diff --git a/skainet-io/skainet-io-core/src/mingwX64Main/kotlin/sk/ainet/io/WindowsRandomAccessSource.kt b/skainet-io/skainet-io-core/src/mingwX64Main/kotlin/sk/ainet/io/WindowsRandomAccessSource.kt
new file mode 100644
index 000000000..1c801d707
--- /dev/null
+++ b/skainet-io/skainet-io-core/src/mingwX64Main/kotlin/sk/ainet/io/WindowsRandomAccessSource.kt
@@ -0,0 +1,134 @@
+package sk.ainet.io
+
+import kotlinx.cinterop.ExperimentalForeignApi
+import kotlinx.cinterop.addressOf
+import kotlinx.cinterop.alloc
+import kotlinx.cinterop.convert
+import kotlinx.cinterop.memScoped
+import kotlinx.cinterop.ptr
+import kotlinx.cinterop.usePinned
+import kotlinx.cinterop.value
+import platform.windows.CloseHandle
+import platform.windows.CreateFileW
+import platform.windows.DWORDVar
+import platform.windows.ERROR_HANDLE_EOF
+import platform.windows.FILE_ATTRIBUTE_NORMAL
+import platform.windows.FILE_SHARE_READ
+import platform.windows.GENERIC_READ
+import platform.windows.GetFileSizeEx
+import platform.windows.GetLastError
+import platform.windows.HANDLE
+import platform.windows.INVALID_HANDLE_VALUE
+import platform.windows.LARGE_INTEGER
+import platform.windows.OPEN_EXISTING
+import platform.windows.OVERLAPPED
+import platform.windows.ReadFile
+
+/**
+ * Windows [RandomAccessSource] backed by `ReadFile` with an `OVERLAPPED` offset.
+ *
+ * POSIX `pread(2)` does not exist on mingw; passing an `OVERLAPPED` structure with an
+ * explicit 64-bit offset to `ReadFile` gives the same positional semantics — every call
+ * names its own offset, so concurrent reads from different positions are safe without
+ * locking, and files > 2 GB work (offset is split into `Offset`/`OffsetHigh`).
+ *
+ * This is deliberately a separate leaf implementation: `mingwX64Main` must stay out of
+ * this module's `native64Main` source set (that set is POSIX-`pread`-shaped and LP64;
+ * mingw is LLP64). [close] is single-shot. See #911.
+ */
+@OptIn(ExperimentalForeignApi::class)
+public class WindowsRandomAccessSource private constructor(
+    private val handle: HANDLE,
+    override val size: Long,
+) : RandomAccessSource {
+
+    private var closed = false
+
+    override fun readAt(position: Long, length: Int): ByteArray {
+        require(position >= 0) { "Position must be non-negative: $position" }
+        require(length >= 0) { "Length must be non-negative: $length" }
+        require(position + length <= size) {
+            "Read beyond end of file: position=$position, length=$length, size=$size"
+        }
+        if (length == 0) return ByteArray(0)
+
+        val buffer = ByteArray(length)
+        val bytesRead = readAt(position, buffer, 0, length)
+        return if (bytesRead < length) buffer.copyOf(bytesRead) else buffer
+    }
+
+    override fun readAt(position: Long, buffer: ByteArray, offset: Int, length: Int): Int {
+        require(position >= 0) { "Position must be non-negative: $position" }
+        require(offset >= 0) { "Offset must be non-negative: $offset" }
+        require(length >= 0) { "Length must be non-negative: $length" }
+        require(offset + length <= buffer.size) {
+            "Buffer overflow: offset=$offset, length=$length, buffer.size=${buffer.size}"
+        }
+        check(!closed) { "Source is closed" }
+        if (length == 0) return 0
+
+        return buffer.usePinned { pinned ->
+            var totalRead = 0
+            while (totalRead < length) {
+                val chunk = memScoped {
+                    val pos = position + totalRead
+                    val overlapped = alloc<OVERLAPPED>()
+                    overlapped.Offset = (pos and 0xFFFF_FFFFL).toUInt()
+                    overlapped.OffsetHigh = (pos ushr 32).toUInt()
+                    val read = alloc<DWORDVar>()
+                    val ok = ReadFile(
+                        handle,
+                        pinned.addressOf(offset + totalRead),
+                        (length - totalRead).convert(),
+                        read.ptr,
+                        overlapped.ptr,
+                    )
+                    if (ok == 0) {
+                        val err = GetLastError()
+                        if (err == ERROR_HANDLE_EOF.toUInt()) return@memScoped 0
+                        error("ReadFile failed at offset $pos: Win32 error $err")
+                    }
+                    read.value.toInt()
+                }
+                if (chunk == 0) break // EOF
+                totalRead += chunk
+            }
+            totalRead
+        }
+    }
+
+    override fun close() {
+        if (closed) return
+        closed = true
+        CloseHandle(handle)
+    }
+
+    public companion object {
+        /**
+         * Open [path] for read-only random access. Returns `null` if the file cannot be
+         * opened or sized — matching the JVM/POSIX implementations, so consumers fall
+         * back to the legacy sequential reader.
