Gemini CLI and Codex are both open-source terminal coding agents, and the choice is a clean trade between cost and benchmarks. Gemini CLI is free-and-Gemini. Codex runs GPT-5.5, which leads the public coding benchmarks.
Summary
| Dimension | Gemini CLI | Codex |
|---|---|---|
| Model | Gemini (free tier) | GPT-5.5 |
| SWE-bench Verified | Competitive | 88.7% (lead) |
| Terminal-Bench 2.0 | Competitive | 82.7% (lead) |
| Cost | Free tier, then API | Subscription / API |
| License | Open source (Google) | Apache-2.0 (OpenAI) |
| Best for | Cheap capable coding | Top benchmark performance |
Free vs Benchmarks
Gemini CLI's case is cost and context. Its free tier makes it one of the cheapest capable terminal agents, and it leans on Gemini's long-context strength for large codebases. If Gemini models meet your needs, you may pay nothing.
Codex's case is performance. Running GPT-5.5, it holds the top public coding scores: 88.7% SWE-bench Verified and 82.7% Terminal-Bench 2.0. It also shipped subagents to GA for parallel work. For maximum coding accuracy and terminal-heavy workflows, Codex leads. See the full Codex vs Claude Code breakdown.
Where Gemini CLI Wins
Generous free tier
One of the cheapest ways to run a capable coding agent.
Long-context strength
Leans on Gemini's long context for large codebases.
Google backing
Maintained by Google with steady updates.
Where Codex Wins
Top coding benchmarks
GPT-5.5 leads SWE-bench Verified (88.7%) and Terminal-Bench (82.7%).
Subagents GA
Run up to 8 parallel agents from one task.
Rust-native, Apache-2.0
Fast CLI, fully open source.
Decision Framework
| Your priority | Best choice | Why |
|---|---|---|
| Lowest cost | Gemini CLI | Generous free Gemini tier. |
| Top coding accuracy | Codex | GPT-5.5 leads benchmarks. |
| Terminal-heavy work | Codex | 82.7% Terminal-Bench. |
| Large-codebase context | Gemini CLI | Gemini long context, free. |
| Parallel agents | Codex | Subagents GA, 8 parallel. |
Frequently Asked Questions
Is Gemini CLI or Codex better?
Gemini CLI for cheapest capable coding; Codex for top benchmark performance on GPT-5.5.
Is Gemini CLI free?
It has a generous free Gemini tier. Codex is free software but runs paid OpenAI models.
Which has better benchmarks?
Codex/GPT-5.5 leads SWE-bench Verified (88.7%) and Terminal-Bench (82.7%).
Are both open source?
Yes. Codex is Apache-2.0; Gemini CLI is open source from Google.
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