How is GPT-6 Astra different from GPT-5.6 Sol?

Astra is the September 2026 top tier of GPT-6; 5.6 Sol is the July flagship of GPT-5.6. Both have a 1.05M context window and 128K output. The differences: Astra rejects reasoning_effort: none while 5.6 Sol accepts it; Astra's knowledge cutoff is April 30, 2026 against 5.6 Sol's February 16; and OpenAI says Astra stays more coherent over long tasks.

When is GPT-6.1 Sol enough?

OpenAI says 6.1 Sol comes close to Astra on complex coding, computer use and professional work, and recommends comparing the two on your own tasks. They share the context window, output limit and reasoning effort values, so switching is a change to the model field and you can run the same batch on each before deciding.

What changes when moving from GPT-5.6 to Astra?

Following OpenAI's migration guide: replace reasoning_effort: none with low, and when effort is not none, drop temperature, top_p and top_logprobs, plus logprobs in Chat Completions. The rest of the request shape stays the same.

Does the price change above 272K input tokens?

Yes. A request whose input exceeds 272K tokens is billed entirely at the long-context rate, not just the part above the threshold. The pricing section above lists both tiers.

GPT-6 Astra

Save 85%Official

openai/gpt-6-astra

Also callable as gpt-6

Released by OpenAI on September 3, 2026 — the top of the GPT-6 line.

Get an API key View code sample

Live model playground

Try GPT-6 Astra here

Tune the request, see the current price ceiling, and inspect the real response without leaving this model page.

streamchat

1Configure input

Prompt

230 / 20,000

Add images

Maximum estimated cost—

2Live resultExample

GPT-6 Astra

async function load(id) { try { const r = await fetch('/api/items/' + id); const data = await r.json(); return data.name; } catch { return null; } }

Context window: 1.05M
Max output: 128K
Input modalities: TextImage
Output modalities: Text
Capabilities: Vision · Reasoning · Tool calling · Coding · Prompt cache · Paid cache writes
Upstream release: 2026-09-03
RouteMux name: openai/gpt-6-astra

What is GPT-6 Astra

GPT-6 Astra was released by OpenAI on September 3, 2026, as the top tier of the GPT-6 family and the successor to the GPT-5.6 flagship. OpenAI's changelog says it is built for the hardest end-to-end work, and the model page recommends it for complex reasoning, coding, computer use, research and document creation. OpenAI also reports that in several evaluations Astra achieved stronger results using substantially fewer output tokens.

The specs: a 1.05M-token context window (up to 922K input), 128K max output, text and image in, text out, and a knowledge cutoff of April 30, 2026. Reasoning effort takes low, medium, high, xhigh or max, with medium as the default; none is not accepted, so reasoning cannot be switched off entirely. On RouteMux it supports tool calling and explicit prompt caching, and it is reachable over OpenAI Chat Completions, OpenAI Responses and Anthropic Messages, so an Anthropic-shaped client can call it without rewriting its request layer.

Compared with the previous flagship, GPT-5.6 Sol, OpenAI says Astra is generally better at staying coherent over long tasks and more likely to ask for clarification where earlier models would make assumptions. Within GPT-6, OpenAI describes GPT-6.1 Sol, released September 29, as near-Astra and suggests testing both on your tasks. Stay on GPT-5.6 Sol when requests need reasoning_effort: none, or when you rely on the 5.6 family's default cross-turn reasoning and reasoning reuse across its three tiers.

At the standard tier (input up to 272K tokens) it bills $1.5 per 1M input tokens and $7.5 per 1M output tokens, with cached input at $0.15 per 1M tokens. OpenAI lists $10, $50 and $1 for the same three.