+         */
+        public fun open(path: String): WindowsRandomAccessSource? {
+            val handle = CreateFileW(
+                path,
+                GENERIC_READ.convert(),
+                FILE_SHARE_READ.convert(),
+                null,
+                OPEN_EXISTING.convert(),
+                FILE_ATTRIBUTE_NORMAL.convert(),
+                null,
+            )
+            if (handle == null || handle == INVALID_HANDLE_VALUE) return null
+            return memScoped {
+                val sizeVar = alloc<LARGE_INTEGER>()
+                if (GetFileSizeEx(handle, sizeVar.ptr) == 0) {
+                    CloseHandle(handle)
+                    null
+                } else {
+                    WindowsRandomAccessSource(handle, sizeVar.QuadPart)
+                }
+            }
+        }
+    }
+}
diff --git a/skainet-io/skainet-io-core/src/mingwX64Test/kotlin/sk/ainet/io/WindowsRandomAccessSourceTest.kt b/skainet-io/skainet-io-core/src/mingwX64Test/kotlin/sk/ainet/io/WindowsRandomAccessSourceTest.kt
new file mode 100644
index 000000000..c7283a5ee
--- /dev/null
+++ b/skainet-io/skainet-io-core/src/mingwX64Test/kotlin/sk/ainet/io/WindowsRandomAccessSourceTest.kt
@@ -0,0 +1,126 @@
+package sk.ainet.io
+
+import kotlinx.io.buffered
+import kotlinx.io.files.Path
+import kotlinx.io.files.SystemFileSystem
+import kotlinx.io.files.SystemTemporaryDirectory
+import kotlinx.io.write
+import kotlin.test.AfterTest
+import kotlin.test.BeforeTest
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+class WindowsRandomAccessSourceTest {
+
+    private val expected = ByteArray(8192) { (it and 0xFF).toByte() } // 0..255 repeating
+    private lateinit var path: Path
+
+    @BeforeTest
+    fun setUp() {
+        path = Path(SystemTemporaryDirectory, "win-read-test-${kotlin.random.Random.nextLong()}.bin")
+        SystemFileSystem.sink(path).buffered().use { it.write(expected) }
+    }
+
+    @AfterTest
+    fun tearDown() {
+        if (SystemFileSystem.exists(path)) SystemFileSystem.delete(path)
+    }
+
+    @Test
+    fun open_reports_correct_size() {
+        val src = WindowsRandomAccessSource.open(path.toString())!!
+        try {
+            assertEquals(expected.size.toLong(), src.size)
+        } finally {
+            src.close()
+        }
+    }
+
+    @Test
+    fun read_at_zero_returns_prefix() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            val got = src.readAt(0, 16)
+            assertContentEquals(expected.copyOfRange(0, 16), got)
+        }
+    }
+
+    @Test
+    fun read_at_arbitrary_offset_returns_slice() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            val got = src.readAt(1234, 256)
+            assertContentEquals(expected.copyOfRange(1234, 1234 + 256), got)
+        }
+    }
+
+    @Test
+    fun read_at_end_returns_suffix() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            val got = src.readAt(expected.size - 32L, 32)
+            assertContentEquals(expected.copyOfRange(expected.size - 32, expected.size), got)
+        }
+    }
+
+    @Test
+    fun read_into_buffer_reports_bytes_read() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            val buf = ByteArray(64)
+            val n = src.readAt(100L, buf, 0, 64)
+            assertEquals(64, n)
+            assertContentEquals(expected.copyOfRange(100, 164), buf)
+        }
+    }
+
+    @Test
+    fun read_into_buffer_with_offset() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            val buf = ByteArray(128)
+            val n = src.readAt(50L, buf, offset = 32, length = 64)
+            assertEquals(64, n)
+            assertContentEquals(expected.copyOfRange(50, 114), buf.copyOfRange(32, 96))
+            // Bytes outside the requested window must remain zero.
