From 03408fcecc05f918b3d6e9c613a12a18d2810eae Mon Sep 17 00:00:00 2001
From: Rick Blommers <rick@blommersit.nl>
Date: Tue, 23 Sep 2025 13:30:38 +0200
Subject: [PATCH 1/2] Filter out reasoning messages from Mistral

Mistral can return intermediate reasoning messages.
These caused `TypeError: no implicit conversion of Array
into String` when handling streamed responses.
This commit skips these messages to ensure
correct chunk handling. (Fixes #420)
---
 lib/ruby_llm/providers/mistral.rb             |  1 +
 lib/ruby_llm/providers/mistral/streaming.rb   | 30 ++++++++++++++++
 .../providers/mistral/streaming_spec.rb       | 36 +++++++++++++++++++
 3 files changed, 67 insertions(+)
 create mode 100644 lib/ruby_llm/providers/mistral/streaming.rb
 create mode 100644 spec/ruby_llm/providers/mistral/streaming_spec.rb

diff --git a/lib/ruby_llm/providers/mistral.rb b/lib/ruby_llm/providers/mistral.rb
index 18ddc266c..b67ef2656 100644
--- a/lib/ruby_llm/providers/mistral.rb
+++ b/lib/ruby_llm/providers/mistral.rb
@@ -7,6 +7,7 @@ class Mistral < OpenAI
       include Mistral::Chat
       include Mistral::Models
       include Mistral::Embeddings
+      include Mistral::Streaming
 
       def api_base
         'https://api.mistral.ai/v1'
diff --git a/lib/ruby_llm/providers/mistral/streaming.rb b/lib/ruby_llm/providers/mistral/streaming.rb
new file mode 100644
index 000000000..d94493211
--- /dev/null
+++ b/lib/ruby_llm/providers/mistral/streaming.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module RubyLLM
+  module Providers
+    class Mistral
+      # Streaming methods of the Misttral API integration
+      module Streaming
+        module_function
+
+        def build_chunk(data)
+          Chunk.new(
+            role: :assistant,
+            model_id: data['model'],
+            content: extract_content(data),
+            tool_calls: parse_tool_calls(data.dig('choices', 0, 'delta', 'tool_calls'), parse_arguments: false),
+            input_tokens: data.dig('usage', 'prompt_tokens'),
+            output_tokens: data.dig('usage', 'completion_tokens')
+          )
+        end
+
+        def extract_content(data)
+          data = data.dig('choices', 0, 'delta', 'content')
+          return '' if data.is_a?(Array) || data.is_a?(Hash)
+
+          data.to_s
+        end
+      end
+    end
+  end
+end
diff --git a/spec/ruby_llm/providers/mistral/streaming_spec.rb b/spec/ruby_llm/providers/mistral/streaming_spec.rb
new file mode 100644
index 000000000..497a7d853
--- /dev/null
+++ b/spec/ruby_llm/providers/mistral/streaming_spec.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe RubyLLM::Providers::Mistral::Streaming do
+  let(:test_obj) do
+    Object.new.extend(described_class).tap do |obj|
+      allow(obj).to receive(:parse_tool_calls).and_return([]) # ignore tool calls
+    end
+  end
+
+  it 'correctly processes content on receiving reasoning messages (an array in choices.delta.content)' do
+    data = {
+      'choices' => [{
+        'index' => 0,
+        'delta' => {
+          'content' => [{
+            'type' => 'thinking',
+            'thinking' => [{ 'type' => 'text', 'text' => 'Okay' }]
+          }]
+        }
+      }]
+    }
+    expect(test_obj.send(:build_chunk, data).content).to eq('')
+  end
+
+  it 'correctly processes content on receiving normal messages' do
+    data = {
+      'choices' => [{
+        'index' => 0,
+        'delta' => { 'content' => 'thecontent' }
+      }]
+    }
+    expect(test_obj.send(:build_chunk, data).content).to eq('thecontent')
+  end
+end

From 424644d732303ed02bf7a7c639d5f9efa04cd435 Mon Sep 17 00:00:00 2001
From: Rick Blommers <rick@blommersit.nl>
Date: Tue, 23 Sep 2025 13:44:10 +0200
Subject: [PATCH 2/2] Update streaming.rb (spelling error in comment)

---
 lib/ruby_llm/providers/mistral/streaming.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/ruby_llm/providers/mistral/streaming.rb b/lib/ruby_llm/providers/mistral/streaming.rb
index d94493211..3d2dd289a 100644
--- a/lib/ruby_llm/providers/mistral/streaming.rb
+++ b/lib/ruby_llm/providers/mistral/streaming.rb
@@ -3,7 +3,7 @@
 module RubyLLM
   module Providers
     class Mistral
-      # Streaming methods of the Misttral API integration
+      # Streaming methods of the Mistral API integration
       module Streaming
         module_function