GPT vs Claude vs Gemini 2026: GPT-6 Astra vs Claude Fable 5.1

Short answer: for the hardest coding, agent, and knowledge work, two new flagships compete in the same price band — Claude Fable 5.1 and GPT-6 Astra (both $15 per 1M input tokens and $75 per 1M output tokens on Onysoft). Claude Sonnet 5 and Opus 5 lead for everyday coding and deep analysis, GPT-5.6 for writing and general-purpose production, and the Gemini Flash class (including the new 3.8 Flash) for speed and high-volume workloads.

Most "GPT vs Claude vs Gemini" comparisons online pit the ChatGPT, Claude, and Gemini chat subscriptions against each other and wave at the API side in two sentences. This guide does the opposite: we compare the three families from a developer's perspective, task by task — coding, agent tasks, writing, analysis, speed, cost, vision. And instead of recycled benchmark chatter, the evidence is verifiable: live Onysoft sale prices measured on September 13, 2026 (with Turkish lira equivalents), plus the positioning and benchmark claims the providers themselves published — with each claim clearly attributed.

The goal is not to crown a winner; all three families are production-grade, and the right question is not "which is best" but "which is best for this task". Our deep dives on September 2026's new models are live too: GPT-6 Astra, Claude Fable 5.1, and Gemini 3.8 Flash. For a family-by-family overview, see our AI model families guide; this article focuses on the head-to-head comparison and the decision matrix.

Which Model for Which Task? The Decision Matrix

The task-level summary: Claude Fable 5.1 and GPT-6 Astra for the hardest coding and agent work, Claude for everyday code and analysis, GPT-5.6 for writing, Gemini Flash for speed and volume. The matrix below shows our first pick and the strong alternative across seven task axes:

Task	First pick	Strong alternative	Why
Code generation and refactoring	Claude Sonnet 5 (everyday) / Claude Fable 5.1 (hardest jobs)	GPT-6 Astra	Anthropic positions Fable 5.1 among "the world's most advanced models" for coding and knowledge work; Sonnet 5 carries the everyday load in the same family at one fifth of the price ($3 / $15)
Long, multi-step agent tasks	GPT-6 Astra	Claude Fable 5.1	OpenAI positions Astra for computer and browser use, writing and running code, and long tasks with less human steering; both models share the same price ($15 / $75)
Content and writing	GPT-5.6 Sol / Terra	Claude Sonnet 5	GPT-5.6 Sol and Sonnet 5 cost exactly the same ($3 / $15); run the same prompt through both to settle tone and format
Long documents and analysis	Claude Opus 5 (1M context)	Gemini 3.1 Pro	Deep reasoning over wide context; Opus 5 costs half as much as Fable 5.1 ($7.50 / $37.50)
Real-time / low latency	Gemini Flash class (3.8 / 3.7 / 3.6 Flash)	GPT-5.6 Luna	The Flash class is built for the speed/cost equation; 3.8 Flash spends more thinking tokens, so compare it with earlier Flash releases when latency is critical
Cost-sensitive high volume	GPT-5.6 Luna / Gemini 3.1 Flash Lite	DeepSeek V4 Flash / V4.1 Flash	$0.30 (Luna) and $0.375 (3.1 Flash Lite) per 1M input tokens; DeepSeek V4 Flash at $0.0735 / $0.147 is the cheapest option in this article
Vision and multimodal input	Gemini 3.8 Flash	Qwen3.8 Max 0902	According to Google, 3.8 Flash accepts text, image, audio, video, and PDF input; Qwen3.8 Max takes text, image, and video input

The matrix assumes quality-first. When budget takes priority, stepping one tier down within the same family (Opus or Sonnet instead of Fable, GPT-5.6 instead of Astra) is enough for most production pipelines. For teams willing to look beyond the big three, the DeepSeek, Kimi, Qwen, and Grok notes are below.

How Do the Three Split on Coding, Writing, and Analysis?

The clearest split: on the hardest coding and agent work, the new flagships Claude Fable 5.1 and GPT-6 Astra sit in the same price band; Claude Sonnet 5 and Opus 5 lead on everyday code and deep analysis, GPT-5.6 on fluent writing, while Gemini positions itself on multimodal input and volume work.

