diff --git a/google-cloud-storage/src/main/java/com/google/cloud/storage/BidiAppendableUnbufferedWritableByteChannel.java b/google-cloud-storage/src/main/java/com/google/cloud/storage/BidiAppendableUnbufferedWritableByteChannel.java
new file mode 100644
index 0000000000..1f9eb7698d
--- /dev/null
+++ b/google-cloud-storage/src/main/java/com/google/cloud/storage/BidiAppendableUnbufferedWritableByteChannel.java
@@ -0,0 +1,193 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.storage;
+
+import com.google.cloud.BaseServiceException;
+import com.google.cloud.storage.ChunkSegmenter.ChunkSegment;
+import com.google.cloud.storage.UnbufferedWritableByteChannelSession.UnbufferedWritableByteChannel;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.ClosedChannelException;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+final class BidiAppendableUnbufferedWritableByteChannel implements UnbufferedWritableByteChannel {
+  private static final Logger LOGGER =
+      LoggerFactory.getLogger(BidiAppendableUnbufferedWritableByteChannel.class);
+
+  private final BidiUploadStreamingStream stream;
+  private final ChunkSegmenter chunkSegmenter;
+
+  private boolean open;
+  private long writeOffset;
+  private volatile boolean nextWriteShouldFinalize;
+  private boolean writeCalledAtLeastOnce;
+
+  /** If write throws an error, don't attempt to finalize things when {@link #close()} is called. */
+  private boolean writeThrewError;
+
+  BidiAppendableUnbufferedWritableByteChannel(
+      BidiUploadStreamingStream stream, ChunkSegmenter chunkSegmenter, long writeOffset) {
+    this.stream = stream;
+    this.chunkSegmenter = chunkSegmenter;
+    this.open = true;
+    this.writeOffset = writeOffset;
+    this.nextWriteShouldFinalize = false;
+    this.writeThrewError = false;
+  }
+
+  @Override
+  public long write(ByteBuffer[] srcs, int srcsOffset, int srcsLength) throws IOException {
+    return internalWrite(srcs, srcsOffset, srcsLength);
+  }
+
+  @Override
+  public long writeAndClose(ByteBuffer[] srcs, int offset, int length) throws IOException {
+    long totalRemaining = Buffers.totalRemaining(srcs, offset, length);
+    long written = 0;
+    do {
+      written += internalWrite(srcs, offset, length);
+    } while (written < totalRemaining);
+    close();
+    return written;
+  }
+
+  @Override
+  public boolean isOpen() {
+    return open;
+  }
+
+  @Override
+  public void close() throws IOException {
+    if (!open) {
+      return;
+    }
+    try {
+      if (writeThrewError) {
+        return;
+      }
+
+      if (!writeCalledAtLeastOnce) {
+        stream.flush();
+      }
+      if (nextWriteShouldFinalize) {
+        //noinspection StatementWithEmptyBody
+        while (!stream.finishWrite(writeOffset)) {}
+      } else {
+        //noinspection StatementWithEmptyBody
+        while (!stream.closeStream(writeOffset)) {}
+      }
+
+      awaitResultFuture();
+    } finally {
+      stream.sendClose();
+      open = false;
+    }
+  }
+
+  public void nextWriteShouldFinalize() {
+    this.nextWriteShouldFinalize = true;
+  }
+
+  private long internalWrite(ByteBuffer[] srcs, int srcsOffset, int srcsLength) throws IOException {
+    if (!open) {
+      throw new ClosedChannelException();
+    }
+    // error early. if the result future is already failed, await it to throw the error
+    if (stream.getResultFuture().isDone()) {
+      awaitResultFuture();
+      return 0;
+    }
+    writeCalledAtLeastOnce = true;
+
+    long availableCapacity = stream.availableCapacity();
+    if (availableCapacity <= 0) {
+      return 0;
+    }
+    RewindableContent rewindableContent = RewindableContent.of(srcs, srcsOffset, srcsLength);
+    long totalBufferRemaining = rewindableContent.getLength();
+
+    ChunkSegment[] data = chunkSegmenter.segmentBuffers(srcs, srcsOffset, srcsLength, true);
+    if (data.length == 0) {
+      return 0;
+    }
+
+    long bytesConsumed = 0;
+    for (int i = 0, len = data.length, lastIdx = len - 1; i < len; i++) {
+      ChunkSegment datum = data[i];
+      int size = datum.getB().size();
+      boolean appended;
+      if (i < lastIdx) {
+        appended = stream.append(datum);
+      } else if (i == lastIdx && nextWriteShouldFinalize) {
+        appended = stream.appendAndFinalize(datum);
+      } else {
+        appended = stream.appendAndFlush(datum);
+      }
+      if (appended) {
+        bytesConsumed += size;
+        writeOffset += size;
+      } else {
+        // if we weren't able to trigger a flush by reaching the end of the array and calling
+        // appendAndFlush, explicitly call flush here so that some progress can be made.
+        // we prefer appendAndFlush so a separate message is not needed, but an extra message
+        // in order to make progress and free buffer space is better than ending up in a live-lock.
+        stream.flush();
+        break;
+      }
+    }
+
+    if (bytesConsumed != totalBufferRemaining) {
+      rewindableContent.rewindTo(bytesConsumed);
+    }
+
+    return bytesConsumed;
+  }
+
+  private void awaitResultFuture() throws IOException {
+    try {
+      stream.getResultFuture().get(10_717, TimeUnit.MILLISECONDS);
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      InterruptedIOException ioe = new InterruptedIOException();
+      ioe.initCause(e);
+      writeThrewError = true;
+      throw ioe;
+    } catch (ExecutionException e) {
+      BaseServiceException coalesce = StorageException.coalesce(e.getCause());
+      String message = coalesce.getMessage();
+      String ioExceptionMessage = message;
+      // if the failure is an upload scenario we detect client side, it's message will be
+      // verbose. To avoid duplication, select the first line only for the io exception
+      int firstNewLineIndex = message != null ? message.indexOf('\n') : -1;
+      if (firstNewLineIndex > -1) {
+        ioExceptionMessage = message.substring(0, firstNewLineIndex);
+      }
+      IOException ioException = new IOException(ioExceptionMessage, coalesce);
+      // ioException.addSuppressed(new AsyncStorageTaskException());
+      writeThrewError = true;
+      throw ioException;
+    } catch (TimeoutException e) {
+      writeThrewError = true;
+      throw new IOException(e);
+    }
+  }
+}