diff --git a/src/commands/connect/client.rs b/src/commands/connect/client.rs
index 5b45c9b..592746d 100644
--- a/src/commands/connect/client.rs
+++ b/src/commands/connect/client.rs
@@ -409,6 +409,7 @@ pub struct BlobParts {
 pub struct CompletedPart {
     pub part_number: u64,
     pub etag: String,
+    pub checksum_sha256: String,
 }
 
 // ---------------------------------------------------------------------------
@@ -1038,8 +1039,9 @@ impl ConnectClient {
         &self,
         presigned_url: &str,
         body: Vec<u8>,
+        checksum_sha256: &str,
     ) -> Result<String, UploadPartError> {
-        self.upload_part_with_progress(presigned_url, body, None)
+        self.upload_part_with_progress(presigned_url, body, checksum_sha256, None)
             .await
     }
 
@@ -1049,6 +1051,7 @@ impl ConnectClient {
         &self,
         presigned_url: &str,
         body: Vec<u8>,
+        checksum_sha256: &str,
         progress: Option<&indicatif::ProgressBar>,
     ) -> Result<String, UploadPartError> {
         let body_len = body.len();
@@ -1078,6 +1081,7 @@ impl ConnectClient {
             self.http
                 .put(presigned_url)
                 .header("content-length", body_len)
+                .header("x-amz-checksum-sha256", checksum_sha256)
                 .body(reqwest::Body::wrap_stream(stream))
                 .send()
                 .await
@@ -1087,6 +1091,7 @@ impl ConnectClient {
         } else {
             self.http
                 .put(presigned_url)
+                .header("x-amz-checksum-sha256", checksum_sha256)
                 .body(body)
                 .send()
                 .await
diff --git a/src/commands/connect/upload.rs b/src/commands/connect/upload.rs
index 0628fc1..315ccca 100644
--- a/src/commands/connect/upload.rs
+++ b/src/commands/connect/upload.rs
@@ -1,4 +1,5 @@
 use anyhow::{Context, Result};
+use base64::prelude::*;
 use indicatif::{MultiProgress, ProgressBar, ProgressStyle};
 use sha2::{Digest, Sha256};
 use std::path::{Path, PathBuf};
@@ -601,6 +602,8 @@ impl ConnectUploadCommand {
                         )
                     })?;
 
+                    let checksum = BASE64_STANDARD.encode(Sha256::digest(&buf));
+
                     let permit = sem
                         .clone()
                         .acquire_owned()
@@ -623,7 +626,7 @@ impl ConnectUploadCommand {
                                 pb.set_position(pb.position().saturating_sub(cs));
                             }
                             match connect
-                                .upload_part_with_progress(&url, buf.clone(), Some(&pb))
+                                .upload_part_with_progress(&url, buf.clone(), &checksum, Some(&pb))
                                 .await
                             {
                                 Ok(e) => {
@@ -650,6 +653,7 @@ impl ConnectUploadCommand {
                         Ok(CompletedPart {
                             part_number: part_num,
                             etag: etag.unwrap(),
+                            checksum_sha256: checksum,
                         })
                     });
                     upload_handles.push(handle);
@@ -954,6 +958,8 @@ async fn upload_artifacts(
             let mut buf = vec![0u8; chunk_size];
             file.read_exact(&mut buf).await?;
 
+            let checksum = BASE64_STANDARD.encode(Sha256::digest(&buf));
+
             // Retry up to 3 times for transient failures.
             // On URL expiry, refresh presigned URLs and retry immediately — no cap on refreshes
             // since fetching a new URL is safe (the S3 multipart upload_id does not expire).
@@ -971,7 +977,10 @@ async fn upload_artifacts(
                         )
                     })?;
 
-                match connect.upload_part(&upload_url, buf.clone()).await {
+                match connect
+                    .upload_part(&upload_url, buf.clone(), &checksum)
+                    .await
+                {
                     Ok(e) => break e,
                     Err(UploadPartError::UrlExpired { .. }) => {
                         eprintln!(
@@ -1016,6 +1025,7 @@ async fn upload_artifacts(
             completed_parts.push(CompletedPart {
                 part_number: part.part_number,
                 etag,
+                checksum_sha256: checksum,
             });
 
             pb.set_position(std::cmp::min(offset + PART_SIZE, artifact.size_bytes));