machine learning machine learning deployment From GPT-5.5 to DeepSeek V4: How Developers Are Building Smarter AI Agents with Multi-Model Routing in 2026 – AiThority Google Inc. April 27, 2026 April 27, 2026 From GPT-5.5 to DeepSeek V4: How Developers Are Building Smarter AI Agents with Multi-Model Routing in 2026 AiThority