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GPT-5.6 Luna — 1.05M Context at the Volume Tier

GPT-5.6 Luna is OpenAI's cost-sensitive tier of the GPT-5.6 family, and the interesting part is what it does not give up: GPT-5.6 Luna carries the same 1,050,000-token context window, the same 128,000-token maximum output and the same six-rung reasoning dial as its frontier sibling. What changes is the price and the depth of thinking you would sensibly ask of it. On reAPI, GPT-5.6 Luna bills below OpenAI's published rate on both input and output.

Highlights
Reasoning effort tiers · tools & JSON mode
Best for
Fast responses, everyday tasks
Input
Chat messages (OpenAI-compatible)
Output
Text, streaming optional
GPT-5.6 Luna

Ask GPT-5.6 Luna

Start with the prompt in the composer or choose an example.

Enter to send · Shift+Enter for a new line

Pricing

Credit-based — 1 credit = $0.001 USD. Pay only for completed generations.

First test cost
$0.00111.12 credits

One 1K-token prompt with a 1K-token answer at the cheapest tier.

Testing budget guide
Add credits
$10
≈ 8928 tests
$50
≈ 44642 tests
$100
≈ 89285 tests
Category
Token pricing
Long context · prompts over 272K tokens
Input
$0.160
Price · 1M tokens
$0.320
Price · 1M tokens
Output
$0.960
Price · 1M tokens
$1.440
Price · 1M tokens
Cache read
$0.016
Price · 1M tokens
$0.032
Price · 1M tokens
Cache write
$0.200
Price · 1M tokens
$0.400
Price · 1M tokens

What is the GPT-5.6 Luna API?

GPT-5.6 Luna is OpenAI's cost-sensitive tier of the GPT-5.6 family, served on reAPI through an OpenAI-compatible /api/v1/chat/completions endpoint. It gives up none of the family's limits — the same 1,050,000-token context window, the same 128,000-token maximum output and the same six reasoning-effort rungs from none to max, defaulting to medium — with text and image input and text output. Billing is per 1M tokens, with input and output priced separately; reasoning tokens count as output.

What you can build with this model

Real-world workflows and production use cases you can build and ship with this model.

GPT-5.6 Luna classifying a queue of documents with reasoning switched off

Classification and extraction, priced for the whole queue

This is the work OpenAI names for the lowest effort setting: fast information retrieval and classification, where reasoning adds latency and nothing else. Turn effort off, constrain the output with a schema, and GPT-5.6 Luna becomes a component rather than an oracle — the same prompt over a million rows, at a rate where the arithmetic still works. The part worth noticing is that dropping to this tier does not shrink your inputs: GPT-5.6 Luna reads the same 1,050,000-token window as the frontier tier, so a long document does not force you back up the price ladder just to fit.

Read the API docs
GPT-5.6 Luna triaging requests and escalating only the hard ones

The cheap first pass in front of an expensive model

Most production traffic is not hard. A two-stage route built on GPT-5.6 Luna — it reads everything and decides what is routine, a dearer model sees only what is not — is the single most effective cost lever available on a chat workload, and it works precisely because the cheap stage here is not a weak model but a smaller tier of the same family with the same limits and the same interface. Same key, same endpoint, one model string apart: escalation is a field in your request, not a second integration.

GPT-5.6 Luna answering a latency-critical request with no reasoning pass

Latency-critical paths where thinking is the wrong tool

Voice, autocomplete, live moderation, anything a human is waiting on: OpenAI's own advice for these is to try low effort first and move to none if required. GPT-5.6 Luna is the tier where that advice is cheapest to follow, and where the speed rating is Fast to begin with. Keep the prompt short, keep the output bounded, and treat effort as the dial you turn before you go looking for a different provider — the family's fast path and its deep path are the same API.

