined;
-        const path = try cwd_dir.realpath(".", &buf);
-        const path_z = try std.heap.page_allocator.dupeZ(u8, path);
-        defer std.heap.page_allocator.free(path_z);
-
-        try check(c.git_repository_open_ext(&repo, path_z, 0, null));
+        // libgit2 resolves the relative path and discovers upward itself;
+        // no need to realpath the cwd first.
+        try check(c.git_repository_open_ext(&repo, ".", 0, null));
         return .{ .repo = repo.? };
     }
 
diff --git a/src/main.zig b/src/main.zig
index fabde75..bab1a72 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,5 +1,14 @@
 const cli = @import("cli.zig");
+const compat = @import("compat.zig");
 
-pub fn main() !void {
-    try cli.run();
+// Zig 0.16 passes std.process.Init to main; 0.15 requires a zero-arg main.
+// compat.ProcessInit keeps both signatures valid on both versions.
+pub const main = if (compat.is_modern) mainModern else mainLegacy;
+
+fn mainModern(init: compat.ProcessInit) !void {
+    try cli.run(init);
+}
+
+fn mainLegacy() !void {
+    try cli.run({});
 }
diff --git a/tests/conformance.sh b/tests/conformance.sh
index b636617..74894ab 100755
--- a/tests/conformance.sh
+++ b/tests/conformance.sh
@@ -22,11 +22,22 @@ fi
 # Resolve to absolute path
 NIT="$(cd "$(dirname "$NIT")" && pwd)/$(basename "$NIT")"
 
+# Run a command under a pseudo-TTY. BSD/macOS script takes the command as
+# positional args; util-linux script needs -c (and %q-quoting, since color
+# values contain semicolons).
+if script -qec true /dev/null >/dev/null 2>&1; then
+  run_tty() { script -qec "$(printf '%q ' "$@")" /dev/null; }
+else
+  run_tty() { script -q /dev/null "$@"; }
+fi
+
 TMPDIR=$(mktemp -d -t nit-conformance-XXXXXX)
 trap "rm -rf $TMPDIR" EXIT
 
 cd "$TMPDIR"
-git init -q
+# -b main: the merge-commit tests checkout main by name, so don't depend
+# on the host's init.defaultBranch
+git init -q -b main
 git config user.email "test@test.com"
 git config user.name "Test User"
 
@@ -731,13 +742,13 @@ check "show HEAD:binary.dat matches git" \
 echo ""
 echo "NIT_COLORS:"
 
-# On macOS, script -q /dev/null forces a pseudo-TTY
+# On macOS, run_tty forces a pseudo-TTY
 # Verify that NIT_COLORS changes output when running in a TTY
 if command -v script >/dev/null 2>&1; then
   # Without NIT_COLORS: default colors in TTY
-  default_out=$(script -q /dev/null $NIT show -H 2>&1 | cat -v | head -3)
+  default_out=$(run_tty $NIT show -H 2>&1 | cat -v | head -3)
   # With NIT_COLORS: custom hash color (magenta = 35)
-  custom_out=$(script -q /dev/null env NIT_COLORS="hash=35" $NIT show -H 2>&1 | cat -v | head -3)
+  custom_out=$(run_tty env NIT_COLORS="hash=35" $NIT show -H 2>&1 | cat -v | head -3)
 
   if [ "$default_out" != "$custom_out" ]; then
     PASS=$((PASS + 1))
@@ -775,7 +786,7 @@ if command -v script >/dev/null 2>&1; then
     "NIT_COLORS='hash=38;2;255;165;0' $NIT log -n 1 2>&1"
 
   # Verify true-color actually produces escape sequence in TTY
-  truecolor_out=$(script -q /dev/null env NIT_COLORS="hash=38;2;255;0;0" $NIT show -H 2>&1 | cat -v | head -1)
+  truecolor_out=$(run_tty env NIT_COLORS="hash=38;2;255;0;0" $NIT show -H 2>&1 | cat -v | head -1)
   if echo "$truecolor_out" | grep -q '38;2;255;0;0'; then
     PASS=$((PASS + 1))
     echo "  PASS: NIT_COLORS true-color escape in TTY output"
@@ -797,8 +808,8 @@ if command -v script >/dev/null 2>&1; then
     "NIT_COLORS='boguskey=32' $NIT log -n 1 2>&1"
 
