diff --git a/dist/acp-agent.js b/dist/acp-agent.js
--- a/dist/acp-agent.js
+++ b/dist/acp-agent.js
@@ -2681,10 +2681,20 @@
                                         cost: {
                                             amount: message.total_cost_usd,
                                             currency: "USD",
                                         },
-                                        ...(message.origin && {
-                                            _meta: { "_claude/origin": message.origin },
-                                        }),
+                                        _meta: {
+                                            ...(message.origin && { "_claude/origin": message.origin }),
+                                            // ACP's core Usage shape exposes context occupancy and
+                                            // cost, but not the billable input/output split. Keep the
+                                            // SDK's bounded aggregate in extension metadata so ACPX can
+                                            // normalize it without persisting a raw provider message.
+                                            usage: {
+                                                input_tokens: message.usage.input_tokens,
+                                                output_tokens: message.usage.output_tokens,
+                                                cache_read_input_tokens: message.usage.cache_read_input_tokens,
+                                                cache_creation_input_tokens: message.usage.cache_creation_input_tokens,
+                                            },
+                                        },
                                     },
                                 });
                             }