From d6cac314e67466b17d3e2ecca3cc440d38fdf2f9 Mon Sep 17 00:00:00 2001
From: tsushanth <78000697+tsushanth@users.noreply.github.com>
Date: Thu, 11 Jun 2026 09:17:31 -0700
Subject: [PATCH] fix(ai-amazon-bedrock): emit streaming "finish" after
 metadata arrives
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Closes #6237.

The Bedrock Converse stream sends `metadata` (with the populated `usage`
block) AFTER `messageStop`, but the SDK was emitting `"finish"`
synchronously on `messageStop`, capturing the still-empty
`{ inputTokens: undefined, outputTokens: undefined, totalTokens: undefined }`
defaults. The caller's terminal stream event always saw
`usage.inputTokens === undefined` / `usage.outputTokens === undefined`.

Buffer the finish reason on `messageStop`, then emit `"finish"` from the
`metadata` case once `usage`, `cacheWriteInputTokens`, and `trace` are
populated. Output payload shape (reason / usage / metadata.bedrock) is
unchanged; only the timing moves.

I didn't add a streaming test — `converseStream` is `null as any` in the
existing test harness in `AmazonBedrockLanguageModel.test.ts`, so there's
no pattern to mock `ConverseResponseStreamEvent` against yet. Happy to
follow up with a focused stream test once the maintainers point at the
preferred mocking shape.
---
 .changeset/fix-bedrock-streaming-usage.md     |  5 +++
 .../src/AmazonBedrockLanguageModel.ts         | 33 +++++++++++++------
 2 files changed, 28 insertions(+), 10 deletions(-)
 create mode 100644 .changeset/fix-bedrock-streaming-usage.md

diff --git a/.changeset/fix-bedrock-streaming-usage.md b/.changeset/fix-bedrock-streaming-usage.md
new file mode 100644
index 00000000000..879d268c534
--- /dev/null
+++ b/.changeset/fix-bedrock-streaming-usage.md
@@ -0,0 +1,5 @@
+---
+"@effect/ai-amazon-bedrock": patch
+---
+
+Fix `@effect/ai-amazon-bedrock` streaming so the terminal `"finish"` part carries real token counts. The Bedrock Converse stream sends `metadata` (with the populated `usage` block) **after** `messageStop`, but the SDK was emitting `"finish"` synchronously on `messageStop`, capturing the still-empty `usage` defaults. Buffer the finish reason on `messageStop` and emit `"finish"` from the `metadata` case once `inputTokens` / `outputTokens` / `totalTokens` are filled in.
diff --git a/packages/ai/amazon-bedrock/src/AmazonBedrockLanguageModel.ts b/packages/ai/amazon-bedrock/src/AmazonBedrockLanguageModel.ts
index 72e87f4c08d..1c24e0d1f4c 100644
--- a/packages/ai/amazon-bedrock/src/AmazonBedrockLanguageModel.ts
+++ b/packages/ai/amazon-bedrock/src/AmazonBedrockLanguageModel.ts
@@ -656,6 +656,7 @@ const makeStreamResponse: (
 
     let trace: ConverseTrace | undefined = undefined
     let cacheWriteInputTokens: number | undefined = undefined
+    let finishReason: Response.FinishReason | undefined = undefined
     const usage: Mutable<typeof Response.Usage.Encoded> = {
       inputTokens: undefined,
       outputTokens: undefined,
@@ -677,16 +678,12 @@ const makeStreamResponse: (
           }
 
           case "messageStop": {
-            const reason = InternalUtilities.resolveFinishReason(event.messageStop.stopReason)
-            parts.push({
-              type: "finish",
-              reason,
-              usage,
-              metadata: {
-                bedrock: { trace, usage: { cacheWriteInputTokens } }
-              }
-            })
-
+            // Buffer the finish reason — the Bedrock Converse stream sends
+            // `metadata` (with usage / cache / trace) AFTER `messageStop`,
+            // so emitting the `"finish"` part here would leak the empty
+            // `usage` defaults from the case below to the caller. Wait for
+            // `metadata` to land and emit `"finish"` there.
+            finishReason = InternalUtilities.resolveFinishReason(event.messageStop.stopReason)
             break
           }
 
@@ -908,6 +905,22 @@ const makeStreamResponse: (
             if (Predicate.isNotUndefined(event.metadata.trace)) {
               trace = event.metadata.trace
             }
+            // Bedrock sends `metadata` after `messageStop`, so by the time
+            // we land here we have both the finish reason (buffered above)
+            // and the populated usage / cache / trace. Emit the `"finish"`
+            // part now so the caller sees real token counts on the
+            // terminal stream event.
+            if (Predicate.isNotUndefined(finishReason)) {
+              parts.push({
+                type: "finish",
+                reason: finishReason,
+                usage,
+                metadata: {
+                  bedrock: { trace, usage: { cacheWriteInputTokens } }
+                }
+              })
+              finishReason = undefined
+            }
             break
           }