+            for (i in 0 until 32) assertEquals(0, buf[i])
+            for (i in 96 until 128) assertEquals(0, buf[i])
+        }
+    }
+
+    @Test
+    fun read_past_end_throws() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            assertFailsWith<IllegalArgumentException> { src.readAt(expected.size - 1L, 16) }
+        }
+    }
+
+    @Test
+    fun negative_position_throws() {
+        WindowsRandomAccessSource.open(path.toString())!!.use { src ->
+            assertFailsWith<IllegalArgumentException> { src.readAt(-1L, 4) }
+        }
+    }
+
+    @Test
+    fun read_after_close_throws() {
+        val src = WindowsRandomAccessSource.open(path.toString())!!
+        src.close()
+        assertFailsWith<IllegalStateException> {
+            src.readAt(0L, ByteArray(4), 0, 4)
+        }
+    }
+
+    @Test
+    fun close_is_idempotent() {
+        val src = WindowsRandomAccessSource.open(path.toString())!!
+        src.close()
+        src.close() // must not throw
+        assertTrue(true)
+    }
+
+    @Test
+    fun open_missing_file_returns_null() {
+        val missing = Path(SystemTemporaryDirectory, "definitely-does-not-exist-${kotlin.random.Random.nextLong()}.bin")
+        assertNull(WindowsRandomAccessSource.open(missing.toString()))
+    }
+}
diff --git a/skainet-io/skainet-io-gguf/build.gradle.kts b/skainet-io/skainet-io-gguf/build.gradle.kts
index 0d6b25956..308b54ccd 100644
--- a/skainet-io/skainet-io-gguf/build.gradle.kts
+++ b/skainet-io/skainet-io-gguf/build.gradle.kts
@@ -1,74 +1,50 @@
-import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 plugins {
-    alias(libs.plugins.kotlinMultiplatform)
+    id("sk.ainet.multiplatform")
     alias(libs.plugins.androidMultiplatformLibrary)
     alias(libs.plugins.vanniktech.mavenPublish)
     id("sk.ainet.dokka")
 }
 
-kotlin {
-    targets.configureEach {
-        compilations.configureEach {
-            compileTaskProvider.get().compilerOptions {
-                freeCompilerArgs.add("-Xexpect-actual-classes")
-            }
-        }
-    }
-
-    jvm()
-    android {
-        namespace = "sk.ainet.io.gguf"
-        compileSdk = libs.versions.android.compileSdk.get().toInt()
-        minSdk = libs.versions.android.minSdk.get().toInt()
-        compilerOptions {
-            jvmTarget.set(JvmTarget.JVM_1_8)
-        }
-    }
-
-    iosArm64()
-    iosSimulatorArm64()
-    macosArm64 ()
-    linuxX64 ()
-    linuxArm64 ()
-
-    js {
-        browser()
-    }
-
-    @OptIn(ExperimentalWasmDsl::class)
-    wasmJs {
-        browser()
-    }
-
-    @OptIn(ExperimentalWasmDsl::class)
-    wasmWasi {
-        nodejs()
-    }
+// Targets come from skainet.targets in this module's gradle.properties (mingw per #911:
+// its createRandomAccessSource actual routes to io-core's WindowsRandomAccessSource).
+// explicitApi(), kotlin-test and -Xexpect-actual-classes come from sk.ainet.multiplatform.
+skainet {
+    namespace = "sk.ainet.io.gguf"
+    androidJvmTarget = JvmTarget.JVM_1_8
+    expectActualClasses = true
+    // Pre-migration behavior: this module never enabled explicit API mode; turning it on
+    // is a separate cleanup from the #911 target work.
+    explicitApi = false
+}
 
+kotlin {
     sourceSets {
-        val commonMain by getting {
-            dependencies {
-                implementation(libs.kotlinx.io.core)
-                implementation(project(":skainet-lang:skainet-lang-core"))
-                implementation(project(":skainet-io:skainet-io-core"))
-                implementation(project(":skainet-compile:skainet-compile-core"))
-                implementation(project(":skainet-compile:skainet-compile-dag"))
-
-            }
-        }
-        val commonTest by getting {
-            dependencies {
-                implementation(libs.kotlin.test)
-            }
+        // This module opts out of the default hierarchy template
+        // (kotlin.mpp.applyDefaultHierarchyTemplate=false in gradle.properties) — custom
+        // dependsOn edges would silently disable it anyway — and wires the native tree by
+        // hand: the posix `pread`-backed createRandomAccessSource actual is shared by the
+        // Apple and Linux targets via `posixMain`, while mingwX64 hangs off `nativeMain`
+        // directly with its own Win32-backed leaf actual (posix pread does not exist
+        // there). No apple/linux intermediates: no sources live at that level.
