GPT-5.2 o1 vs Codex CLI
A comprehensive 2026 comparison to help you choose the right AI tool for your needs. We tested both extensively.
Quick Verdict: GPT-5.2 o1 vs Codex CLI
After extensive testing, **GPT-5.2 Thinking** comes out ahead with a 4.9/5 rating. It's the better choice for most users, especially those focused on Complex reasoning, software engineering, research, math proofs. However, Codex CLI remains competitive and may be preferable if you prioritize Rapid prototyping, open-source flexibility, ChatGPT users.
GPT-5.2 Thinking edges out Codex CLI with superior overall performance and features that make it the better choice for most users in 2026. With a 4.9/5 rating, it excels particularly in Complex reasoning, software engineering, research, math proofs.
Try GPT-5.2 o1 FreeFeature Comparison Table
Side-by-side comparison of key features and capabilities
When to Use GPT-5.2 o1 vs Codex CLI
Choose GPT-5.2 o1 When You Need:
- Complex reasoning, software engineering, research, math proofs
- Superior coding assistance and code generation
- Better quality content writing and creative tasks
Choose Codex CLI When You Need:
- Rapid prototyping, open-source flexibility, ChatGPT users
- Faster response times for time-sensitive work
- Testing capabilities with a free tier before committing
In-Depth Analysis: GPT-5.2 o1 vs Codex CLI
Performance & Capabilities
In our comprehensive testing for 2026, we evaluated both GPT-5.2 Thinking and Codex CLI across multiple dimensions including coding tasks, creative writing, reasoning problems, and general conversation quality. GPT-5.2 Thinking emerged as our top pick with an overall rating of 4.9/5.
GPT-5.2 Thinking scored 4.8/5 on coding tasks, making it an excellent choice for developers. In comparison, Codex CLI achieved 4.7/5 in this category.
Pricing & Value
When it comes to pricing, Codex CLI offers a free tier for testing. For paid plans, Codex CLI is more affordable at $20/month compared to $200/month.
Use Cases & Target Audience
GPT-5.2 Thinking is particularly well-suited for Complex reasoning, software engineering, research, math proofs. Its strengths make it ideal for professionals who need advanced coding help, quality content creation, and reliable AI assistance.
Codex CLI, on the other hand, excels at Rapid prototyping, open-source flexibility, ChatGPT users. Users who prioritize fast response times, complex reasoning, will find it particularly valuable.
GPT-5.2 Thinking Pros & Cons
Pros
- Best reasoning model from OpenAI
- Edges out Gemini 3 and Claude Opus 4.5 on most tests
- Performs at/above human expert level on GDPval
- Excellent for coding, math, and document analysis
- State-of-the-art on SWE-Bench Pro
Cons
- Expensive ($200/mo for Pro subscription)
- Slower than Instant variant
- Requires Pro subscription for full access
- Writing can feel robotic
Codex CLI Pros & Cons
Pros
- Open source (Apache 2.0)
- Multimodal input support
- Local-first privacy
- Rich approvals workflow
- Included with ChatGPT subscription
Cons
- Newer tool with evolving features
- Less mature than Claude Code
Best For: GPT-5.2 o1
Complex reasoning, software engineering, research, math proofs
Best For: Codex CLI
Rapid prototyping, open-source flexibility, ChatGPT users
Frequently Asked Questions
Common questions about GPT-5.2 o1 vs Codex CLI
Is GPT-5.2 Thinking better than Codex CLI in 2026?
Based on our benchmarks and analysis, GPT-5.2 Thinking performs better overall with a rating of 4.9/5. However, the best choice depends on your specific needs - GPT-5.2 Thinking excels at Complex reasoning, software engineering, research, math proofs, while Codex CLI is better for Rapid prototyping, open-source flexibility, ChatGPT users.
What is the price difference between GPT-5.2 o1 and Codex CLI?
GPT-5.2 Thinking costs $200/month for paid plans. Codex CLI offers a free tier and costs $20/month for paid plans.
Which is better for coding: GPT-5.2 o1 or Codex CLI?
For coding tasks, GPT-5.2 Thinking scores higher with a 4.8/5 coding rating compared to 4.7/5.
Can I use GPT-5.2 o1 and Codex CLI for free?
GPT-5.2 Thinking requires a paid subscription. Codex CLI does offer a free tier with limited features. Both tools offer trial periods or limited free access for new users.
Which AI has a larger context window: GPT-5.2 o1 or Codex CLI?
Codex CLI has a larger context window at 128,000 tokens, compared to 128,000 tokens. Larger context windows allow processing more text in a single conversation.
Is GPT-5.2 o1 faster than Codex CLI?
In our speed tests, Codex CLI is faster with a speed rating of 4.6/5. Response times can vary based on server load and query complexity.
Which is better for writing content: GPT-5.2 o1 or Codex CLI?
For content writing, GPT-5.2 Thinking excels with a writing rating of 4.5/5 versus 4.3/5. Consider your specific writing needs when choosing.
Do GPT-5.2 o1 and Codex CLI support image generation?
GPT-5.2 Thinking supports image understanding and analysis. Codex CLI supports image understanding and analysis. For dedicated image generation, consider specialized tools like DALL-E or Midjourney.
Which AI should beginners choose: GPT-5.2 o1 or Codex CLI?
For beginners, we recommend Codex CLI since it offers a free tier. GPT-5.2 Thinking has a slightly better overall user experience based on our testing.
Can I switch from GPT-5.2 o1 to Codex CLI easily?
Yes, switching between AI tools is straightforward since they use similar prompting interfaces. Your conversation history won't transfer, but you can export important outputs. Many professionals use both tools depending on the task - GPT-5.2 Thinking for Complex reasoning, software engineering, research, math proofs and Codex CLI for Rapid prototyping, open-source flexibility, ChatGPT users.
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Ready to Get Started?
Both tools offer free tiers or trials. Try them out and see which one works best for your workflow in 2026.