GPT-5.1 vs GPT-5 Codex
Compare pricing, context windows, and strengths for GPT-5.1 by OpenAI and GPT-5 Codex by OpenAI - and see how to put either to work in Appaca.
GPT-5.1
Flagship model for coding, reasoning, and agentic tasks with adjustable reasoning depth and multimodal input/output.
View GPT-5.1GPT-5 Codex
Version of GPT-5 optimized for agentic coding tasks in Codex, offering strong reasoning, reliable code generation, and long-context project understanding.
View GPT-5 CodexGPT-5.1 vs GPT-5 Codex at a glance
Specs and pricing side by side, from the Appaca AI models directory.
| Spec | GPT-5.1 | GPT-5 Codex |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Model type | Text | Text |
| Context window | 400K tokens | 400K tokens |
| Input price | $1.25 / 1M tokens | $1.25 / 1M tokens |
| Output price | $10 / 1M tokens | $10 / 1M tokens |
| Status | Current | Superseded by GPT-5.1 Codex |
How GPT-5.1 and GPT-5 Codex differ
What the numbers mean in practice when choosing between GPT-5.1 and GPT-5 Codex.
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Both models cost the same on input: $1.25 per million tokens.
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Both models offer the same 400K tokens context window.
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GPT-5 Codex has been superseded by GPT-5.1 Codex - for new builds, consider the newer model first.
Strengths side by side
Where each model shines, according to benchmarks and provider positioning.
GPT-5.1
1. Configurable Reasoning for Agentic Tasks
- Built to excel in autonomous or semi-autonomous coding workflows, with adjustable reasoning effort for planning, refactoring and debugging.
2. Fast Multi-Modal Input with Large Output
- Accepts both text and image inputs while producing text outputs.
- Offers up to 128 k output tokens, allowing long responses and code generation across multiple files.
3. Large Context & Knowledge Cut-Off
- 400 k token context window supports processing large codebases or documents.
- Knowledge cut-off of Sep 30 2024 ensures familiarity with recent tools and frameworks.
4. Reasoning Token Support
- Provides explicit support for reasoning tokens, enabling developers to fine-tune the balance between reasoning depth and speed.
GPT-5 Codex
1. Purpose-Built for Agentic Coding
- Optimized specifically for scenarios where the model must act as an autonomous or semi-autonomous coding agent.
- Tailored for Codex workflows such as planning, editing, debugging, and multi-step tool-driven code tasks.
2. Advanced Coding Reasoning
- Extends GPT-5's higher reasoning mode to better handle complex software logic and multi-file dependencies.
- Produces more accurate, structured, and maintainable code across modern programming languages.
3. Strong Tool Use in Developer-Like Environments
- Designed for Codex's agent environment, enabling the model to:
- Read and modify files
- Follow function signatures and API contracts
- Navigate codebases with awareness of context and structure
4. Large Context Window for Full-Project Understanding
- 400,000-token context allows ingestion of:
- Entire repositories
- Multiple files at once
- Architectural descriptions
- Enables long-range reasoning across codebases rather than isolated snippets.
5. Multimodal Capability for Development Tasks
- Accepts text and image as input (great for screenshots of error logs, UI mocks, whiteboards).
- Outputs text only, focusing its output precision on code, reasoning, and documentation.
6. Continuous Snapshot Updates
- The underlying model version is regularly upgraded behind the scenes.
- Ensures developers always use the best coding-enhanced GPT-5 variant without changing model names.
7. Reliable Instruction Following
- Very strong adherence to constraints like:
- File/folder structure requirements
- Framework conventions
- Naming patterns
- Linting rules
- Makes it suitable for production coding agents.
8. Broad API Integration
- Available only in the Responses API, giving you:
- Streaming
- Structured outputs
- Function calling
- Allows creation of interactive coding tools and agent workflows with tight model control.
Use GPT-5.1 or GPT-5 Codex - or both
Appaca is the AI workspace for operators. Build internal tools and AI co-workers powered by GPT-5.1 or GPT-5 Codex - connected to your real data and ready for your whole team. No code, no deployment.
Describe it, and it's built
Tell the Appaca agent the internal tool you need and it builds a working app powered by GPT-5.1 or GPT-5 Codex. No code, no API keys, no deployment.
Switch models without rebuilding
Start on GPT-5.1, test the same tool on GPT-5 Codex, and keep whichever performs better - the rest of your app stays exactly as it is.
Automated for the whole team
Schedule tools to run on autopilot - daily digests, weekly reports, real-time triggers - and share them with your whole team from one workspace.
Describe it, and it's built
Tell the Appaca agent what your team needs and it builds a working app powered by GPT-5.1 or GPT-5 Codex - connected to the tools you already use.
Related comparisons
See how GPT-5.1 and GPT-5 Codex stack up against other models in the directory.
FAQs
They cost the same overall: both charge $1.25 per million input tokens and $10 per million output tokens.
They are equal: both GPT-5.1 and GPT-5 Codex support a 400K tokens context window.
It depends on the job. Compare the pricing, context window, and strengths above against your workload - and remember the choice isn't permanent. In Appaca you can build a tool on GPT-5.1, test the same tool on GPT-5 Codex, and switch at any time without rebuilding anything.
Yes. Appaca is a no-code AI workspace: describe the internal tool your team needs and the Appaca agent builds it as a working app powered by GPT-5.1, GPT-5 Codex, or any other model in the directory - with a built-in database, team access, and integrations. No API keys to wire up and nothing to deploy.
Build AI tools with GPT-5.1 or GPT-5 Codex
Describe the tool your team needs and get a working app powered by the model you choose - with a built-in database, team access, and integrations. No code, no deployment.