+        nativeMain { dependsOn(commonMain.get()) }
+        val posixMain by creating { dependsOn(nativeMain.get()) }
+        listOf(iosArm64Main, iosSimulatorArm64Main, macosArm64Main, linuxX64Main, linuxArm64Main)
+            .forEach { it.get().dependsOn(posixMain) }
+        mingwX64Main { dependsOn(nativeMain.get()) }
+
+        commonMain.dependencies {
+            implementation(libs.kotlinx.io.core)
+            implementation(project(":skainet-lang:skainet-lang-core"))
+            implementation(project(":skainet-io:skainet-io-core"))
+            implementation(project(":skainet-compile:skainet-compile-core"))
+            implementation(project(":skainet-compile:skainet-compile-dag"))
         }
-        val jvmTest by getting {
-            dependencies {
-                implementation(libs.junit)
-                implementation(libs.kotlinx.coroutines)
-                implementation(libs.kotlinx.coroutines.test)
-            }
+        jvmTest.dependencies {
+            implementation(libs.junit)
+            implementation(libs.kotlinx.coroutines)
+            implementation(libs.kotlinx.coroutines.test)
         }
     }
 }
diff --git a/skainet-io/skainet-io-gguf/gradle.properties b/skainet-io/skainet-io-gguf/gradle.properties
index a7d40a9a5..ca2741c59 100644
--- a/skainet-io/skainet-io-gguf/gradle.properties
+++ b/skainet-io/skainet-io-gguf/gradle.properties
@@ -1,2 +1,4 @@
 POM_ARTIFACT_ID=skainet-io-gguf
-POM_NAME=skainet IO API
\ No newline at end of file
+POM_NAME=skainet IO API
+skainet.targets=jvm,js,wasmJs,wasmWasi,apple,linux,mingw
+kotlin.mpp.applyDefaultHierarchyTemplate=false
diff --git a/skainet-io/skainet-io-gguf/src/mingwX64Main/kotlin/sk/ainet/io/gguf/RandomAccessSourceFactory.mingw.kt b/skainet-io/skainet-io-gguf/src/mingwX64Main/kotlin/sk/ainet/io/gguf/RandomAccessSourceFactory.mingw.kt
new file mode 100644
index 000000000..f32ae9339
--- /dev/null
+++ b/skainet-io/skainet-io-gguf/src/mingwX64Main/kotlin/sk/ainet/io/gguf/RandomAccessSourceFactory.mingw.kt
@@ -0,0 +1,13 @@
+package sk.ainet.io.gguf
+
+import sk.ainet.io.RandomAccessSource
+import sk.ainet.io.WindowsRandomAccessSource
+
+/**
+ * Windows implementation of [createRandomAccessSource]: `ReadFile` with an `OVERLAPPED`
+ * offset via io-core's [WindowsRandomAccessSource] (posix `pread` does not exist on
+ * mingw). Returns `null` if the file cannot be opened, matching the JVM/POSIX actuals'
+ * contract so callers can fall back to the legacy sequential reader. See #911.
+ */
+public actual fun createRandomAccessSource(filePath: String): RandomAccessSource? =
+    WindowsRandomAccessSource.open(filePath)
diff --git a/skainet-io/skainet-io-gguf/src/posixMain/kotlin/sk/ainet/io/gguf/RandomAccessSourceFactory.posix.kt b/skainet-io/skainet-io-gguf/src/posixMain/kotlin/sk/ainet/io/gguf/RandomAccessSourceFactory.posix.kt
new file mode 100644
index 000000000..5cd3b2086
--- /dev/null
+++ b/skainet-io/skainet-io-gguf/src/posixMain/kotlin/sk/ainet/io/gguf/RandomAccessSourceFactory.posix.kt
@@ -0,0 +1,14 @@
+package sk.ainet.io.gguf
+
+import sk.ainet.io.PosixPreadRandomAccessSource
+import sk.ainet.io.RandomAccessSource
+
+/**
+ * Native implementation of [createRandomAccessSource] using POSIX `pread(2)`.
+ *
+ * Returns `null` if the file cannot be opened (missing, permission denied,
+ * etc.), matching the JVM actual's contract so callers can fall back to the
+ * legacy sequential reader.
+ */
+public actual fun createRandomAccessSource(filePath: String): RandomAccessSource? =
+    PosixPreadRandomAccessSource.open(filePath)