Add configurable Anthropic API base URL

Introduces anthropic_api_base configuration option to allow users to specify custom Anthropic API endpoints. This enables support for proxies, custom deployments, and alternative Anthropic-compatible services. Also fixes URL path formatting in chat and models endpoints by removing redundant leading slashes.

Author: ericproulx

bin/console

@@ -9,6 +9,7 @@ require 'irb'
 
 RubyLLM.configure do |config|
   config.anthropic_api_key = ENV.fetch('ANTHROPIC_API_KEY', nil)
+  config.anthropic_api_base = ENV.fetch('ANTHROPIC_BASE_URL', nil)
   config.bedrock_api_key = ENV.fetch('AWS_ACCESS_KEY_ID', nil)
   config.bedrock_region = ENV.fetch('AWS_REGION', nil)
   config.bedrock_secret_key = ENV.fetch('AWS_SECRET_ACCESS_KEY', nil)

lib/ruby_llm/configuration.rb

@@ -8,6 +8,7 @@ class Configuration
                   :openai_organization_id,
                   :openai_project_id,
                   :openai_use_system_role,
+                  :anthropic_api_base,
                   :anthropic_api_key,
                   :gemini_api_key,
                   :gemini_api_base,

lib/ruby_llm/providers/anthropic.rb

@@ -12,7 +12,7 @@ class Anthropic < Provider
       include Anthropic::Tools
 
       def api_base
-        'https://api.anthropic.com'
+        @config.anthropic_api_base || 'https://api.anthropic.com'
       end
 
       def headers

lib/ruby_llm/providers/anthropic/chat.rb

@@ -8,7 +8,7 @@ module Chat
         module_function
 
         def completion_url
-          '/v1/messages'
+          'v1/messages'
         end
 
         def render_payload(messages, tools:, temperature:, model:, stream: false, schema: nil, thinking: nil) # rubocop:disable Metrics/ParameterLists,Lint/UnusedMethodArgument

lib/ruby_llm/providers/anthropic/models.rb

@@ -8,7 +8,7 @@ module Models
         module_function
 
         def models_url
-          '/v1/models'
+          'v1/models'
         end
 
         def parse_list_models_response(response, slug, capabilities)

spec/ruby_llm/providers/anthropic_spec.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe RubyLLM::Providers::Anthropic do
+  subject(:provider) { described_class.new(config) }
+
+  let(:config) do
+    instance_double(
+      RubyLLM::Configuration,
+      request_timeout: 300,
+      max_retries: 3,
+      retry_interval: 0.1,
+      retry_interval_randomness: 0.5,
+      retry_backoff_factor: 2,
+      http_proxy: nil,
+      anthropic_api_key: 'test-key',
+      anthropic_api_base: anthropic_api_base
+    )
+  end
+
+  describe '#api_base' do
+    context 'when anthropic_api_base is not set' do
+      let(:anthropic_api_base) { nil }
+
+      it 'returns the default Anthropic API URL' do
+        expect(provider.api_base).to eq('https://api.anthropic.com')
+      end
+    end
+
+    context 'when anthropic_api_base is set' do
+      let(:anthropic_api_base) { 'https://custom-anthropic-endpoint.example.com' }
+
+      it 'returns the custom API URL' do
+        expect(provider.api_base).to eq('https://custom-anthropic-endpoint.example.com')
+      end
+    end
+  end
+end