From 01cbdcb8e4de17052260b464ec719f70487f89e0 Mon Sep 17 00:00:00 2001
From: "opencode-agent[bot]"
 <219766164+opencode-agent[bot]@users.noreply.github.com>
Date: Wed, 12 Aug 2026 00:18:50 -0500
Subject: [PATCH] fix(ai): batch Anthropic parallel tool results (#41948)

Co-authored-by: Aiden Cline <rekram1-node@users.noreply.github.com>
---
 .../ai/src/protocols/anthropic-messages.ts    |  5 +-
 .../test/provider/anthropic-messages.test.ts  | 89 +++++++++++++++++++
 2 files changed, 93 insertions(+), 1 deletion(-)

diff --git a/packages/ai/src/protocols/anthropic-messages.ts b/packages/ai/src/protocols/anthropic-messages.ts
index 7539e54d092..78c76be5e43 100644
--- a/packages/ai/src/protocols/anthropic-messages.ts
+++ b/packages/ai/src/protocols/anthropic-messages.ts
@@ -573,7 +573,10 @@ const lowerMessages = Effect.fn("AnthropicMessages.lowerMessages")(function* (
         cache_control: cacheControl(breakpoints, part.cache),
       })
     }
-    messages.push({ role: "user", content })
+    const previous = messages.at(-1)
+    if (previous?.role === "user" && previous.content.every((block) => block.type === "tool_result"))
+      messages[messages.length - 1] = { role: "user", content: [...previous.content, ...content] }
+    else messages.push({ role: "user", content })
   }
 
   return messages
diff --git a/packages/ai/test/provider/anthropic-messages.test.ts b/packages/ai/test/provider/anthropic-messages.test.ts
index ab1047f2c92..d8792c3d9df 100644
--- a/packages/ai/test/provider/anthropic-messages.test.ts
+++ b/packages/ai/test/provider/anthropic-messages.test.ts
@@ -271,6 +271,47 @@ describe("Anthropic Messages route", () => {
     }),
   )
 
+  it.effect("batches parallel tool results into one Anthropic user message", () =>
+    Effect.gen(function* () {
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model,
+          messages: [
+            Message.user("Check both cities."),
+            Message.assistant([
+              { type: "text", text: "I'll check both." },
+              ToolCallPart.make({ id: "call_paris", name: "weather", input: { city: "Paris" } }),
+              ToolCallPart.make({ id: "call_london", name: "weather", input: { city: "London" } }),
+            ]),
+            Message.tool({ id: "call_paris", name: "weather", result: { temperature: 22 } }),
+            Message.tool({ id: "call_london", name: "weather", result: { temperature: 18 } }),
+          ],
+          cache: "none",
+        }),
+      )
+
+      expect(prepared.body.messages).toMatchObject([
+        { role: "user", content: [{ type: "text", text: "Check both cities." }] },
+        {
+          role: "assistant",
+          content: [
+            { type: "text", text: "I'll check both." },
+            { type: "tool_use", id: "call_paris", name: "weather", input: { city: "Paris" } },
+            { type: "tool_use", id: "call_london", name: "weather", input: { city: "London" } },
+          ],
+        },
+        {
+          role: "user",
+          content: [
+            { type: "tool_result", tool_use_id: "call_paris", content: '{"temperature":22}' },
+            { type: "tool_result", tool_use_id: "call_london", content: '{"temperature":18}' },
+          ],
+        },
+      ])
+      expect(prepared.body.messages).toHaveLength(3)
+    }),
+  )
+
   it.effect("keeps tools and sends tool_choice none", () =>
     Effect.gen(function* () {
       const prepared = yield* compileRequest(
@@ -915,6 +956,54 @@ describe("Anthropic Messages route", () => {
     }),
   )
 
+  it.effect("assembles and persists multiple tool calls from one Anthropic response", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(request).pipe(
+        Effect.provide(
+          fixedResponse(
+            sseEvents(
+              { type: "message_start", message: { usage: { input_tokens: 5 } } },
+              {
+                type: "content_block_start",
+                index: 0,
+                content_block: { type: "tool_use", id: "call_paris", name: "weather", input: {} },
+              },
+              {
+                type: "content_block_delta",
+                index: 0,
+                delta: { type: "input_json_delta", partial_json: '{"city":"Paris"}' },
+              },
+              { type: "content_block_stop", index: 0 },
+              {
+                type: "content_block_start",
+                index: 1,
+                content_block: { type: "tool_use", id: "call_london", name: "weather", input: {} },
+              },
+              {
+                type: "content_block_delta",
+                index: 1,
+                delta: { type: "input_json_delta", partial_json: '{"city":"London"}' },
+              },
+              { type: "content_block_stop", index: 1 },
+              { type: "message_delta", delta: { stop_reason: "tool_use" }, usage: { output_tokens: 2 } },
+              { type: "message_stop" },
+            ),
+          ),
+        ),
+      )
+
+      expect(response.toolCalls).toMatchObject([
+        { id: "call_paris", name: "weather", input: { city: "Paris" } },
+        { id: "call_london", name: "weather", input: { city: "London" } },
+      ])
+      expect(response.message.content).toMatchObject([
+        { type: "tool-call", id: "call_paris", name: "weather", input: { city: "Paris" } },
+        { type: "tool-call", id: "call_london", name: "weather", input: { city: "London" } },
+      ])
+      expect(response.finishReason).toEqual({ normalized: "tool-calls", raw: "tool_use" })
+    }),
+  )
+
   it.effect("keeps malformed server tool input terminal", () =>
     Effect.gen(function* () {
       const body = sseEvents(