OpenAIGPT-5.5VSOpenAIGPT-5.6 Terra

Analysis by:the whichllmmodel Editorial Team|Updated: June 2026

Our Take

Both models perform almost identically, with an average score gap of just 2.7%. We recommend choosing GPT-5.6 Terra as it is the more cost-effective option (being 2.0x cheaper) without sacrificing any real-world capability.

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Model Specs

GPT-5.5

Website

Benchmarks & Scores

Coding (swe-bench-pro)

58.6%

excellent at multi-file repositories, autonomous agents, and industrial codebases

Reasoning (gpqa-diamond)Winner (+0.7%)

93.6%

graduate-level science QA

Cost & Context

Cost (per 1M tokens)

$11.25Input: $5.00 | Output: $30.00

Context Window

1.05M tokens

Model Specs

GPT-5.6 Terra

Website

Benchmarks & Scores

Coding (swe-bench-pro)Winner (+4.8%)

63.4%

excellent at multi-file repositories, autonomous agents, and industrial codebases

Reasoning (gpqa-diamond)

92.9%

graduate-level science QA

Cost & Context

Cost (per 1M tokens)2.0x cheaper

$5.63Input: $2.50 | Output: $15.00

Context Window

1.05M tokens

Read our data collection methodology

Frequently Asked Questions about GPT-5.5 vs GPT-5.6 Terra

GPT-5.6 Terra is cheaper than GPT-5.5. GPT-5.6 Terra has a blended cost of $5.63/1M tokens, which is about 2.0x cheaper than GPT-5.5 at $11.25/1M tokens.

GPT-5.6 Terra is better for coding tasks on this benchmark. It scores 63.4% on swe-bench-pro (excellent at multi-file repositories, autonomous agents, and industrial codebases) compared to GPT-5.5 which scores 58.6%.

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