Short answer: As of September 12, 2026, GPT-5.6 Sol costs $4 per million input tokens and $20 per million output, Claude Opus 5 costs $5/$25, and Grok 4.6 costs $2/$6. OpenAI's new flagship, GPT-6 Astra, sits above all three at $10/$50 and only earns its price on long agent runs. For everyday work Sol is the cheapest frontier all-rounder: 5 million tokens a month runs about $52 on Sol, $65 on Opus 5, and $18 on Grok 4.6.

The July version of this comparison went stale in about six weeks. OpenAI cut GPT-5.6 Sol's list price and shipped GPT-6 Astra above it, and Anthropic moved its top tier to Claude Fable 5.1. If you picked a default model in midsummer from a post that has not been updated since, you are comparing numbers that no longer exist.

Everything below was re-checked against the providers' own pricing pages on September 12, 2026. Costs are computed, not eyeballed.

What Changed Since July

Item	July 2026	September 12, 2026	Source
GPT-5.6 Sol price	$5 in / $30 out	$4 in / $20 out	OpenAI pricing page, verified 2026-09-12
Sol promotional window	not stated	promotional pricing through at least November 21, 2026	OpenAI pricing page
Sol long-context rates	2× input / 1.5× output above 272K	$8 in / $30 out above 272K	OpenAI pricing page
OpenAI flagship	GPT-5.6 Sol	GPT-6 Astra ($10/$50)	OpenAI pricing page
Anthropic top tier	Claude Fable 5	Claude Fable 5.1 ($10/$50)	Anthropic pricing page, verified 2026-09-12
Claude Opus 5 price	$5 in / $25 out	unchanged	Anthropic pricing page
Grok 4.6 price	$2 in / $6 out	unchanged	xAI models page
Grok real-time X access	"built-in"	requires search tools to be enabled	xAI models page

Two corrections matter more than the rest.

Sol is now $4/$20 instead of $5/$30: a 20% cut for input tokens and a third for output. Any cost table still showing $5/$30 overstates a Sol-heavy month by about 30%. The new rate is promotional, listed as available through at least November 21, 2026, so treat it as current rather than permanent.

Grok 4.6's real-time access is not automatic. xAI's models page states that Grok has no access to real-time events without search tools enabled. Ask Grok about this week and you need Web Search or X Search switched on.

What did not change: Opus 5 at $5/$25, Grok 4.6 at $2/$6, and the context windows, 1M for Sol and Opus 5, 500K for Grok.

The Contenders at a Glance

Capability	GPT-5.6 Sol	Claude Opus 5	Grok 4.6	GPT-6 Astra
API price (per 1M in / out)	$4 / $20	$5 / $25	$2 / $6	$10 / $50
Cached input	$0.40	$0.50	not published	$1.00
Context window	1M	1M	500K	1.05M
Long-context pricing	2× input, 1.5× output above 272K	standard	higher rates above 200K input	2× input, 1.5× output above 272K
Coding index (third-party)	no longer leads	~68	not in the top band	~67
Real-time data	limited (Feb 16, 2026 cutoff)	limited	with search tools enabled	limited
Knowledge cutoff	February 16, 2026	not stated on the pricing page	February 1, 2026	not stated on the pricing page
Best for	daily work, drafting, coding velocity	hard refactors, long analysis	cheap agents, research with search on	long agent runs, newest frontier

The coding-index column is deliberately loose. In the current published band, Claude Opus 5, Claude Fable 5.1, and GPT-6 Astra sit within about a point of each other (roughly 67 to 68), and Sol no longer leads it. A one-point gap is noise, not a reason to restructure a workflow.

Pricing Breakdown: What Each Model Actually Costs

Per-token prices hide the number you care about, which is your monthly bill. Here is the same workload priced on each model, assuming a 60/40 input/output split:

Usage level	Tokens/month	Sol	Opus 5	Grok 4.6	Astra
Light	~500K	$5.20	$6.50	$1.80	$13.00
Moderate	~5M	$52.00	$65.00	$18.00	$130.00
Heavy	~20M	$208.00	$260.00	$72.00	$520.00

Caching changes this if your prompts repeat. Sol's cached input is $0.40 per million, a tenth of its input price, and Opus 5's is $0.50. Moving 40% of input tokens into cache reads drops the 5M-token month above from $52.00 to about $47.80. Cache writes cost $5.00 per million on Sol, more than fresh input, so caching pays off with repeated long prefixes only.

The last row is the uncomfortable one. Astra is exactly 2.5× Sol on input and output, a $312 difference at 20M tokens a month that buys reliability in long, tool-heavy runs.

