Gemini CLI vs Codex CLI: Google vs OpenAI Terminal Agents (2026)

+ Gemini CLI

• +Massive 1M token context window processes entire large codebases
• +Broad multimodal input: text, images, audio, and video
• +MCP support for connecting external tools and data sources
• +Generous free tier with no upfront cost to get started
• +Strong performance on code understanding and generation tasks
• +Google ecosystem integration potential for cloud-native workflows

+ Codex CLI

• +Sandboxed execution with network disabled provides strong safety defaults
• +Access to OpenAI reasoning models (o3, o4) for complex logic tasks
• +Multiple execution modes from suggest-only to full autonomy
• +Auto-creates git commits for every change with descriptive messages
• +Familiar for developers already in the OpenAI ecosystem
• +Granular control over agent autonomy level

Gemini CLI and Codex CLI are terminal-based AI coding agents from Google and OpenAI respectively. Both are open source under Apache 2.0 and represent each company's vision for agentic coding in the terminal. They compete directly with each other and with Anthropic's Claude Code, making this a three-way race for the best CLI coding agent.

Gemini CLI's headline feature is its 1M token context window. This means it can load and reason about entire large codebases in a single context, reducing the need for chunking or retrieval strategies. It also accepts multimodal input (images, audio, video), which is useful for tasks like implementing designs from screenshots or processing media files. Gemini CLI has MCP support, giving it extensibility that Codex CLI lacks. Codex CLI's standout feature is its sandboxed execution model. By default, it runs in a sandbox with network access disabled, which prevents the agent from making unintended API calls, downloading packages, or exfiltrating data. This makes Codex CLI safer for sensitive codebases. Codex CLI also offers three distinct execution modes: suggest (just shows proposed changes), auto-edit (applies changes automatically), and full-auto (applies changes and runs commands), giving developers fine-grained control over autonomy. Its access to OpenAI's reasoning models (o3, o4) is an advantage for tasks requiring complex logical reasoning.

Choose Gemini CLI if you need a massive context window, multimodal input, MCP extensibility, or want to start free. Choose Codex CLI if you prioritize sandboxed safety, want access to OpenAI's reasoning models, or need granular control over agent autonomy. Both are solid open-source tools that are improving rapidly.