diff --git a/cloud/db/traces.test.ts b/cloud/db/traces.test.ts
index 556a8911b2..660c783d6b 100644
--- a/cloud/db/traces.test.ts
+++ b/cloud/db/traces.test.ts
@@ -541,6 +541,69 @@ describe("Traces", () => {
       ),
     );
 
+    it.effect("rejects span when outbox insert fails", () =>
+      Effect.gen(function* () {
+        const db = yield* Database;
+
+        const resourceSpans = [
+          {
+            resource: { attributes: [] },
+            scopeSpans: [
+              {
+                scope: { name: "test" },
+                spans: [
+                  {
+                    traceId: "trace-outbox-error",
+                    spanId: "span-outbox-error",
+                    name: "test-span",
+                    startTimeUnixNano: "1000000000",
+                    endTimeUnixNano: "2000000000",
+                  },
+                ],
+              },
+            ],
+          },
+        ];
+
+        const result =
+          yield* db.organizations.projects.environments.traces.create({
+            userId: "owner-id",
+            organizationId: "org-id",
+            projectId: "project-id",
+            environmentId: "env-id",
+            data: { resourceSpans },
+          });
+
+        expect(result.rejectedSpans).toBe(1);
+        expect(result.acceptedSpans).toBe(0);
+      }).pipe(
+        Effect.provide(
+          new MockDrizzleORM()
+            .select([
+              {
+                role: "OWNER",
+                organizationId: "org-id",
+                memberId: "owner-id",
+                createdAt: new Date(),
+              },
+            ])
+            .select([
+              {
+                role: "OWNER",
+                organizationId: "org-id",
+                memberId: "owner-id",
+                createdAt: new Date(),
+              },
+            ])
+            .select([{ id: "project-id" }])
+            .insert([{ id: "trace-id" }]) // Trace upsert succeeds
+            .insert([{ id: "span-id" }]) // Span insert succeeds
+            .insert(new Error("Outbox insert failed")) // Outbox insert fails
+            .build(),
+        ),
+      ),
+    );
+
     it.effect("handles empty resourceSpans", () =>
       Effect.gen(function* () {
         const { environment, project, org, owner } =
diff --git a/cloud/db/traces.ts b/cloud/db/traces.ts
index 618a341e1b..09fd9b3a17 100644
--- a/cloud/db/traces.ts
+++ b/cloud/db/traces.ts
@@ -81,6 +81,7 @@ import {
   type CreateTraceResponse,
 } from "@/db/schema/traces";
 import { spans, type NewSpan } from "@/db/schema/spans";
+import { spansOutbox } from "@/db/schema/spansOutbox";
 import type { ProjectRole } from "@/db/schema";
 import type { ResourceSpans, KeyValue } from "@/api/traces.schemas";
 
@@ -419,6 +420,32 @@ export class Traces extends BaseAuthenticatedEffectService<
                   ),
                 );
 
+              // Write to outbox for ClickHouse sync (all inserted spans).
+              // This is intentionally not wrapped in a transaction so that
+              // a failed outbox write does not roll back the span insert.
+              // If the outbox insert fails we mark the span as rejected below.
+              if (insertedSpans.length > 0) {
+                const outboxRows = insertedSpans.map((s) => ({
+                  spanId: s.id,
+                  operation: "INSERT" as const,
+                }));
+                yield* client
+                  .insert(spansOutbox)
+                  .values(outboxRows)
+                  .onConflictDoNothing({
+                    target: [spansOutbox.spanId, spansOutbox.operation],
+                  })
+                  .pipe(
+                    Effect.mapError(
+                      (e) =>
+                        new DatabaseError({
+                          message: "Failed to write to outbox",
+                          cause: e,
+                        }),
+                    ),
+                  );
+              }
+
               return insertedSpans.length > 0;
             }).pipe(Effect.catchAll(() => Effect.succeed(false)));