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GPT-5.5 or GPT-6 Astra: which to choose?

GPT-5.5 (OpenAI) and GPT-6 Astra (OpenAI) compared point by point: measured performance, pricing, context and capabilities.

Data as of October 22, 2026

Side-by-side comparison

CriterionGPT-5.5GPT-6 Astra
DeveloperOpenAIOpenAI
ReleasedApril 23, 2026September 4, 2026
Capability index89 / 10094.7 / 100
Input price$5$10
Output price$30$50
Cost of a typical task$0.16$0.30
Context window1,050,000 tokens1,050,000 tokens
Maximum output128,000 tokens128,000 tokens
Reasoning modeYesYes
Tool callingYesYes
Accepted inputstext, image, PDFtext, image, PDF
Open weightsNoNo
Knowledge cutoffDecember 1, 2025April 30, 2026

The match-up at a glance

This comparison pits two frontier models, the ones you pick when quality comes first against each other: GPT-5.5 and GPT-6 Astra, both built by OpenAI. The first dates from April 23, 2026, the second from September 4, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

Which one is more capable?

On our capability index, GPT-5.5 scores 89 out of 100 and GPT-6 Astra 94.7. GPT-6 Astra leads by 5.7 points.

On the 5 benchmarks reported for both, GPT-5.5 wins 0 times and GPT-6 Astra 4:

  • GPQA Diamond (PhD-level science questions): GPT-5.5 94%, GPT-6 Astra 95.8%
  • OTIS Mock AIME (competition mathematics problems): GPT-5.5 100%, GPT-6 Astra 100%
  • FrontierMath (very hard research-level mathematics): GPT-5.5 85.3%, GPT-6 Astra 93.7%
  • FrontierCode (advanced programming tasks): GPT-5.5 43%, GPT-6 Astra 53.3%
  • APEX-Agents (professional tasks carried out by an agent): GPT-5.5 55.1%, GPT-6 Astra 64.7%

Budget

GPT-5.5 costs $5 per million input tokens and $30 per million output tokens; GPT-6 Astra costs $10 and $50.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.16 with GPT-5.5 versus $0.30 with GPT-6 Astra. GPT-5.5 is 1.9 times cheaper, a gap that adds up quickly over 1,000 tasks: $140 difference.

Run the numbers with your own volumes in the agent cost calculator.

Context and capabilities

Both models have the same context window: 1,050,000 tokens, roughly 1,575 pages.

Reasoning mode: GPT-5.5 yes, GPT-6 Astra yes. Tool calling: GPT-5.5 yes, GPT-6 Astra yes. Image input: GPT-5.5 yes, GPT-6 Astra yes.

Neither publishes its weights: both are used through an API.

Knowledge cutoff: December 1, 2025 for GPT-5.5, April 30, 2026 for GPT-6 Astra.

In short

Our reading of the data:

  • Choose GPT-5.5 for a lower cost.
  • Choose GPT-6 Astra for a higher capability index and a more recent release.

This verdict relies on public figures; it does not replace a trial on your own tasks.

Other comparisons

Frequently asked questions

GPT-5.5 or GPT-6 Astra: which is better?

On our index (Epoch AI data), GPT-5.5 scores 89 and GPT-6 Astra 94.7 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

GPT-5.5. To read 20,000 tokens and write 2,000, expect $0.16 with GPT-5.5 and $0.30 with GPT-6 Astra (prices as of October 22, 2026).

Which one has the larger context window?

Neither: both accept 1,050,000 tokens.

Can I run GPT-5.5 or GPT-6 Astra on my own servers?

No: both are closed models, available through an API.

Data sources

Data as of October 22, 2026

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