Where GPT-6 Astra Fits

Astra is OpenAI's new top tier: 2.5× Sol's price, with a 1.05M-token context. Most people should not default to it.

Use it when a task is long and expensive to redo: multi-hour agent runs, large-repo refactors, analyses where a wrong answer costs more than the tokens. Benchmark write-ups put Astra in the same band as Claude Fable 5.1 on the Artificial Analysis intelligence index at roughly 40% of the cost per task. That is a cost-per-job argument, not a per-token one.

Skip it for chat, for drafting, and for anything you can retry cheaply. Sol at $4/$20 handles those at 40% of Astra's rate.

When to Use Each Model

GPT-5.6 Sol is the default for most work: first drafts, everyday coding, brainstorming. It is fast, its output reads best, and after the price cut it is the cheapest frontier all-rounder. Skip it for hard multi-file refactors and anything needing current events.

Claude Opus 5 is for work where correctness beats speed: large multi-file changes, contracts and specs, long documents, stubborn bugs. It is slower than Sol and wordier, so give it a length limit. Skip it for quick iteration and casual chat.

Grok 4.6 is the cost play: $2/$6 with 500K context for high-volume agentic work, and with search tools enabled it is the only one here that can see this week's news. Skip it for long documents.

GPT-6 Astra is the escalation path when Sol fails twice. Skip it otherwise.

The Multi-Model Workflow

The useful pattern is not picking a winner. It is sequencing them.

Building a feature: Grok 4.6 (with search on) collects current library and API practice, Sol writes the implementation, Opus 5 reviews for edge cases and security. Writing: Grok gathers what is new, Sol drafts, Opus 5 checks the arguments that carry weight.

Switching models mid-conversation is what makes this practical. If moving from Sol to Opus 5 means re-pasting the thread into a second tab, you stop doing it after a week.

Which Should You Choose?

Your priority	Best option
Lowest cost per token	Grok 4.6 at $2/$6
Cheapest strong all-rounder	GPT-5.6 Sol at $4/$20
Hardest refactors and long analysis	Claude Opus 5
Long agent runs where retries are expensive	GPT-6 Astra
Research that needs this week's information	Grok 4.6 with search tools enabled
Best overall workflow	All of them, in one workspace

What You Give Up with Each Model

Sol's price has an expiry listed on the pricing page, and its long-context rates double above 272K input tokens. Opus 5 is slower and wordier, and Anthropic does not publish a knowledge cutoff next to its prices. Grok 4.6 has the smallest context here and needs search tools on before it knows anything recent. Astra costs 2.5× Sol.

And with any bring-your-own-key setup you manage provider billing yourself. There is no bundled allowance that absorbs a bad month. If you want one flat fee and no dashboards, a subscription is the more honest choice.

FAQ

Which model is best for coding in 2026?

Opus 5 and GPT-6 Astra are within about a point of each other at the top of the published coding index, so the tiebreaker is your workload: Opus 5 for multi-file refactors and review, Astra for long agentic runs. Sol is the fastest and cheapest of the strong options.

Which of these models is cheapest?

Grok 4.6 at $2 per million input tokens and $6 per million output. GPT-5.6 Sol follows at $4/$20, then Claude Opus 5 at $5/$25, then GPT-6 Astra at $10/$50. On a 5M-token month with a 60/40 split that is $18, $52, $65, and $130.

Do these prices include prompt caching?

Caching is a separate line. Sol's cached input is $0.40 per million against $4.00 fresh, Opus 5's is $0.50 against $5.00, and Astra's is $1.00 against $10.00. Cache writes cost more than fresh input, so caching helps with repeated long prefixes and hurts with unique requests.

Can I switch between these models mid-conversation?

Yes, in a workspace that keeps one conversation across providers. You add each provider's API key once, then change the model for the next message without losing the thread. Multimodel Chat does this for OpenAI, Anthropic, and xAI at $2/month, and providers bill your key directly at their own rates.

Is GPT-6 Astra worth 2.5× the price of GPT-5.6 Sol?

For most people, no. It makes sense on long agent runs and expensive-to-retry analysis, where per-task cost can favor it. For drafting, chat, and routine coding, Sol at $4/$20 is the better buy.

See the OpenAI API key setup guide, Anthropic guide, and xAI guide to connect your own keys. For monthly bills worked out three ways, read what the ChatGPT API costs per month. If you are weighing a subscription against per-token billing, the BYOK cost comparison has the crossover math, and DeepSeek V4.1 Flash shows what the cheap end of the market now looks like. Product details and workspace pricing: our pricing page.

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GPT-5.6 Sol vs Claude Opus 5 vs Grok 4.6: 2026 Guide