Before you choose

How is GPT-6 Astra different from GPT-5.6 Sol?: Astra is the September 2026 top tier of GPT-6; 5.6 Sol is the July flagship of GPT-5.6. Both have a 1.05M context window and 128K output. The differences: Astra rejects reasoning_effort: none while 5.6 Sol accepts it; Astra's knowledge cutoff is April 30, 2026 against 5.6 Sol's February 16; and OpenAI says Astra stays more coherent over long tasks.
When is GPT-6.1 Sol enough?: OpenAI says 6.1 Sol comes close to Astra on complex coding, computer use and professional work, and recommends comparing the two on your own tasks. They share the context window, output limit and reasoning effort values, so switching is a change to the model field and you can run the same batch on each before deciding.
What changes when moving from GPT-5.6 to Astra?: Following OpenAI's migration guide: replace reasoning_effort: none with low, and when effort is not none, drop temperature, top_p and top_logprobs, plus logprobs in Chat Completions. The rest of the request shape stays the same.
Does the price change above 272K input tokens?: Yes. A request whose input exceeds 272K tokens is billed entirely at the long-context rate, not just the part above the threshold. The pricing section above lists both tiers.

GPT-6 Astra API pricing

Prices verified 2026-10-18

InputOfficial $10 / M tokens

$1.5/ M tokensSave 85%

OutputOfficial $50 / M tokens

$7.5/ M tokensSave 85%

Fast $3 / $15 /M

Cache read $0.15/M · Cache write $1.875/M

Tier	Input	Cache read	Cache write	Output
Standard ≤272K	$1.5~~$10~~−85%	$0.15$1−85%	$1.875~~$12.5~~−85%	$7.5~~$50~~−85%
Standard >272K	$3~~$20~~−85%	$0.3$2−85%	$3.75~~$25~~−85%	$11.25~~$75~~−85%
Priority ≤272K	$3~~$20~~−85%	$0.3$2−85%	$3.75~~$25~~−85%	$15~~$100~~−85%
Priority >272K	$6~~$40~~−85%	$0.6$4−85%	$7.5~~$50~~−85%	$22.5~~$150~~−85%

Estimate cost

Input tokensOutput tokens

Estimated cost$0.0225

Key capabilities

Top of the GPT-6 family: OpenAI built it for the hardest end-to-end work and recommends it for complex reasoning, coding, computer use, research and document creation.
More coherent on long tasks: OpenAI says Astra is generally better than GPT-5.6 Sol and earlier models at staying coherent during long tasks.
Reasoning from low to max: reasoning_effort takes low, medium, high, xhigh or max, defaulting to medium; none is rejected.
1.05M-token context: Up to 922K input tokens and 128K output tokens, with a knowledge cutoff of April 30, 2026.

Limited time10% extra Credits on your first top-up — up to 200 bonus Credits

Applies to your first top-up within 72 hours of signing up. Minimum $20, once per account.

Interface and protocols

OpenAI Chat CompletionsStreamingOpenAI ResponsesStreamingAnthropic MessagesStreaming

Use any of these IDs to call this model via the API.

RouteMux nameopenai/gpt-6-astra

Common namegpt-6

Replace the ROUTEMUX_KEY placeholder with your API key. Create one →

from openai import OpenAI

client = OpenAI(
    base_url="https://api.routemux.com/v1",
    api_key="<ROUTEMUX_KEY>",
)

completion = client.chat.completions.create(
    model="openai/gpt-6-astra",
    messages=[{"role": "user", "content": "What is the meaning of life?"}],
)
print(completion.choices[0].message.content)

base_url: https://api.routemux.com/v1

Performance (last 30 days)

15,199 requests · last 30 days

Total usage1386.76M

P50 first-token latency4.81s

Avg throughput16 tok/s

Success rate100.0%

Uptime · 24htested via openai_chat

100.00%

Success rate · 60d · from real requests

GPT-6 Astra FAQ

›What is GPT-6 Astra?

Released by OpenAI on September 3, 2026 — the top of the GPT-6 line.

›How large is the context window of GPT-6 Astra?

GPT-6 Astra supports a context window of up to 1.05M tokens, with up to 128K output tokens per request.

›How much does the GPT-6 Astra API cost?

Through RouteMux, GPT-6 Astra costs $1.5 for input and $7.5 for output (USD per 1M tokens), below the official list price.

›How do I call GPT-6 Astra via API?

GPT-6 Astra is OpenAI-compatible: point your base URL at RouteMux and set the model field to openai/gpt-6-astra — no code changes needed.

›Which input and output modalities does GPT-6 Astra support?

GPT-6 Astra accepts text, image as input and produces text as output.

›When was GPT-6 Astra released?

GPT-6 Astra was released on September 3, 2026.

Sources

Reviewed by the RouteMux team on 2026-10-24

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