diff --git a/src/cli/main.zig b/src/cli/main.zig
index bcf880c616..78ded388a5 100644
--- a/src/cli/main.zig
+++ b/src/cli/main.zig
@@ -1935,7 +1935,7 @@ pub fn rocBundle(gpa: Allocator, args: cli_args.BundleArgs) !void {
         &iter,
         @intCast(args.compression_level),
         &allocator_copy,
-        temp_file.writer(),
+        temp_file.deprecatedWriter(),
         cwd,
         null, // path_prefix parameter - null means no stripping
         &error_ctx,
@@ -2027,7 +2027,7 @@ fn rocUnbundle(allocator: Allocator, args: cli_args.UnbundleArgs) !void {
         var error_ctx: unbundle.ErrorContext = undefined;
         unbundle.unbundleFiles(
             allocator,
-            archive_file.reader(),
+            archive_file.deprecatedReader(),
             output_dir,
             basename,
             &error_ctx,
@@ -2105,7 +2105,7 @@ fn rocBuild(gpa: Allocator, args: cli_args.BuildArgs) !void {
             std.log.info("Cross-compilation from {s} to {s} is supported", .{ @tagName(host_target), @tagName(target) });
         },
         .unsupported_host_target, .unsupported_cross_compilation, .missing_toolchain => {
-            const stderr = std.io.getStdErr().writer();
+            const stderr = std.fs.File.stderr().deprecatedWriter();
             try cross_compilation.printCrossCompilationError(stderr, cross_validation);
             std.process.exit(1);
         },
diff --git a/src/eval/test_runner.zig b/src/eval/test_runner.zig
index 39cb26ef75..082922d7da 100644
--- a/src/eval/test_runner.zig
+++ b/src/eval/test_runner.zig
@@ -26,7 +26,7 @@ const LayoutStore = layout.Store;
 const TypeStore = types.store.Store;
 const CIR = can.CIR;
 
-fn testRocAlloc(alloc_args: *RocAlloc, env: *anyopaque) callconv(.C) void {
+fn testRocAlloc(alloc_args: *RocAlloc, env: *anyopaque) callconv(.c) void {
     const test_env: *TestRunner = @ptrCast(@alignCast(env));
     const align_enum = std.mem.Alignment.fromByteUnits(@as(usize, @intCast(alloc_args.alignment)));
     const size_storage_bytes = @max(alloc_args.alignment, @alignOf(usize));
@@ -40,7 +40,7 @@ fn testRocAlloc(alloc_args: *RocAlloc, env: *anyopaque) callconv(.C) void {
     alloc_args.answer = @ptrFromInt(@intFromPtr(base_ptr) + size_storage_bytes);
 }
 
-fn testRocDealloc(dealloc_args: *RocDealloc, env: *anyopaque) callconv(.C) void {
+fn testRocDealloc(dealloc_args: *RocDealloc, env: *anyopaque) callconv(.c) void {
     const test_env: *TestRunner = @ptrCast(@alignCast(env));
     const size_storage_bytes = @max(dealloc_args.alignment, @alignOf(usize));
     const size_ptr: *const usize = @ptrFromInt(@intFromPtr(dealloc_args.ptr) - @sizeOf(usize));
@@ -52,7 +52,7 @@ fn testRocDealloc(dealloc_args: *RocDealloc, env: *anyopaque) callconv(.C) void
     test_env.allocator.rawFree(slice, align_enum, @returnAddress());
 }
 
-fn testRocRealloc(realloc_args: *RocRealloc, env: *anyopaque) callconv(.C) void {
+fn testRocRealloc(realloc_args: *RocRealloc, env: *anyopaque) callconv(.c) void {
     const test_env: *TestRunner = @ptrCast(@alignCast(env));
     const size_storage_bytes = @max(realloc_args.alignment, @alignOf(usize));
     const old_size_ptr: *const usize = @ptrFromInt(@intFromPtr(realloc_args.answer) - @sizeOf(usize));
@@ -68,19 +68,19 @@ fn testRocRealloc(realloc_args: *RocRealloc, env: *anyopaque) callconv(.C) void
     realloc_args.answer = @ptrFromInt(@intFromPtr(new_slice.ptr) + size_storage_bytes);
 }
 
-fn testRocDbg(dbg_args: *const RocDbg, env: *anyopaque) callconv(.C) void {
+fn testRocDbg(dbg_args: *const RocDbg, env: *anyopaque) callconv(.c) void {
     _ = dbg_args;
     _ = env;
     @panic("testRocDbg not implemented yet");
 }
 
-fn testRocExpectFailed(expect_args: *const RocExpectFailed, env: *anyopaque) callconv(.C) void {
+fn testRocExpectFailed(expect_args: *const RocExpectFailed, env: *anyopaque) callconv(.c) void {
     _ = expect_args;
     _ = env;
     @panic("testRocExpectFailed not implemented yet");
 }
 
-fn testRocCrashed(crashed_args: *const RocCrashed, env: *anyopaque) callconv(.C) void {
+fn testRocCrashed(crashed_args: *const RocCrashed, env: *anyopaque) callconv(.c) void {
     const test_env: *TestRunner = @ptrCast(@alignCast(env));
     const msg_slice = crashed_args.utf8_bytes[0..crashed_args.len];
 
@@ -116,7 +116,7 @@ pub const TestRunner = struct {
     env: *const ModuleEnv,
     interpreter: Interpreter,
     roc_ops: ?RocOps,
-    test_results: std.ArrayList(TestResult),
+    test_results: std.array_list.Managed(TestResult),
 
     pub fn init(
         allocator: std.mem.Allocator,
@@ -130,7 +130,7 @@ pub const TestRunner = struct {
             .env = cir,
             .interpreter = try Interpreter.init(allocator, cir, stack_memory, layout_cache, type_store),
             .roc_ops = null,
-            .test_results = std.ArrayList(TestResult).init(allocator),
+            .test_results = std.array_list.Managed(TestResult).init(allocator),
         };
 
         return runner;
diff --git a/src/fs/Filesystem.zig b/src/fs/Filesystem.zig
index c4c8d1f5f4..a7808a237f 100644
--- a/src/fs/Filesystem.zig
+++ b/src/fs/Filesystem.zig
@@ -202,7 +202,7 @@ fn readFileDefault(relative_path: []const u8, allocator: std.mem.Allocator) Read
     const file = try std.fs.cwd().openFile(relative_path, .{});
     defer file.close();
 
-    const contents = try file.reader().readAllAlloc(allocator, max_file_size);
+    const contents = try file.deprecatedReader().readAllAlloc(allocator, max_file_size);
 
     return contents;
 }
@@ -213,7 +213,7 @@ fn readFileIntoDefault(path: []const u8, buffer: []u8) ReadError!usize {
     const file = try std.fs.cwd().openFile(path, .{});
     defer file.close();
 
-    return try file.reader().readAll(buffer);
+    return try file.deprecatedReader().readAll(buffer);
 }
 
 fn openDirDefault(absolute_path: []const u8) OpenError!Dir {