Both models report the same input price at $1.25 per 1M tokens.
API cost decision in 10 seconds
GPT-5.1 Chat vs GPT-5.1-Codex
The standard workload cost is tied; choose by context window, provider fit, latency, or model quality.
Pricing data updated:
Prices normalized to USD per 1M tokens
Sample workload: 1M input + 500K output
Budget verdict
The standard workload cost is tied; choose by context window, provider fit, latency, or model quality.
Both models are estimated at $6.25 for the standard 1M input plus 500K output workload.
Cost-first pickTie
Context-first pickGPT-5.1-Codex
Sample savings$00%
10x traffic gap$0
Context-window winner: GPT-5.1-Codex. Cost does not separate this pair on the standard workload, so the next decision point is context window and model behavior.
Cost sensitivity
Workload Sensitivity
The two models stay tied across the input-heavy, balanced, and output-heavy sample workloads.
| Workload shape | Token mix | Better pick | GPT-5.1 Chat | GPT-5.1-Codex |
|---|---|---|---|---|
| Input-heavy / RAG | 5M input + 500K output | Tie | $11.25 | $11.25 |
| Balanced workload | 1M input + 1M output | Tie | $11.25 | $11.25 |
| Output-heavy chatbot | 1M input + 5M output | Tie | $51.25 | $51.25 |
Both models report the same output price at $10 per 1M tokens.
GPT-5.1-Codex has 272K more context (3.12x larger).
Both models have the same estimated cost for the standard 1M input plus 500K output workload: $6.25.
Estimate your workload cost
Your Workload Cost
This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.
Quick Decision
both models tie on input price; both models tie on output price; GPT-5.1-Codex offers the larger context window. For the 1M input plus 500K output sample, the standard workload cost is tied.
For a 1M input token plus 500K output token workload, the estimated API cost is $6.25 for GPT-5.1 Chat and $6.25 for GPT-5.1-Codex.
Choose GPT-5.1 Chat when its provider, model quality, latency, or availability is more important than the numeric price/context winner.
Choose GPT-5.1-Codex when you care most about larger context window.
- Both models are estimated at $6.25 for the standard 1M input plus 500K output workload.
- Both models have the same estimated cost for the standard 1M input plus 500K output workload: $6.25.
- Both models report the same input price at $1.25 per 1M tokens.
- Both models report the same output price at $10 per 1M tokens.
- GPT-5.1-Codex has 272K more context (3.12x larger).
| Feature | GPT-5.1 Chat (OpenAI) | GPT-5.1-Codex (OpenAI) |
|---|---|---|
| Input Price prompt tokens per 1M | $1.25 | $1.25 |
| Completion Price per 1M tokens | $10 | $10 |
| Sample Workload Cost 1M input + 500K output | $6.25 | $6.25 |
| Context Window | 128K | 400K |
| Release Date |
Use-Case Decision Matrix
| Use case | Better pick | Why |
|---|---|---|
| Budget-constrained production | Tie | Both models are estimated at $6.25 for the standard 1M input plus 500K output workload. |
| High-volume input processing | Tie | Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill. |
| Long responses and chatbots | Tie | Lower output-token price matters most when assistants generate many completion tokens. |
| RAG or long-document work | GPT-5.1-Codex | A larger context window leaves more room for retrieved passages, conversation history, or source files. |
Related Alternatives
- gpt-oss-120b (free) can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.
- gpt-oss-20b (free) can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.
- gpt-oss-20b can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.1.
- gpt-oss-120b can replace GPT-5.1 Chat when lower sample workload cost matters most: $0.13.
- Llama 4 Scout offers 10M context with $0.23 sample workload cost.
- Grok 4.20 Multi-Agent offers 2M context with $5 sample workload cost.
- Grok 4.20 offers 2M context with $2.5 sample workload cost.
- Owl Alpha offers 1.05M context with $0 sample workload cost.
- No popular competitor is currently available.
Cheaper alternatives
Review low-cost models sorted by a standard 1M input plus 500K output workload.
Open cheapest modelsLarger context alternatives
Find models with larger context windows for RAG, long documents, and codebase review.
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Open provider hubsOpenAI catalog
Review all tracked OpenAI models before deciding whether this matchup is the right shortlist.
Open OpenAI modelsGPT-5.1 Chat (AKA Instant is the fast, lightweight member of the 5.1 family, optimized for low-latency chat while retaining strong general intelligence. It uses adaptive reasoning to selectively “think” on...
GPT-5.1-Codex is a specialized version of GPT-5.1 optimized for software engineering and coding workflows. It is designed for both interactive development sessions and long, independent execution of complex engineering tasks....