Why reAPI for GPT-5.6 Luna

Below the published rate

OpenAI publishes a per-million-token rate for GPT-5.6 Luna input and output. On reAPI, GPT-5.6 Luna bills below both, and the rates on this page are updated live. No subscription underneath it, no minimum commitment, pay-as-you-go from your reAPI balance. The exact numbers are in the pricing table on this page.

OpenAI-compatible drop-in

GPT-5.6 Luna is served from a standard `/api/v1/chat/completions` endpoint. If your code already speaks that shape, adopting GPT-5.6 Luna is a base URL, a key and a model string — the same SDKs work once the base URL points at reapi.ai. No SDK swap, no bespoke client.

One key across the whole ladder

The same reAPI key that calls GPT-5.6 Luna calls its larger siblings, the Claude and Gemini families, and the open-weight tiers. That is what makes tiered routing practical: the escalation target is a model string, not a second vendor relationship with its own invoice and credentials.

GPT-5.6 Luna vs GPT-5.6 Terra

This is the comparison that actually decides a route, and it is unusually clean because GPT-5.6 Luna and GPT-5.6 Terra share almost everything: same context window, same output ceiling, same effort ladder, same tools, same knowledge cutoff, same endpoint. What differs is the reasoning headroom OpenAI rates each for, the lineage they descend from, and the price. Read the rows below as: does this route need judgement, or does it need throughput?

Capability
GPT-5.6 Luna on reAPI
GPT-5.6 Terra
OpenAI's positioning
Optimised for cost-sensitive, high-volume workloads
Balances intelligence and cost
Reasoning rating
High — the family's entry rating
Higher — one step up
Earlier-generation lineage
Corresponds to the nano tier of earlier GPT-5 families
Corresponds to the mini tier
Rate on reAPI
The lowest of the three tiers — see the pricing table above
Higher than Luna, lower than the frontier tier
Context and output limits
1,050,000-token context, 128,000-token maximum output
Identical — the limits do not change across tiers
Effort ladder and tools
All six rungs, functions, web search, file search, computer use
Identical — the difference is which rungs are worth paying for

Comparison reflects behavior documented on OpenAI's own model pages at the time of writing. Rates are described as relationships rather than amounts; the live numbers for GPT-5.6 Luna are in the pricing table above.

Ship GPT-5.6 Luna in three steps

  1. step 01

    Create a reAPI API key

    Sign in to reAPI and create a key under API keys. That one key reaches GPT-5.6 Luna and every other model on the platform, billed from a single balance.

    Open
  2. step 02

    Point your client at reapi.ai

    Set your base URL to reapi.ai's API and your key to the one you just created. Any client that already speaks OpenAI Chat Completions works unchanged — no SDK swap is needed to reach GPT-5.6 Luna.

    Open
  3. step 03

    Send `gpt-5.6-luna` as the model

    Set the model field to `gpt-5.6-luna` — with the dots — and post your messages. On this tier, set reasoning effort deliberately: the family default is medium, and on high-volume routes none or low is usually what you actually want.

    Open
docs/api/gpt-5-6-luna

API reference

Drop-in code and the full parameter table.

View full reference
curl https://reapi.ai/api/v1/chat/completions \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.6-luna",
    "messages": [
      { "role": "user", "content": "Hello" }
    ],
    "reasoning_effort": "low",
    "stream": true
  }'

Parameter validation failed

Rejected synchronously with the failing field named. Check enum values, ranges, and URL fields — nothing is charged.

Authentication or balance issue

401 means a missing or invalid Bearer key; 402 means the reserve exceeds your balance. Manage keys and credits in the console.

Content or material rejected

Reference material and outputs pass automated moderation. Rejected tasks fail with a clear error and a full refund.

Task failed or timed out

A task that reaches a failed state is never charged — the reserve refunds automatically. Keep the task id and retry when ready.

Frequently asked questions

Common questions about this model.

GPT-5.6 Luna is billed pay-as-you-go per token from your reAPI balance, with separate input and output rates and no subscription. Both sit below OpenAI's published per-token rate. Current numbers are in the pricing table on this page.

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