diff --git a/packages/mcp-core/src/api-client/schema.ts b/packages/mcp-core/src/api-client/schema.ts
index bd1f456e3..85167b782 100644
--- a/packages/mcp-core/src/api-client/schema.ts
+++ b/packages/mcp-core/src/api-client/schema.ts
@@ -1347,7 +1347,8 @@ export const EventAttachmentSchema = z.object({
   size: z.number(),
   mimetype: z.string(),
   dateCreated: z.string().datetime(),
-  sha1: z.string(),
+  // Objectstore-backed attachments do not store a usable SHA1 (checksum is
+  // unavailable), so we neither require nor surface it from this endpoint.
   headers: z.record(z.string(), z.string()).optional(),
 });
 
diff --git a/packages/mcp-core/src/tools/catalog/get-event-attachment.test.ts b/packages/mcp-core/src/tools/catalog/get-event-attachment.test.ts
index b1b9b9ebe..280ad211a 100644
--- a/packages/mcp-core/src/tools/catalog/get-event-attachment.test.ts
+++ b/packages/mcp-core/src/tools/catalog/get-event-attachment.test.ts
@@ -36,7 +36,6 @@ describe("get_event_attachment", () => {
       **Size:** 1024 bytes
       **MIME Type:** image/png
       **Created:** 2025-04-08T21:15:04.000Z
-      **SHA1:** abc123def456
 
       To download this attachment with the attachmentId provided:
       Use the Sentry tool \`get_event_attachment\`
@@ -87,7 +86,6 @@ describe("get_event_attachment", () => {
       **Size:** 1024 bytes
       **MIME Type:** image/png
       **Created:** 2025-04-08T21:15:04.000Z
-      **SHA1:** abc123def456
 
       **Download URL:** https://sentry.io/api/0/projects/sentry-mcp-evals/cloudflare-mcp/events/7ca573c0f4814912aaa9bdc77d1a7d51/attachments/123/?download=1
 
diff --git a/packages/mcp-core/src/tools/catalog/get-event-attachment.ts b/packages/mcp-core/src/tools/catalog/get-event-attachment.ts
index 4527c7015..a50e971f6 100644
--- a/packages/mcp-core/src/tools/catalog/get-event-attachment.ts
+++ b/packages/mcp-core/src/tools/catalog/get-event-attachment.ts
@@ -117,8 +117,7 @@ export default defineTool({
       output += `**Type:** ${attachment.attachment.type}\n`;
       output += `**Size:** ${attachment.attachment.size} bytes\n`;
       output += `**MIME Type:** ${effectiveMimeType}\n`;
-      output += `**Created:** ${attachment.attachment.dateCreated}\n`;
-      output += `**SHA1:** ${attachment.attachment.sha1}\n\n`;
+      output += `**Created:** ${attachment.attachment.dateCreated}\n\n`;
       output += `**Download URL:** ${attachment.downloadUrl}\n\n`;
 
       if (isBinary) {
@@ -166,8 +165,7 @@ export default defineTool({
       output += `**Type:** ${attachment.type}\n`;
       output += `**Size:** ${attachment.size} bytes\n`;
       output += `**MIME Type:** ${attachment.mimetype}\n`;
-      output += `**Created:** ${attachment.dateCreated}\n`;
-      output += `**SHA1:** ${attachment.sha1}\n\n`;
+      output += `**Created:** ${attachment.dateCreated}\n\n`;
       output += "To download this attachment with the attachmentId provided:\n";
       output += `${formatToolCallInstruction({
         toolName: "get_event_attachment",
diff --git a/packages/mcp-server-mocks/src/fixtures/event-attachments.json b/packages/mcp-server-mocks/src/fixtures/event-attachments.json
index 7ce9f8a5f..d0d591052 100644
--- a/packages/mcp-server-mocks/src/fixtures/event-attachments.json
+++ b/packages/mcp-server-mocks/src/fixtures/event-attachments.json
@@ -6,7 +6,6 @@
     "size": 1024,
     "mimetype": "image/png",
     "dateCreated": "2025-04-08T21:15:04.000Z",
-    "sha1": "abc123def456",
     "headers": {
       "Content-Type": "image/png"
     }
diff --git a/packages/mcp-server-mocks/src/index.ts b/packages/mcp-server-mocks/src/index.ts
index 69bea77aa..e97c1757c 100644
--- a/packages/mcp-server-mocks/src/index.ts
+++ b/packages/mcp-server-mocks/src/index.ts
@@ -1607,7 +1607,6 @@ export const restHandlers = buildHandlers([
           size: 1024,
           mimetype: "application/octet-stream",
           dateCreated: "2025-04-08T21:15:04.000Z",
-          sha1: "abc123def456",
           headers: { "Content-Type": "application/octet-stream" },
         },
       ]),