Flagship model lineup: GPT-5.4, Claude Sonnet 4.6, Gemini 3.1 Pro

As of early April, public flagship models included OpenAI's GPT-5.4 Thinking, Anthropic's Claude Sonnet 4.6, Google's Gemini 3.1 Pro, and xAI's Grok 4.20 Beta 2. No major release blitz occurred early April.