Add Anthropic structured output support

docs/_core_features/chat.md

@@ -534,7 +534,7 @@ end
 
 Not all models support structured output. Currently supported:
 - **OpenAI**: GPT-4o, GPT-4o-mini, and newer models
-- **Anthropic**: No native structured output support. You can simulate it with tool definitions or careful prompting
+- **Anthropic**: Claude 4.5+ models (Haiku, Sonnet, Opus)
 - **Gemini**: Gemini 1.5 Pro/Flash and newer
 
 Models that don't support structured output:

lib/ruby_llm/providers/anthropic/capabilities.rb

@@ -31,11 +31,20 @@ def supports_vision?(model_id)
         end
 
         def supports_functions?(model_id)
-          model_id.match?(/claude-3/)
+          !model_id.match?(/claude-[12]/)
         end
 
         def supports_json_mode?(model_id)
-          model_id.match?(/claude-3/)
+          !model_id.match?(/claude-[12]/)
+        end
+
+        def supports_structured_output?(model_id)
+          match = model_id.match(/claude-(?:sonnet|opus|haiku)-(\d+)-(\d+)/)
+          return false unless match
+
+          major = match[1].to_i
+          minor = match[2].to_i
+          major > 4 || (major == 4 && minor >= 5)
         end
 
         def supports_extended_thinking?(model_id)
@@ -92,12 +101,13 @@ def modalities_for(model_id)
         def capabilities_for(model_id)
           capabilities = ['streaming']
 
-          if model_id.match?(/claude-3/)
+          unless model_id.match?(/claude-[12]/)
             capabilities << 'function_calling'
             capabilities << 'batch'
           end
 
-          capabilities << 'reasoning' if model_id.match?(/claude-3-7|-4/)
+          capabilities << 'structured_output' if supports_structured_output?(model_id)
+          capabilities << 'reasoning' if model_id.match?(/claude-3-7-sonnet|claude-(?:sonnet|opus|haiku)-4/)
           capabilities << 'citations' if model_id.match?(/claude-3\.5|claude-3-7/)
           capabilities
         end

lib/ruby_llm/providers/anthropic/chat.rb

@@ -11,12 +11,12 @@ def completion_url
           'v1/messages'
         end
 
-        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil, thinking: nil) # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument
+        def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil, thinking: nil) # rubocop:disable Metrics/ParameterLists
           system_messages, chat_messages = separate_messages(messages)
           system_content = build_system_content(system_messages)
 
           build_base_payload(chat_messages, model, stream, thinking).tap do |payload|
-            add_optional_fields(payload, system_content:, tools:, temperature:)
+            add_optional_fields(payload, system_content:, tools:, temperature:, schema:)
           end
         end
 
@@ -59,10 +59,18 @@ def build_base_payload(chat_messages, model, stream, thinking)
           payload
         end
 
-        def add_optional_fields(payload, system_content:, tools:, temperature:)
+        def add_optional_fields(payload, system_content:, tools:, temperature:, schema: nil)
           payload[:tools] = tools.values.map { |t| Tools.function_for(t) } if tools.any?
           payload[:system] = system_content unless system_content.empty?
           payload[:temperature] = temperature unless temperature.nil?
+          payload[:output_config] = build_output_config(schema) if schema
+        end
+
+        def build_output_config(schema)
+          normalized = RubyLLM::Utils.deep_dup(schema)
+          normalized.delete(:strict)
+          normalized.delete('strict')
+          { format: { type: 'json_schema', schema: normalized } }
         end
 
         def parse_completion_response(response)