On code, the Claude family plays three tiers. Claude Fable 5.1 (September 1, 2026) is the top of the family: according to Anthropic, it matches or beats Fable 5 at low and medium effort, performs much higher at high effort, and cuts cybersecurity false positives in Claude Code by roughly 60%; its Terminal-Bench-Science score as reported in the press is 52.6% (MarkTechPost). Claude Opus 5, with its 1M-token context, can take large codebases in a single request — a strong option for complex refactors and architecture reviews. Claude Sonnet 5, at $3 input / $15 output per 1M tokens (against Opus 5 at $7.50 / $37.50 and Fable 5.1 at $15 / $75), is the workhorse for day-to-day coding loads. Anthropic's own coding tool, Claude Code, is built on this family. Note: Onysoft is a member of the Anthropic Claude Partner Network; we provide Claude access under that official partnership. Deep dive: the Claude Fable 5.1 API guide.

On the GPT side, the new flagship is GPT-6 Astra (September 3, 2026). OpenAI positions it as "the world's smartest and most aligned model", highlighting software engineering, computer/browser use, professional work, and science. According to the provider, Astra can work across file collections, write and run code, and carry long tasks with less steering. OpenAI also states that Astra is the first model to meet the "Critical" cybersecurity threshold in its Preparedness Framework and that cyber-sensitive capabilities sit behind a trusted-access program. On Onysoft, openai/gpt-6-astra and its pro reasoning mode openai/gpt-6-astra-pro share the same price ($15 / $75); details in the GPT-6 Astra API guide.

On writing and content, the previous-generation GPT-5.6 family is still a safe harbor: Sol ($3 / $15) and Terra ($3 / $18) for everyday content production, and Luna ($0.30 / $1.80) as the light, fast end. Because Sol costs exactly the same as Claude Sonnet 5, the writing decision comes down to output preference rather than price — send the same prompt to both and decide.

Long-document analysis is Claude Opus 5 territory; Gemini 3.1 Pro ($3 / $18) is the alternative with wide context and multimodal capability. On vision input, the new Gemini 3.8 Flash accepts text, image, audio, video, and PDF according to Google; Gemini carries the strongest multimodal emphasis of the three. Image generation, however, is not this trio's job — that belongs to the dedicated image models in the catalog (for example Nano Banana 2).

Where Do Speed and Cost Land? (With DeepSeek, Kimi, Qwen, and Grok Notes)

On speed, the Gemini Flash class and GPT-5.6 Luna lead; on cost, DeepSeek leads; and beyond the trio, Kimi K3, Qwen3.8 Max, and Grok 4.6 are strong alternatives.

Speed: For real-time assistants, live chat, and streaming scenarios, Flash-class models and GPT-5.6 Luna are built for low latency. A caveat for the new Gemini 3.8 Flash: according to Google, the model deliberately spends more thinking tokens, which can mean longer response times and more output tokens for the same job. Since 3.7 Flash and 3.6 Flash are in the catalog at the same price ($1.125 / $5.625), comparing all three on your own prompts is the right move when latency is critical. The new models have only been in the catalog for a few days, so there is no meaningful platform latency measurement yet — which is why we give no latency figures here.

Cost: Among the GPT, Claude, and Gemini models in the table below, the cheapest is GPT-5.6 Luna ($0.30 input / $1.80 output per 1M tokens), followed by Gemini 3.1 Flash Lite ($0.375 / $2.25). Step outside the trio and DeepSeek V4 Flash asks $0.0735 input / $0.147 output — clearly cheaper than Luna on both sides. DeepSeek V4.1 Flash ($0.225 / $0.90), generally available since September 10, adds native image understanding and MIT-licensed weights, and one tier up sits DeepSeek V4 Pro ($2.40 / $4.80). There is a saving on the flagship side too: openai/gpt-6-astra:batch, a separate model ID for non-urgent GPT-6 Astra work, is offered at half price ($7.50 / $37.50).

Beyond the trio: If you need agent automation plus long context, Kimi K3 with its 1M-token context ($3.97 / $19.92) is a candidate worth testing — details in our Kimi K3 API guide. Qwen3.8 Max 0902 ($3 / $9, 1M context, text+image+video input) and xAI's Grok 4.6 ($3 / $9, 500K context) come in far below the flagships on output price, and if you need 2M tokens of context, Grok 4.20 ($1.875 / $3.75) is the model to look at. With 750+ models reachable through the same key, "one of the big three" is never an obligation.

