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Model comparison

GPT-6 Sol vs GPT-5.6 Sol: half the price, same cache rules

GPT-6 Sol costs half as much as GPT-5.6 Sol on every rate, and Codex suggests the move. What changes, what the promo pricing means, and what stays put.

· Prices as of September 28, 2026

  • GPT-6 Sol

    OpenAI · Released September 22, 2026

    The mid-priced GPT-6 model, which OpenAI pitches for complex coding and agent workflows and which the Codex docs recommend for complex coding.

    GPT-6 Sol facts and comparisons

  • GPT-5.6 Sol

    OpenAI · Released July 9, 2026 · Previous generation

    The flagship of the July 2026 GPT-5.6 family, now succeeded by GPT-6 Sol and on promotional pricing.

    GPT-5.6 Sol facts and comparisons

The short answer

GPT-6 Sol costs half as much as GPT-5.6 Sol on input, output, cache writes, and cache hits, so the example agentic coding session drops from $4.20 to $2.10. Both bill cache writes at 1.25x input, so the saving holds on cached and uncached work alike. Codex suggests moving from GPT-5.6 Sol to GPT-6 Sol, though Codex cloud chats on ChatGPT plans still run GPT-5.6 Sol.

Choose GPT-6 Sol if

  • You pay API rates and want the same session for $2.10 instead of $4.20.
  • You use Codex locally and want the model Codex suggests moving to, which its docs also recommend for complex coding.
  • Accuracy matters to you, and you want the model OpenAI says makes about half as many mistakes as its predecessor on its internal factuality evaluation.

Choose GPT-5.6 Sol if

  • You depend on behavior OpenAI documented for GPT-5.6 Sol, such as programmatic tool calling, and want to validate GPT-6 Sol before switching.
  • You work in Codex cloud on a ChatGPT plan, where chats run GPT-5.6 Sol.
  • Your code calls the API id gpt-5.6, which points to GPT-5.6 Sol, and you are not ready to change it.

Side by side

Specs and prices

FactGPT-6 SolGPT-5.6 Sol
MakerOpenAIOpenAI
API model idgpt-6-solgpt-5.6-sol
ReleasedSeptember 22, 2026July 9, 2026
StatusCurrentPrevious generation
Context window1.05M tokens1.05M tokens
Max output128K tokens128K tokens
Open weightsNoNo
Input, per 1M tokens$2$4
Cache hit, per 1M$0.20$0.40
Cache write, per 1M$2.50$5
Output, per 1M tokens$10$20
Runs inCodex, OpenCode, OpenRouter, and GitHub CopilotCodex, Cursor, OpenCode, OpenRouter, and GitHub Copilot

Standard API rates in US dollars, as published by each maker on September 28, 2026. Batch and priority tiers, taxes, and subscription plans are not included. GPT-6 Sol: Requests over 272K input tokens cost 2x for input and cache and 1.5x for output, for the whole request. GPT-5.6 Sol: Requests over 272K input tokens cost 2x for input and cache and 1.5x for output, for the whole request. These are promotional rates, available at least through November 21, 2026.

Cost

What the same work costs

The same token counts, priced at each model’s published rates. Cached tokens are billed at each maker’s cache prices, so the session shows what caching is worth on each model.

Real sessions differ: the two models count the same code as different numbers of tokens, and reasoning settings change how much each one writes. Your own history is the real test.

Example workload costs
WorkloadGPT-6 SolGPT-5.6 Sol
Agentic coding session, 100K input, 400K written to cache, 2M read from cache, 50K output$2.10$4.20
Large one-off review, 150K input with no cache hits, 10K output$0.40$0.80
Output-heavy generation, 30K input, 80K output$0.86$1.72
A month of sessions, 110 sessions: 5 a day, 22 working days$231.00$462.00
Where the session’s cost goes
Cache writes$1.00$2.00
Cache reads$0.40$0.80
Uncached input$0.20$0.40
Output$0.50$1.00
caching saves on the session with GPT-6 Sol (62%)
$3.40
caching saves on the session with GPT-5.6 Sol (62%)
$6.80

What does upgrading from GPT-5.6 Sol to GPT-6 Sol save?

Exactly half, line for line. GPT-5.6 Sol bills $4 per million input tokens, $0.40 per million cached tokens, $5 per million cache-write tokens, and $20 per million output tokens. GPT-6 Sol charges $2 for input and $10 for output, with writes at $2.50 and hits at $0.20.

