# AI assistants & models: the tools companies use 509 companies on usedby use a tool of its 4 categories with a public customer. Each category ranks its own tools: tools of different jobs are not ranked against each other. Counts are of companies on usedby, not of the whole market. Latest check 2026-10-14: 496 of 595 public lines checked. > General AI assistants, the models and APIs behind them, AI answer engines and the company-wide platforms that build AI agents. ## Categories - [Enterprise AI platforms](https://www.usedby.ai/tools/category/enterprise-ai-platforms.md): 250 companies, 9 tools with a public customer; most used: Writer - [AI assistants](https://www.usedby.ai/tools/category/ai-assistants.md): 121 companies, 4 tools with a public customer; most used: Claude - [AI search & research](https://www.usedby.ai/tools/category/ai-search-research.md): 120 companies, 7 tools with a public customer; most used: Listen - [Foundation models & model APIs](https://www.usedby.ai/tools/category/foundation-models-llms.md): 70 companies, 4 tools with a public customer; most used: Mistral --- Source: https://www.usedby.ai/tools/category/ai-assistants-models ยท How we check: https://www.usedby.ai/methodology