By the toolist.ai editors. Researched from public sources, not hands-on tested by toolist.ai. Updated October 6, 2026; prices checked October 6, 2026.

Claude Opus 5.5 vs GPT-6 Astra

Verdict

Claude Opus 5.5 is the better buy for almost everyone. It costs 60% less per token ($4 and $20 against $10 and $50) and beats GPT-6 Astra on seven of the eight benchmarks both have. Astra keeps a lead on Terminal-Bench-Science and returns its first token faster at medium effort.

Verdict based on published prices, limits and benchmarks, not on our own tests.

Choose Claude Opus 5.5 if

  • You want the higher score for less money: 57.6 against 52.7 on the Intelligence Index at 40% of the token price
  • Your work is knowledge work or research (1866 against 1542 Elo on GDPval-AA; 61.4% against 54.7% on Humanity's Last Exam)
  • Your prompts run past 272,000 tokens, where Anthropic adds no surcharge and OpenAI doubles Astra's input price

Choose GPT-6 Astra if

  • Your work is scientific terminal work (63.3% against 59.0% on Terminal-Bench-Science)
  • You want a fast first token: 5.5 seconds for Astra against 20.6 for Opus 5.5, both at medium effort
  • You need OpenAI's Ultrafast mode for lower latency, at six times the standard price

Price

Input costs 2.5 times as much on GPT-6 Astra as on Claude Opus 5.5. Output costs 2.5 times as much on GPT-6 Astra as on Claude Opus 5.5.

Per million tokensClaude Opus 5.5GPT-6 Astra
Input$4 source$10 source
Cached input$0.20 source$1 source
Output$20 source$50 source

Claude Opus 5.5: Cache writes cost $5 per million tokens (5-minute cache) or $8 (1-hour cache). The Batch API costs half. There is no long-context surcharge. Fast mode costs $8 in and $40 out.

GPT-6 Astra: Prompts over 272,000 input tokens are billed at twice the input rate and 1.5 times the output rate for the whole request. Batch and Flex cost half; Fast mode costs double and Ultrafast six times.

Worked example: what a month costs

We priced three monthly workloads at the standard rates. The provider does not publish these figures.

WorkloadClaude Opus 5.5GPT-6 Astra
Support chatbot
100,000 replies, each 3,000 input and 400 output tokens, no caching (300M in, 40M out)		 $2,000$5,000
Document Q&A
5,000 questions over the same 60,000-token document set (90% cache hits), 800 output tokens each (300M in, 4M out)		 $254$770
Coding agent
200 tasks, each 1.5 million input tokens (90% cache hits) and 50,000 output tokens (300M in, 10M out)		 $374$1,070

Price your own workload

ModelCost a month
Claude Opus 5.5 $300
GPT-6 Astra $750

Standard API prices, no batch or priority discounts. Cached input is billed at the cache-read price; cache-write charges are not included. Reasoning models bill their thinking as output tokens.

Limits and release dates

Claude Opus 5.5GPT-6 Astra
ReleasedSeptember 22, 2026 sourceSeptember 3, 2026 source
Context window1,000,000 tokens source1,050,000 tokens source
Maximum output128,000 tokens source128,000 tokens source
Knowledge cutoffJune 2026 sourceApril 30, 2026 source
Input and outputText and images in; text out sourceText and images in; text out source
API model nameclaude-opus-5-5gpt-6-astra

Benchmarks

Scores as published by the provider or measured by Artificial Analysis; higher is better. A dash means no score was published.

BenchmarkClaude Opus 5.5GPT-6 Astra
Artificial Analysis Intelligence Index
max effort		 57.6 source52.7 source
Intelligence Index at everyday effort 51.2 (medium effort, the API default) source49.6 (medium effort; OpenAI publishes no default) source
Coding Agent Index 66.0 (Claude Code harness, max effort) source61.6 (Codex harness, max effort) source
Terminal-Bench 4.0
max effort		 59.6% source59.1% source
Humanity's Last Exam
max effort		 61.4% source54.7% source
GDPval-AA v2.1 (Elo)
max effort		 1866 source1542 source
SciCode
max effort		 66.9% source56.5% source
Terminal-Bench-Science 0.1
max effort		 59.0% source63.3% source
GPQA Diamond –96.1% (max effort) source
Output speed 79.2 tokens/s (medium effort, Anthropic API) source50.9 tokens/s (medium effort, OpenAI API) source

Benchmark and speed data from Artificial Analysis where linked.

Read more

Sources