Because both generations follow the same caching rules, the halving carries through every workload. The example session costs $4.20 on GPT-5.6 Sol and $2.10 on GPT-6 Sol. The uncached review drops from $0.80 to $0.40, and the output-heavy generation from $1.72 to $0.86. Over 110 sessions a month that is $462.00 against $231.00.

On both, 48% of the session goes to cache writes. Writing 400K tokens to the cache costs $2.00 on GPT-5.6 Sol and $1.00 on GPT-6 Sol. Caching still saves 62% on each compared with sending the same tokens uncached: $6.80 and $3.40 in dollars.

Does GPT-5.6 Sol's promotional price last?

OpenAI lists GPT-5.6 Sol's current rates as promotional, available at least through November 21, 2026. The sources behind this page do not say what GPT-5.6 Sol will cost after that, so treat the 2x gap as today's figure rather than a permanent one.

GPT-6 Sol's rates carry no promotional note. For a pipeline you expect to run for months, that is one more reason to plan the move instead of relying on GPT-5.6 Sol's current price.

Where GPT-5.6 Sol still shows up

GPT-5.6 Sol is a previous-generation model now, but it has not disappeared. Codex cloud chats on ChatGPT plans run it, and the API id gpt-5.6 points to it. Scripts that call gpt-5.6 stay on GPT-5.6 Sol and its promotional rates until you change the id.

Elsewhere in Codex the suggestion is to move to GPT-6 Sol, which defaults to medium reasoning effort in the API and in Codex. OpenAI pitches it for complex coding and agentic workflows and reports about half as many mistakes as its predecessor on its internal factuality evaluation.

OpenAI's claims for GPT-5.6 Sol centered on token efficiency, better frontend layout and design judgment, and programmatic tool calling, where the model writes JavaScript that calls tools and processes their output. Output length drives cost, so run your own tasks on both before assuming the token counts match.

Both share a 1.05M context window, 128K of output, and the 272K long-context line, above which a request costs 2x for input and cache and 1.5x for output. EveryToken prices your local Codex history at these rates, per model, so the before and after of a switch is easy to read.

Prompt caching

How OpenAI bills cached tokens

OpenAI

Prompt caching is on by default. From GPT-5.6 on you can also mark up to four explicit cache breakpoints, while GPT-5.5 and earlier cache automatically only.

From GPT-5.6 on, a cache write costs 1.25x the uncached input price and a cache hit costs 0.1x. GPT-5.5 and earlier add no charge for writing the cache: written tokens are billed as ordinary input, and a hit costs 0.1x on the models compared here.

On GPT-5.6 and later, a cached prefix stays reusable for at least 30 minutes after its last use, and caching starts at 1,024 input tokens.

Source: OpenAI: Prompt caching

Your own numbers

See what GPT-6 Sol and GPT-5.6 Sol really cost you.

everyaitoken reads your Codex, OpenCode, OpenRouter, and Cursor history on your Mac and prices every request at API rates, with what caching saved or cost. $9 once.

Launching soonSee the cache math

FAQ

Questions

Is GPT-6 Sol cheaper than GPT-5.6 Sol?

Yes, by half on every rate: $2 against $4 for input and $10 against $20 for output. GPT-5.6 Sol's rates are promotional and available at least through November 21, 2026.

Does the API id gpt-5.6 point to GPT-6 Sol?

No. The API id gpt-5.6 points to GPT-5.6 Sol. To use the newer model, call gpt-6-sol.

Which Sol model does Codex cloud use?

On ChatGPT plans, Codex cloud chats run on GPT-5.6 Sol. Elsewhere, Codex suggests moving from GPT-5.6 Sol to GPT-6 Sol.

Do GPT-6 Sol and GPT-5.6 Sol cache the same way?

Yes. Both belong to the generations where OpenAI bills cache writes at 1.25x input and cache hits at 0.1x, with up to four explicit cache breakpoints. That is why the price gap is identical on cached and uncached work.

Sources

  1. OpenAI: API pricing
  2. OpenAI docs: GPT-6 Sol
  3. OpenAI: Introducing GPT-6 Sol and Luna
  4. OpenAI: API changelog
  5. Codex docs: Models
  6. OpenRouter: GPT-6 Sol
  7. OpenCode docs: Zen
  8. GitHub Docs: Supported AI models in Copilot
  9. OpenAI docs: GPT-5.6 Sol
  10. OpenAI: Using GPT-5.6
  11. Codex docs: Pricing
  12. Cursor docs: Models and pricing
  13. OpenRouter: GPT-5.6 Sol
  14. OpenAI: Prompt caching

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