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// gpt

GPT-5.6 Sol

The full-size GPT-5.6. Frontier reasoning, priced like a mid-tier.

GPT-5.6 Sol is the flagship of the GPT-5.6 line and OpenAI’s current frontier reasoning model. It sits at the same list price as Claude Opus 5 ($5/$30 per M) but brings OpenAI’s mature function-calling ecosystem and the widest third-party tool support.

The 5.6 generation brought significant improvements in long-context recall and multi-step reasoning over GPT-5.5, while keeping the same 1M+ token window. That makes Sol the model to reach for when the task is genuinely hard - complex refactors, research synthesis, agent workflows where one mistake poisons the chain.

We sell it at half OpenAI’s list price. Same model, same API shape, same tool ecosystem - the discount is on the invoice.

Official list
llmrelay
Input / M tokens
$5.00
$2.50
Output / M tokens
$30.00
$15.00
Context window
—
1,050,000 tokens
Max output
—
128,000 tokens

What it costs you per month

Real-world budget scenarios. Numbers are simple sums — official list price vs llmrelay's 50% off tier.

Usage scenario
Official
llmrelay
Light coding (1M in / 200K out per month)
$11.00
$5.50save $5.50
Heavy Cursor / Cline user (50M in / 5M out per month)
$400.00
$200.00save $200.00
Production RAG (500M in / 20M out per month)
$3100.00
$1550.00save $1550.00

What it's good at

Best for

Pick GPT-5.6 Sol when

  • +You are already in the OpenAI ecosystem and escalating to the flagship tier. Sol speaks the same API as GPT-5.6 Terra and Luna, so moving between tiers is one model-id change.
  • +Function calling and structured output matter. OpenAI’s tool-use implementation is the most mature and widely supported, so if your workflow leans on that, Sol is the flagship option.
  • +Long-context reasoning where you need synthesis rather than extraction. Sol handles the full 1M window and can pull findings across it, not just retrieve.
  • +You need a second opinion on work done by Claude. Running the same prompt through both families catches model-specific blind spots.

Choose something else when

  • !You do not need frontier reasoning. Terra and Luna are half and a quarter of the per-token cost, and for most work the capability gap does not justify the spend. Start cheaper and escalate where you see it fail.
  • !Paying Sol rates for ordinary copy. Fable is not a writing SKU. For hard Claude work use Opus 5 or Fable 5.1; for cheap volume use Luna or Haiku.
  • !You are optimising for cost above all. Claude Sonnet 5 is $1/M input against Sol’s $2.50, and on many tasks it is good enough.
  • !High-volume batch work. The per-call premium adds up fast when you are running millions of inferences. Classification and tagging are Luna or Haiku jobs, not Sol jobs.

Questions people ask about GPT-5.6 Sol

How much does GPT-5.6 Sol cost?

OpenAI’s list price is $5.00 per million input tokens and $30.00 per million output tokens. On llmrelay it is $2.50 and $15.00 - exactly half list. Billing is prepaid per token from one credit pool, with no subscription.

Should I use GPT-5.6 Sol or Claude Opus 5?

Both are flagship models at the same list price, and on llmrelay both cost $2.50/M input. The choice comes down to ecosystem: if your workflow is built around OpenAI function calling and you have existing tool integrations, Sol is the natural pick. If you prioritise depth of review and are not locked into OpenAI tooling, Opus 5 is a strong alternative. Run the same task through both and pick the one that gives you better output.

Is Sol worth it over Terra?

Sometimes. Terra costs half as much per token and handles most reasoning tasks well. Sol earns its price on problems where breadth of findings matters - security review, migration planning, anything where missing a corner case is expensive. Start on Terra and escalate to Sol when you see it fall short.

What is the context window on GPT-5.6 Sol?

1,050,000 tokens input, with up to 128,000 output tokens. That is slightly larger than Claude’s 1M window, though the difference is small enough that it rarely matters in practice.

Try GPT-5.6 Sol at half the price

Free to create an account, no subscription, $10 minimum top-up — enough to run this model against a real task and judge quality yourself.

Get API key →

Compare GPT-5.6 Sol against the alternatives

The comparisons this model appears in, the models nearest it on price, and the full rate card.