OpenAI
GPT-5.6 Luna
Cost-efficient GPT-5.6 model for fast, high-volume workloads
- Context
- 1.1M
- Max output
- 128K
- Input / 1M
- $0.20
- Output / 1M
- $1.20
- Output speed
- —
Accepts
- Text input
- Image input
- PDF input
Produces
- Text output
AI model comparison
Compare recorded price, context, output limits, speed, latency, capabilities, and input/output support. Every missing value stays visible, and unsourced benchmarks are excluded.
GPT-5.6 Luna and Step 3.7 Flash both come up when teams are choosing a model for production work, and the honest answer usually depends on your workload rather than a leaderboard. This page puts their published specifications side by side — context window, token pricing, supported inputs and outputs — so you can see where they actually differ.
OpenAI
Cost-efficient GPT-5.6 model for fast, high-volume workloads
Accepts
Produces
StepFun
Newer StepFun flash model for faster agents, coding, and multimodal prompts
Accepts
Produces
At a glance
This is a directional summary of the values recorded in this directory—not a universal quality verdict. Test the finalists on your own prompts before committing.
Where GPT-5.6 Luna leads in recorded data
Where Step 3.7 Flash leads in recorded data
Context capacity
Higher listed limit
GPT-5.6 Luna:1.1M
Step 3.7 Flash:256K
GPT-5.6 Luna
Maximum output
Higher listed limit
GPT-5.6 Luna:128K
Step 3.7 Flash:256K
Step 3.7 Flash
Input price
Lower recorded price
GPT-5.6 Luna:$0.20
Step 3.7 Flash:$0.18
Step 3.7 Flash
Output price
Lower recorded price
GPT-5.6 Luna:$1.20
Step 3.7 Flash:$1.11
Step 3.7 Flash
Output speed
Higher recorded throughput
GPT-5.6 Luna:—
Step 3.7 Flash:—
No complete comparison
Time to first token
Lower recorded latency
GPT-5.6 Luna:—
Step 3.7 Flash:—
No complete comparison
Intelligence Index
Higher directory index
GPT-5.6 Luna:—
Step 3.7 Flash:—
No complete comparison
Evidence
A score appears only when both records include a verified source. It is not treated as a universal ranking.
Specifications
| Specification | GPT-5.6 Luna | Step 3.7 Flash |
|---|---|---|
| Provider | OpenAI | StepFun |
| Model family | gpt-luna | — |
| Accepted inputs | text, image, pdf | text, image, video |
| Produced outputs | text | text |
| Context window | 1.1MRecorded lead | 256K |
| Max output | 128K | 256KRecorded lead |
| Intelligence Index | — | — |
| Input price / 1M | $0.20 | $0.18Recorded lead |
| Output price / 1M | $1.20 | $1.11Recorded lead |
| Output speed | — | — |
| Time to first token | — | — |
| Reasoning mode | Documented | Documented |
| Tool calling | Documented | Documented |
| Image input | Documented | Documented |
| Audio input | Not documented | Not documented |
| Structured output | Documented | Not documented |
| License | Proprietary | Open weights |
| Released | Jul 9, 2026 | May 29, 2026 |
Workload guidance
On the published numbers, GPT-5.6 Luna accepts the larger context window and Step 3.7 Flash is cheaper per input token. Which matters more depends on whether your bottleneck is document size or spend — the table above has the exact figures.
Provenance
Prices and hosted performance can change. SyncDev records source references and clearly separates documented specifications from measured values; confirm commercial terms with the provider before deployment.
GPT-5.6 Luna
OpenAI · model record and recorded source
Step 3.7 Flash
StepFun · model record and recorded source
Choose any two approved model records and review them with the same evidence rules.