Claude Opus 5.5 vs GPT-6 Astra: API price, context and cost per task
Anthropic's and OpenAI's top models for agentic work, launched three weeks apart in September 2026. Opus 5.5 arrived with a price cut over Opus 5, while GPT-6 Astra kept the premium flagship rate.
On output, Claude Opus 5.5 is 2.5x cheaper ($20 vs $50 per million tokens). On input, Claude Opus 5.5 is 2.5x cheaper ($4 vs $10 per million tokens). GPT-6 Astra reads more per request: 1,050,000 tokens against 1,000,000.
Data updated 2026-11-11 - source: public OpenRouter model list, refreshed daily. Prices in USD, excluding VAT.
Specs and prices side by side
| Claude Opus 5.5 | GPT-6 Astra | |
|---|---|---|
| Vendor | Anthropic | OpenAI |
| Input, per 1M tokens | $4 | $10 |
| Output, per 1M tokens | $20 | $50 |
| Cached input, per 1M | $0.2 | $1 |
| Batch (input / output) | $2 / $10 | $5 / $25 |
| Context window | 1,000,000 | 1,050,000 |
| Max output | 128,000 | 128,000 |
| Input types | text, images, files | text, images, files |
| Reasoning | Yes | Yes |
| Tool calling | Yes | Yes |
| On OpenRouter since | 22 Sep 2026 | 4 Sep 2026 |
Highlighted: the cheaper price or the larger limit. "Not published" means the figure is not in the public model listing yet.
What a month of work costs
Four typical workloads at today's list prices. Reasoning models also bill their thinking as output tokens, so treat output-heavy numbers as a floor.
| Workload | Claude Opus 5.5 | GPT-6 Astra | Difference |
|---|---|---|---|
| Support chatbot10,000 conversations a month, about 1,500 input and 400 output tokens each | $140 | $350 | Claude Opus 5.5 2.5x cheaper |
| Coding agent300 tasks a month, about 80,000 input tokens (code context re-read across steps) and 8,000 output tokens each | $144 | $360 | Claude Opus 5.5 2.5x cheaper |
| Coding agent with caching70% of input served from the prompt cache | $80.16 | $209 | |
| Long-document analysis1,000 documents a month, about 50,000 tokens in and a 1,500-token summary out | $230 | $575 | Claude Opus 5.5 2.5x cheaper |
| Content drafting600 articles a month, about 3,000 tokens of brief in and 2,500 tokens of draft out | $37.20 | $93 | Claude Opus 5.5 2.5x cheaper |
Price stability over the last 30 days
- Claude Opus 5.5: no change in the last 30 days.
- GPT-6 Astra: no change in the last 30 days.
What the vendors and benchmarks say
Claude Opus 5.5
"Claude Opus 5.5 is Anthropic's flagship model for demanding reasoning, coding, and long-horizon agentic work, succeeding Claude Opus 5."model card on OpenRouter
- Released on 22 September 2026 as the first model of the Claude 5.5 family. Source: Anthropic
- Anthropic says a typical task at default settings costs 40% less than on Opus 5, because the model uses fewer tokens, and that generation is over 30% faster. Source: Anthropic
- Thinking is always on and cannot be switched off; the default effort level is medium (Opus 5 defaulted to high). Source: Anthropic model documentation
- Terminal-Bench 4.0: 66.4%; GDPval-AA v2.1: 1846 Elo. In Anthropic's test, 16 of 18 reports written from incomplete sources contained no invented figure. Source: Anthropic
- Fast mode costs $8 / $40 and batch mode $2 / $10 per million tokens; knowledge cutoff June 2026. Source: Anthropic
GPT-6 Astra
"GPT-6 Astra is OpenAI's flagship model for demanding end-to-end work."model card on OpenRouter
- OpenAI's flagship, presented on 3 September 2026 and rolled out in stages. Source: OpenAI
- Terminal-Bench 4.0: 57.9% (figure reported by OpenAI); GDPval-AA v2.1: 1542 Elo. Source: Anthropic's Claude Opus 5.5 launch comparison
Which one to pick
On Anthropic's numbers Opus 5.5 leads Astra on Terminal-Bench 4.0 (66.4% vs 57.9%) and on GDPval-AA v2.1 (1846 vs 1542), and it is also the cheaper of the two per token - so for coding agents and long knowledge-work tasks it is the one to test first. Astra makes sense if your stack is built on OpenAI tooling, you need its slightly larger window, or your own evals favour it. Vendor benchmarks are a starting point: run a week of your real tasks on both.
Cheaper models with a similar context window
Models from our comparison set that cost less than both on a blended basis and support tool calling. They are not equivalent in quality - test before switching.
- Kimi K3 (Moonshot AI): $0.192 / $16 per million tokens, 1.05M context
- GPT-6.1 Sol (OpenAI): $2 / $10 per million tokens, 1.05M context
- GPT-6 Sol (OpenAI): $2 / $10 per million tokens, 1.05M context
Related reading
- Claude Opus 5.5 vs GPT-6 Astra: Plan or API?
- Gemini 4 Argon Test: 23 Tasks vs Opus 5.5 and GPT-6 Astra
- Claude Fable 5.2 vs Opus 5.5: Price, Benchmarks, Which to Pick
- Claude Pro vs. Max vs. API: Opus 5.5 costs compared
- Claude Fable 5.2 vs GPT-6 Astra and Gemini 4 Carbon
- GPT-6.2 Astra: Leaks, Status and Rumours Before Launch
How we calculate
Prices are the public per-token list rates from OpenRouter's model list, which match the vendors' own API prices for first-party models and show the current routed price for open-weight models served by several hosts. Monthly costs multiply those rates by the token volumes in each workload; caching assumes the stated share of input is billed at the cached-input rate. Benchmarks and claims are quoted from the named sources, mostly the vendors themselves - treat them as a guide and test on your own tasks. See also the AI cost calculator and all tracked model prices.
Frequently asked questions
Which is cheaper, Claude Opus 5.5 or GPT-6 Astra?
As of 11 Nov 2026, Claude Opus 5.5 costs $4 per million input tokens and $20 per million output tokens; GPT-6 Astra costs $10 and $50. Claude Opus 5.5 is cheaper in 4 of the 4 monthly workloads we price on this page. The real bill also depends on how many reasoning tokens each model writes.
Which has the larger context window?
Claude Opus 5.5 reads up to 1,000,000 tokens and can write up to 128,000; GPT-6 Astra reads up to 1,050,000 and writes up to 128,000.
How much does a support chatbot cost on each model?
For 10,000 conversations a month (about 15 million input and 4 million output tokens) you would pay about $140 on Claude Opus 5.5 and $350 on GPT-6 Astra at list prices, before any caching or batch discounts.
Do they offer prompt caching or batch discounts?
Claude Opus 5.5 lists cached input at $0.2 per million and a batch rate of $2 / $10. GPT-6 Astra lists cached input at $1 per million and a batch rate of $5 / $25. Caching matters most for agents and chatbots that resend the same context on every turn.
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