GPT vs Claude vs Gemini API Pricing: The Live Table (with TRY Equivalents)

The pricing comparison speaks plainly: within a family, tiers differ by up to 50x (GPT-6 Astra at $15 input versus GPT-5.6 Luna at $0.30); across families, the flagships price very close to each other — in fact identically. The table below shows current sale prices on Onysoft (per 1M tokens):

Model	Input ($/1M)	Output ($/1M)	Input (TRY/1M)	Output (TRY/1M)	Context
openai/gpt-6-astra	$15.00	$75.00	727.41 TL	3,637.06 TL	1,050,000
openai/gpt-6-astra:batch	$7.50	$37.50	363.71 TL	1,818.53 TL	—
openai/gpt-5.6-sol	$3.00	$15.00	145.48 TL	727.41 TL	1,050,000
openai/gpt-5.6-terra	$3.00	$18.00	145.48 TL	872.89 TL	1,050,000
openai/gpt-5.6-luna	$0.30	$1.80	14.55 TL	87.29 TL	1,050,000
anthropic/claude-fable-5.1	$15.00	$75.00	727.41 TL	3,637.06 TL	1,000,000
anthropic/claude-opus-5	$7.50	$37.50	363.71 TL	1,818.53 TL	1,000,000
anthropic/claude-sonnet-5	$3.00	$15.00	145.48 TL	727.41 TL	1,000,000
anthropic/claude-haiku-4.5	$1.50	$7.50	72.74 TL	363.71 TL	200,000
google/gemini-3.8-flash	$1.125	$5.625	54.56 TL	272.78 TL	1,048,576
google/gemini-3.1-pro-preview	$3.00	$18.00	145.48 TL	872.89 TL	1,048,576
google/gemini-3.1-flash-lite	$0.375	$2.25	18.19 TL	109.11 TL	1,048,576
deepseek/deepseek-v4.1-flash	$0.225	$0.90	10.91 TL	43.64 TL	1,048,576
deepseek/deepseek-v4-flash	$0.0735	$0.147	3.56 TL	7.13 TL	1,048,576
deepseek/deepseek-v4-pro	$2.40	$4.80	116.39 TL	232.77 TL	1,048,576
moonshotai/kimi-k3	$3.97	$19.92	192.63 TL	966.20 TL	1,048,576

Prices are Onysoft sale prices as of September 13, 2026; see /models for current pricing. TRY equivalents are calculated at the September 11, 2026 TCMB rate (1 USD = 48.4941 TRY).

Four practical takeaways: (1) In the flagship class, GPT-6 Astra and Claude Fable 5.1 cost exactly the same ($15 / $75), while Claude Opus 5 sits at half that ($7.50 / $37.50) — the same level as Astra's batch ID. (2) In the mid-tier, GPT-5.6 Sol and Claude Sonnet 5 share one price ($3 / $15), and GPT-5.6 Terra and Gemini 3.1 Pro share another ($3 / $18); Gemini 3.8 Flash costs less than half of that level. (3) The bulk of any invoice almost always comes from output tokens — compare the output column first. (4) Onysoft bills every request on the model's input and output token counts times the sale price; special pricing mechanics on providers' own direct APIs — for example the cache-read discount Anthropic announced with Fable 5.1 — are not reflected in this table. To run the numbers on your own volume, the cost calculator is ready, and our AI API pricing guide covers every family.

The September 2026 Wave: What Providers Announced, and What Is on Onysoft

In the August version of this article, this section held our platform's 30-day usage table. We removed it in the September update: the new flagships have only been in the catalog for a few days, and their usage data is not yet enough for a meaningful comparison — setting the old distribution next to the new models would mislead. Instead, here is what changed in and around the three families over the last two weeks, with every claim attributed:

Model	Announced	What the provider highlights	On Onysoft
Claude Fable 5.1	Anthropic, September 1, 2026	Coding and knowledge work; a clear gain over Fable 5 at high effort; discovers vulnerabilities, does not develop exploits	Active: anthropic/claude-fable-5.1, ~anthropic/claude-fable-latest
Gemini 3.8 Flash	Google, September 2, 2026	Third Flash in six weeks; built on 3.7 Flash, spends more thinking tokens; text/image/audio/video/PDF input	Active: google/gemini-3.8-flash
GPT-6 Astra	OpenAI, September 3, 2026	Computer/browser use, software engineering, professional work, and science; phased rollout	Active: openai/gpt-6-astra, openai/gpt-6-astra-pro, openai/gpt-6-astra:batch, ~openai/gpt-astra-latest
DeepSeek V4.1 Flash	DeepSeek, September 10, 2026 (general availability)	552B-parameter multimodal MoE, CED architecture, native image understanding, MIT-licensed weights	Active: deepseek/deepseek-v4.1-flash
Qwen3.8 Max 0902	Qwen, early September	Quiet update (0902 snapshot); 2.4T-parameter MoE; text, image, and video input	Active: qwen/qwen3.8-max-0902

An honesty note: some models announced in the same wave are not in the Onysoft catalog. Claude Mythos 5.1, which Anthropic offers by invitation alongside Fable 5.1, Google's restricted Gemini 3.8 Flash Cyber, and Grok 4.7, which xAI announced on September 12, are currently unavailable; none of the recommendations in this article rely on them. For the full wave, see our September 2026 new AI models roundup. The positioning and benchmark statements in the table are claims by the providers or the press; the fastest way to verify them on your own workload is to run the same prompt across models side by side in the Playground.

How It Works on Onysoft: All Three Families Behind One API

The practical conclusion of this comparison: the right architecture is not picking one model, it is routing each task to the right model — and that does not require three accounts and three invoices. On Onysoft AI Gateway you create a free account, generate an sk-ony- prefixed key from the dashboard, and add balance in Turkish lira (converted at the TCMB rate, pay as you go, no subscription). One OpenAI-compatible endpoint reaches 750+ models with the same key; switching families is nothing more than changing the model parameter:

curl https://api.onysoft.com/v1/chat/completions \
  -H "Authorization: Bearer sk-ony-YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-sonnet-5",
    "messages": [{"role": "user", "content": "Review this function and suggest a refactor."}]
  }'

With streaming off, the response body comes inside a success/data envelope; if you work with raw HTTP, read the content from data.choices[0].message.content. That is why the smoothest path with the OpenAI Python SDK is to send requests with streaming on: streamed chunks arrive in raw OpenAI format, and the SDK reads them directly. Setting up task-based routing in code takes a few lines — one client, model chosen by task type, response pieces joined together:

from openai import OpenAI

client = OpenAI(
    base_url="https://api.onysoft.com/v1",
    api_key="sk-ony-YOUR_KEY",
)

TASK_MODEL = {
    "hard_code": "anthropic/claude-fable-5.1",   # hardest coding and knowledge work
    "code":      "anthropic/claude-sonnet-5",    # everyday coding and analysis
    "agent":     "openai/gpt-6-astra",           # long, multi-step tasks
    "writing":   "openai/gpt-5.6-sol",           # content production
    "volume":    "google/gemini-3.8-flash",      # classification, summaries
}

def ask(task, message):
    stream = client.chat.completions.create(
        model=TASK_MODEL[task],
        messages=[{"role": "user", "content": message}],
        stream=True,
    )
    parts = []
    for chunk in stream:
        if chunk.choices and chunk.choices[0].delta.content:
            parts.append(chunk.choices[0].delta.content)
    return "".join(parts)

For long answers, you can show text to the user as it arrives instead of collecting it first, by printing the same stream directly:

stream = client.chat.completions.create(
    model=TASK_MODEL["volume"],
    messages=[{"role": "user", "content": "Classify these customer reviews as positive, negative, or neutral."}],
    stream=True,
)
for chunk in stream:
    if chunk.choices and chunk.choices[0].delta.content:
        print(chunk.choices[0].delta.content, end="", flush=True)

For non-urgent Astra work, set the model to openai/gpt-6-astra:batch to get half price, and if you want model selection fully automated, use onysoft/auto (OnyRouter) — routing is free and only the selected model's price applies. Before committing, try all three families side by side with the same prompt in the Playground, and see the API documentation for every parameter. Moving to next month's new flagship will again be a one-line change.

Last updated: September 13, 2026 · Prices: Onysoft live catalog, sale prices as of September 13, 2026; see /models for current pricing.