API cost decision in 10 seconds

Claude Opus 5 (Fast) vs GPT-5.6 Terra Pro

Pick GPT-5.6 Terra Pro 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-5.6 Terra Pro when budget and context both matter.

On the standard 1M input plus 500K output workload, GPT-5.6 Terra Pro is estimated at $8 vs $35 for Claude Opus 5 (Fast), saving $27 (77.1% lower).

Cost-first pickGPT-5.6 Terra Pro
Context-first pickGPT-5.6 Terra Pro
Sample savings$2777.1%
10x traffic gap$270

GPT-5.6 Terra Pro is cheaper on the standard workload and also has the larger context window. At 10x that traffic, the same price gap is about $270. Use the calculator below to replace the sample workload with your own token volume.

Cost sensitivity

Workload Sensitivity

Same prices, different token mixes.

GPT-5.6 Terra Pro stays cheaper across input-heavy, balanced, and output-heavy sample workloads.

Workload shapeToken mixBetter pickClaude Opus 5 (Fast)GPT-5.6 Terra Pro
Input-heavy / RAG5M input + 500K outputGPT-5.6 Terra Pro$75$16
Balanced workload1M input + 1M outputGPT-5.6 Terra Pro$60$14
Output-heavy chatbot1M input + 5M outputGPT-5.6 Terra Pro$260$62
Cheaper input GPT-5.6 Terra Pro $10 vs $2 / 1M

GPT-5.6 Terra Pro is $8 cheaper per 1M input tokens (80% lower; 5x difference).

Cheaper output GPT-5.6 Terra Pro $50 vs $12 / 1M

GPT-5.6 Terra Pro is $38 cheaper per 1M output tokens (76% lower; 4.17x difference).

Larger context GPT-5.6 Terra Pro 1M vs 1.05M

GPT-5.6 Terra Pro has 50K more context (1.05x larger).

Sample workload GPT-5.6 Terra Pro $35 vs $8

GPT-5.6 Terra Pro is $27 cheaper on the standard workload (77.1% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.
Claude Opus 5 (Fast) Calculating… Estimated API cost
GPT-5.6 Terra Pro 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-5.6 Terra Pro has the lower input price; GPT-5.6 Terra Pro has the lower output price; GPT-5.6 Terra Pro offers the larger context window. For the 1M input plus 500K output sample, GPT-5.6 Terra Pro is cheaper for the standard workload.

For a 1M input token plus 500K output token workload, the estimated API cost is $35 for Claude Opus 5 (Fast) and $8 for GPT-5.6 Terra Pro.

Best Fit

Choose Claude Opus 5 (Fast) when its provider, model quality, latency, or availability is more important than the numeric price/context winner.

Choose GPT-5.6 Terra Pro 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-5.6 Terra Pro is estimated at $8 vs $35 for Claude Opus 5 (Fast), saving $27 (77.1% lower).
  • GPT-5.6 Terra Pro is $27 cheaper on the standard workload (77.1% lower).
  • GPT-5.6 Terra Pro is $8 cheaper per 1M input tokens (80% lower; 5x difference).
  • GPT-5.6 Terra Pro is $38 cheaper per 1M output tokens (76% lower; 4.17x difference).
  • GPT-5.6 Terra Pro has 50K more context (1.05x larger).
Head-to-Head Specs
FeatureClaude Opus 5 (Fast)
(Anthropic)		GPT-5.6 Terra Pro
(OpenAI)
Input Price
prompt tokens per 1M		$10$2
Completion Price
per 1M tokens		$50$12
Sample Workload Cost
1M input + 500K output		$35$8
Context Window1M1.05M
Release Date

Use-Case Decision Matrix

Use caseBetter pickWhy
Budget-constrained productionGPT-5.6 Terra ProOn the standard 1M input plus 500K output workload, GPT-5.6 Terra Pro is estimated at $8 vs $35 for Claude Opus 5 (Fast), saving $27 (77.1% lower).
High-volume input processingGPT-5.6 Terra ProLower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill.
Long responses and chatbotsGPT-5.6 Terra ProLower output-token price matters most when assistants generate many completion tokens.
RAG or long-document workGPT-5.6 Terra ProA 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 5 (Fast) when lower sample workload cost matters most: $0.88.
  • Claude Haiku 4.5 (batch) can replace Claude Opus 5 (Fast) when lower sample workload cost matters most: $1.75.
  • Claude 3.5 Haiku can replace Claude Opus 5 (Fast) when lower sample workload cost matters most: $2.8.
  • Claude Sonnet 5 (batch) can replace Claude Opus 5 (Fast) when lower sample workload cost matters most: $3.5.

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.

Open largest context models

Provider catalogs

Compare models within provider hubs before choosing a final API vendor.

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Anthropic catalog

Review all tracked Anthropic models before deciding whether this matchup is the right shortlist.

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OpenAI catalog

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

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Claude Opus 5 (Fast)

Fast-mode variant of [Opus 5](/anthropic/claude-opus-5) - identical capabilities with higher output speed at 2x pricing relative to regular Opus 5. Learn more in Anthropic's docs: https://platform.claude.com/docs/en/build-with-claude/fast-mode

GPT-5.6 Terra Pro

GPT-5.6 Terra Pro is the same underlying model as [GPT-5.6 Terra](https://openrouter.ai/openai/gpt-5.6-terra), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. Learn more in OpenAI's docs: https://developers.openai.com/api/docs/guides/reasoning#reasoning-mode