From 1cefa749aa7b0cd3e330a95f0b03e98dc0a914bd Mon Sep 17 00:00:00 2001
From: Alfredo Matas <amatas@gmail.com>
Date: Fri, 27 Mar 2026 19:28:34 +0100
Subject: [PATCH] model/parsers: close think block if tool block starts in
 Qwen3.5 (#15022)

---
 model/parsers/qwen35.go      |  9 +++++++++
 model/parsers/qwen35_test.go | 22 ++++++++++++++--------
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/model/parsers/qwen35.go b/model/parsers/qwen35.go
index b3e672c5d..6a6f54b69 100644
--- a/model/parsers/qwen35.go
+++ b/model/parsers/qwen35.go
@@ -21,6 +21,7 @@ const (
 const (
 	qwen35ThinkingOpenTag  = "<think>"
 	qwen35ThinkingCloseTag = "</think>"
+	qwen35ToolCallOpenTag  = "<tool_call>"
 )
 
 // Qwen35Parser handles qwen3.5 reasoning extraction and delegates post-thinking
@@ -202,6 +203,14 @@ func (p *Qwen35Parser) eat() ([]qwen35Event, bool) {
 				events = append(events, qwen35EventThinkingContent{content: unambiguous})
 			}
 			return events, false
+		} else if strings.Contains(acc, qwen35ToolCallOpenTag) {
+			// qwen3.5:9b model forgets sometimes to use </think> tag before the <tool_call> block starts
+			// this condition ends the Think block and continues with the <tool_call> when the tag
+			// is found
+			thinking, tooling := p.splitAtTag(qwen35ToolCallOpenTag, true)
+			p.buffer.Reset()
+			p.buffer.WriteString(thinking + qwen35ThinkingCloseTag + qwen35ToolCallOpenTag + tooling)
+			return events, true
 		}
 
 		whitespaceLen := trailingWhitespaceLen(acc)
diff --git a/model/parsers/qwen35_test.go b/model/parsers/qwen35_test.go
index 94a3f26fe..abedfe8f4 100644
--- a/model/parsers/qwen35_test.go
+++ b/model/parsers/qwen35_test.go
@@ -108,7 +108,7 @@ func TestQwen35ParserAssistantPrefillStartsInContent(t *testing.T) {
 	}
 }
 
-func TestQwen35ParserToolCallEmittedInThinkingIsNotParsed(t *testing.T) {
+func TestQwen35ParserToolCallEmittedInThinkingIsParsed(t *testing.T) {
 	parser := ParserForName("qwen3.5")
 	if parser == nil {
 		t.Fatal("expected qwen3.5 parser")
@@ -141,14 +141,20 @@ SF
 	if content != "" {
 		t.Fatalf("expected empty content, got %q", content)
 	}
-	expectedThinking := `Need weather lookup<tool_call><function=get_weather><parameter=location>
-SF
-</parameter></function></tool_call>`
-	if thinking != expectedThinking {
-		t.Fatalf("expected thinking %q, got %q", expectedThinking, thinking)
+	if thinking != "Need weather lookup" {
+		t.Fatalf("expected thinking %q, got %q", "Need weather lookup", thinking)
 	}
-	if len(calls) != 0 {
-		t.Fatalf("expected no tool calls before </think>, got %d", len(calls))
+	if len(calls) != 1 {
+		t.Fatalf("expected 1 tool call, got %d", len(calls))
+	}
+
+	if calls[0].Function.Name != "get_weather" {
+		t.Fatalf("expected tool name %q, got %q", "get_weather", calls[0].Function.Name)
+	}
+
+	location, ok := calls[0].Function.Arguments.Get("location")
+	if !ok || location != "SF" {
+		t.Fatalf("expected location %q, got %v", "SF", location)
 	}
 }