Major Large Language Models (LLMs)

Developed by U.S.-Based Companies (As of October 2025)

A curated list of flagship releases and key details from major developers like OpenAI, Anthropic, Google, Meta, xAI, and Microsoft.

Developer (HQ)	Key LLMs	Notable Features/Strengths	Access
OpenAI (San Francisco, CA)	GPT-5 (released Aug 2025) GPT-4.5 (released Feb 2025) GPT-4o (ongoing updates) O3 series (e.g., O3-mini-high)	Advanced multimodal reasoning, long-term memory (up to 128K tokens), reduced hallucinations (26% lower than GPT-4o), proactive dialogue. Excels in logic, planning, and real-time tasks.	API via OpenAI platform; free tier with limits; Pro access for advanced models.
Anthropic (San Francisco, CA)	Claude 4 Opus (released May 2025) Claude 4 Sonnet (released May 2025) Claude 3.7 Haiku	Agentic workflows, extended thinking with tool-use, 1M token context window. Tops in coding (42% market share), research, and safe enterprise use (helpful, honest, harmless).	API; integrated in tools like Slack/Notion; enterprise focus.
Google DeepMind (Mountain View, CA)	Gemini 2.5 Pro (released Mar 2025) Gemini 2.0 Flash (released Feb 2025) Gemma 3 (open-weight, 1B-27B params)	"Deep Think" step-by-step reasoning, multimodal (text/image/code), real-time search. Strong in coding, global/multilingual tasks; Gemma for local/on-device use.	Google Vertex AI/API; free for Gemma downloads.
Meta AI (Menlo Park, CA)	Llama 4 (released Apr 2025; Scout/Maverick variants) Llama 3 (ongoing fine-tunes; 8B-70B params)	Open-source, natively multimodal, mixture-of-experts (MoE) architecture. Prioritizes efficiency, fine-tuning for chatbots/content; supports 50+ languages.	Hugging Face/GitHub downloads; free for research/commercial use (with license).
xAI (San Francisco, CA)	Grok 4 (latest flagship) Grok 3 (released Feb 2025) Grok Code Fast 1	Real-time X (Twitter) integration, sarcastic/humorous tone, advanced problem-solving/education. Balances speed/quality; excels in coding and current events analysis.	xAI API/grok.com; free limited access via X apps.
Microsoft (Redmond, WA)	Phi-4 series (late 2024/early 2025) Turing-NLG (legacy)	Small/efficient models (under MIT license), strong in math/coding/text generation. Focus on on-device/edge AI; integrated with Azure for enterprise.	Azure AI Studio; open-source downloads for Phi.

Key Notes & Trends in 2025

**Trends**: U.S. LLMs emphasize **agentic capabilities** (multi-step reasoning/tools), **multimodal inputs** (text+images/audio), and **efficiency** (smaller models like Phi/Gemma matching larger ones).
**Access**: **Open-source** options from Meta/Google democratize access, while proprietary ones from OpenAI/Anthropic lead in performance benchmarks.
**Exclusions**: This list focuses on U.S.-based flagships. Models from non-U.S. entities (e.g., Mistral, DeepSeek) and legacy models (e.g., GPT-3, BERT) are not included.
**Total Count**: The models listed represent the core of the current LLM landscape, powering essential tools like ChatGPT and Gemini.

This landscape evolves rapidly; for the latest benchmarks, check sources like Hugging Face or LMSYS Arena.