API cost decision in 10 seconds

Claude Opus 4.5 vs GPT-5.1-Codex

Pick GPT-5.1-Codex when budget and context both matter.

Page updated:  Data confirmed:  Prices normalized to USD per 1M tokens Sample workload: 1M input + 500K output

Budget verdict

Pick GPT-5.1-Codex when budget and context both matter.

On the standard 1M input plus 500K output workload, GPT-5.1-Codex is estimated at $6.25 vs $17.5 for Claude Opus 4.5, saving $11.25 (64.3% lower).

Cost-first pickGPT-5.1-Codex
Context-first pickGPT-5.1-Codex
Sample savings$11.2564.3%
10x traffic gap$112.5

GPT-5.1-Codex is cheaper on the standard workload and also has the larger context window. At 10x that traffic, the same price gap is about $112.5. Use the calculator below to replace the sample workload with your own token volume.

Cost sensitivity

Workload Sensitivity

Same prices, different token mixes.

GPT-5.1-Codex stays cheaper across input-heavy, balanced, and output-heavy sample workloads.

Workload shapeToken mixBetter pickClaude Opus 4.5GPT-5.1-Codex
Input-heavy / RAG5M input + 500K outputGPT-5.1-Codex$37.5$11.25
Balanced workload1M input + 1M outputGPT-5.1-Codex$30$11.25
Output-heavy chatbot1M input + 5M outputGPT-5.1-Codex$130$51.25
Cheaper input GPT-5.1-Codex $5 vs $1.25 / 1M

GPT-5.1-Codex is $3.75 cheaper per 1M input tokens (75% lower; 4x difference).

Cheaper output GPT-5.1-Codex $25 vs $10 / 1M

GPT-5.1-Codex is $15 cheaper per 1M output tokens (60% lower; 2.5x difference).

Larger context GPT-5.1-Codex 200K vs 400K

GPT-5.1-Codex has 200K more context (2x larger).

Sample workload GPT-5.1-Codex $17.5 vs $6.25

GPT-5.1-Codex is $11.25 cheaper on the standard workload (64.3% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.
Claude Opus 4.5 Calculating… Estimated API cost
GPT-5.1-Codex Calculating… Estimated API cost
Cheaper for this workload Calculating… Difference: calculating…

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

Verdict

GPT-5.1-Codex has the lower input price; GPT-5.1-Codex has the lower output price; GPT-5.1-Codex offers the larger context window. For the 1M input plus 500K output sample, GPT-5.1-Codex is cheaper for the standard workload.

For a 1M input token plus 500K output token workload, the estimated API cost is $17.5 for Claude Opus 4.5 and $6.25 for GPT-5.1-Codex.

Best Fit

Choose Claude Opus 4.5 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 lower input-token price, lower output-token price, and larger context window.

Decision Notes
  • On the standard 1M input plus 500K output workload, GPT-5.1-Codex is estimated at $6.25 vs $17.5 for Claude Opus 4.5, saving $11.25 (64.3% lower).
  • GPT-5.1-Codex is $11.25 cheaper on the standard workload (64.3% lower).
  • GPT-5.1-Codex is $3.75 cheaper per 1M input tokens (75% lower; 4x difference).
  • GPT-5.1-Codex is $15 cheaper per 1M output tokens (60% lower; 2.5x difference).
  • GPT-5.1-Codex has 200K more context (2x larger).
Head-to-Head Specs
FeatureClaude Opus 4.5
(Anthropic)		GPT-5.1-Codex
(OpenAI)
Input Price
prompt tokens per 1M		$5$1.25
Completion Price
per 1M tokens		$25$10
Sample Workload Cost
1M input + 500K output		$17.5$6.25
Context Window200K400K
Release Date

Use-Case Decision Matrix

Use caseBetter pickWhy
Budget-constrained productionGPT-5.1-CodexOn the standard 1M input plus 500K output workload, GPT-5.1-Codex is estimated at $6.25 vs $17.5 for Claude Opus 4.5, saving $11.25 (64.3% lower).
High-volume input processingGPT-5.1-CodexLower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill.
Long responses and chatbotsGPT-5.1-CodexLower output-token price matters most when assistants generate many completion tokens.
RAG or long-document workGPT-5.1-CodexA larger context window leaves more room for retrieved passages, conversation history, or source files.

Related Alternatives

Same-provider lower-cost swaps
  • Claude 3 Haiku can replace Claude Opus 4.5 when lower sample workload cost matters most: $0.88.
  • Claude 3.5 Haiku can replace Claude Opus 4.5 when lower sample workload cost matters most: $2.8.
  • Anthropic Claude Haiku Latest can replace Claude Opus 4.5 when lower sample workload cost matters most: $3.5.
  • Claude Haiku 4.5 can replace Claude Opus 4.5 when lower sample workload cost matters most: $3.5.
Larger context near this budget
  • 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.
  • GPT-5.5 offers 1.05M context with $20 sample workload cost.

Cheaper alternatives

Review low-cost models sorted by a standard 1M input plus 500K output workload.

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Larger context alternatives

Find models with larger context windows for RAG, long documents, and codebase review.

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Provider catalogs

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Anthropic catalog

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OpenAI catalog

Check other OpenAI models with comparable pricing, context, or release timing.

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Claude Opus 4.5

Claude Opus 4.5 is Anthropic’s frontier reasoning model optimized for complex software engineering, agentic workflows, and long-horizon computer use. It offers strong multimodal capabilities, competitive performance across real-world coding and...

GPT-5.1-Codex

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....