   # Duplicate keys (last wins) - verify output changes with second value
-  dup_out1=$(script -q /dev/null env NIT_COLORS="hash=35" $NIT show -H 2>&1 | cat -v | head -1)
-  dup_out2=$(script -q /dev/null env NIT_COLORS="hash=33:hash=35" $NIT show -H 2>&1 | cat -v | head -1)
+  dup_out1=$(run_tty env NIT_COLORS="hash=35" $NIT show -H 2>&1 | cat -v | head -1)
+  dup_out2=$(run_tty env NIT_COLORS="hash=33:hash=35" $NIT show -H 2>&1 | cat -v | head -1)
   if [ "$dup_out1" = "$dup_out2" ]; then
     PASS=$((PASS + 1))
     echo "  PASS: NIT_COLORS duplicate keys (last wins)"
@@ -836,7 +847,7 @@ if command -v script >/dev/null 2>&1; then
     "NIT_COLORS='add=31:del=32:hunk=33:context=34:staged=35:unstaged=36:hash=37:date=38:add=39:del=40:hunk=41:context=42' $NIT log -n 1 2>&1"
 
   # NIT_COLORS affects show -H (color slot: hash, date used in show)
-  custom_show=$(script -q /dev/null env NIT_COLORS="hash=35" $NIT show -H 2>&1 | cat -v | head -1)
+  custom_show=$(run_tty env NIT_COLORS="hash=35" $NIT show -H 2>&1 | cat -v | head -1)
   if [ "$default_out" != "$custom_show" ] || echo "$custom_show" | grep -q '35m'; then
     PASS=$((PASS + 1))
     echo "  PASS: NIT_COLORS affects show -H"
@@ -847,8 +858,8 @@ if command -v script >/dev/null 2>&1; then
   fi
 
   # NIT_COLORS affects diff -H (color slot: add, del, hunk, context)
-  default_diff=$(script -q /dev/null $NIT diff -H 2>&1 | cat -v | head -3)
-  custom_diff=$(script -q /dev/null env NIT_COLORS="add=35:del=36" $NIT diff -H 2>&1 | cat -v | head -3)
+  default_diff=$(run_tty $NIT diff -H 2>&1 | cat -v | head -3)
+  custom_diff=$(run_tty env NIT_COLORS="add=35:del=36" $NIT diff -H 2>&1 | cat -v | head -3)
   if [ "$default_diff" != "$custom_diff" ]; then
     PASS=$((PASS + 1))
     echo "  PASS: NIT_COLORS affects diff -H"
@@ -859,8 +870,8 @@ if command -v script >/dev/null 2>&1; then
   fi
 
   # NIT_COLORS affects log -H (color slot: hash, date)
-  default_log=$(script -q /dev/null $NIT log -H -n 1 2>&1 | cat -v | head -1)
-  custom_log=$(script -q /dev/null env NIT_COLORS="hash=35:date=36" $NIT log -H -n 1 2>&1 | cat -v | head -1)
+  default_log=$(run_tty $NIT log -H -n 1 2>&1 | cat -v | head -1)
+  custom_log=$(run_tty env NIT_COLORS="hash=35:date=36" $NIT log -H -n 1 2>&1 | cat -v | head -1)
   if [ "$default_log" != "$custom_log" ]; then
     PASS=$((PASS + 1))
     echo "  PASS: NIT_COLORS affects log -H"
@@ -871,8 +882,8 @@ if command -v script >/dev/null 2>&1; then
   fi
 
   # NIT_COLORS affects status -H (color slot: staged, unstaged)
-  default_status=$(script -q /dev/null $NIT status -H 2>&1 | cat -v)
-  custom_status=$(script -q /dev/null env NIT_COLORS="staged=35:unstaged=36" $NIT status -H 2>&1 | cat -v)
+  default_status=$(run_tty $NIT status -H 2>&1 | cat -v)
+  custom_status=$(run_tty env NIT_COLORS="staged=35:unstaged=36" $NIT status -H 2>&1 | cat -v)
   if [ "$default_status" != "$custom_status" ]; then
     PASS=$((PASS + 1))
     echo "  PASS: NIT_COLORS affects status -H"