diff --git a/src/lib/api-client.ts b/src/lib/api-client.ts
index a23504f4..51da7f67 100644
--- a/src/lib/api-client.ts
+++ b/src/lib/api-client.ts
@@ -90,6 +90,7 @@ export {
 export {
   getDetailedTrace,
   listTransactions,
+  normalizeTraceSpan,
 } from "./api/traces.js";
 
 export {
diff --git a/src/lib/api/traces.ts b/src/lib/api/traces.ts
index 1b2cdfbe..0b8cc895 100644
--- a/src/lib/api/traces.ts
+++ b/src/lib/api/traces.ts
@@ -48,7 +48,24 @@ export async function getDetailedTrace(
       },
     }
   );
-  return data;
+  return data.map(normalizeTraceSpan);
+}
+
+/**
+ * The trace detail API (`/trace/{id}/`) returns each span's unique identifier
+ * as `event_id` rather than `span_id`. The value is the same 16-hex-char span
+ * ID that `parent_span_id` references on child spans. We copy it to `span_id`
+ * so the rest of the codebase can use a single, predictable field name.
+ */
+export function normalizeTraceSpan(span: TraceSpan): TraceSpan {
+  const normalized = { ...span };
+  if (!normalized.span_id && normalized.event_id) {
+    normalized.span_id = normalized.event_id;
+  }
+  if (normalized.children) {
+    normalized.children = normalized.children.map(normalizeTraceSpan);
+  }
+  return normalized;
 }
 
 /** Fields to request from the transactions API */
diff --git a/src/lib/formatters/human.ts b/src/lib/formatters/human.ts
index 765bd6e8..30442411 100644
--- a/src/lib/formatters/human.ts
+++ b/src/lib/formatters/human.ts
@@ -1122,6 +1122,8 @@ function formatSpanSimple(span: TraceSpan, opts: FormatSpanOptions): void {
     line += `  ${muted(`(${prettyMs(durationMs)})`)}`;
   }
 
+  line += `  ${muted(span.span_id ?? "")}`;
+
   lines.push(line);
 
   if (currentDepth < maxDepth) {
diff --git a/test/lib/api-client.normalize-trace-span.test.ts b/test/lib/api-client.normalize-trace-span.test.ts
new file mode 100644
index 00000000..41c66e04
--- /dev/null
+++ b/test/lib/api-client.normalize-trace-span.test.ts
@@ -0,0 +1,30 @@
+import { describe, expect, test } from "bun:test";
+import { normalizeTraceSpan } from "../../src/lib/api-client.js";
+
+describe("normalizeTraceSpan", () => {
+  test("copies event_id to span_id when span_id is missing", () => {
+    const span = { event_id: "abc123", start_timestamp: 0 } as Parameters<
+      typeof normalizeTraceSpan
+    >[0];
+    const result = normalizeTraceSpan(span);
+    expect(result.span_id).toBe("abc123");
+  });
+
+  test("preserves existing span_id", () => {
+    const result = normalizeTraceSpan({
+      span_id: "existing",
+      event_id: "other",
+      start_timestamp: 0,
+    });
+    expect(result.span_id).toBe("existing");
+  });
+
+  test("recurses into children", () => {
+    const result = normalizeTraceSpan({
+      span_id: "parent",
+      start_timestamp: 0,
+      children: [{ event_id: "child1", start_timestamp: 1 } as any],
+    });
+    expect(result.children?.[0]?.span_id).toBe("child1");
+  });
+});