GPT-5.6 Luna vs GPT-5.5 Instant
Benchmarks, API Token Pricing, Context Window & Speed Comparison
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GPT-5.6 Luna by OpenAI and GPT-5.5 Instant by OpenAI represent two of the frontier AI models analyzed in our comprehensive 2026 AI benchmark and LLM comparison. In this head-to-head evaluation, we examine API token pricing, context window specifications, inference speed (tokens per second), and empirical reasoning performance. From a pure economic perspective, GPT-5.6 Luna holds a notable pricing advantage for token ingestion. On output generation, GPT-5.6 Luna is more economical per million generated tokens. In data-heavy architectures requiring extensive repository or document analysis, GPT-5.6 Luna provides an expanded memory horizon with 1,050K tokens. In latency-sensitive production environments, GPT-5.6 Luna leads in tokens-per-second throughput, making it ideal for real-time conversational agents and high-concurrency workflows. Below is the complete empirical head-to-head breakdown across cost, speed, context, and capability matrices.
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GPT-5.6 Luna
Efficient 5.6An economical GPT-5.6 tier for fast, high-volume work.
$0.20 / 1M
$1.20 / 1M
1.05M tokens
63.5%
GPT-5.5 Instant
Low-Latency 5.5A compact GPT for low-latency assistance and high-volume workloads.
$0.75 / 1M
$6.00 / 1M
400K tokens
74.5%
Key Differences at a Glance
- GPT-5.6 Luna is 4.7x cheaper for API usage (input + output tokens combined).
- GPT-5.6 Luna has a larger context window (1M vs 400K tokens).
- GPT-5.6 Luna is faster at 230 tok/s vs 168 tok/s.
- GPT-5.5 Instant leads on SWE-bench coding (74.5% vs 63.5%).
| Feature | GPT-5.6 Luna | GPT-5.5 Instant |
|---|---|---|
Intelligence Index Composite reasoning & knowledge score (0-100) | 57 | 65 |
Provider | OpenAI | OpenAI |
Input Price Cost per million input tokens | $0.20 / 1M | $0.75 / 1M |
Output Price Cost per million output tokens | $1.20 / 1M | $6.00 / 1M |
Blended Price Weighted 7:2:1 cache:input:output per 1M | $0.17 / 1M | $0.80 / 1M |
Context Window Maximum input + output tokens | 1.05M tokens~1,575 A4 pages of text | 400K tokens~600 A4 pages of text |
Max Output Tokens Per single request | 128K | 128K |
Throughput Speed Tokens generated per second | 230 tok/s | 168 tok/s |
SWE-bench Verified Real-world software engineering | 63.5% | 74.5% |
GPQA Diamond Graduate-level reasoning | 70.5% | 75% |
Cached Input Price Prompt caching discount per 1M tokens | $0.02 / 1M | $0.07 / 1M |
Who Wins Where?
At-a-glance decision frameworkEmpirical Head-to-Head Benchmark Scores
Official evaluation metrics verified by independent third-party research labs.
Industry benchmark evaluating real-world GitHub issue resolution and multi-file debugging.
Challenging questions created by domain experts to test complex PhD-level reasoning.
Hardened reasoning and academic knowledge benchmark with reduced lucky-guess probability.
Crowdsourced human preference evaluation based on blind, head-to-head model battles.
Extremely difficult, closed-ended questions spanning the frontier of human expert knowledge.
Autonomous multi-step tasks executed inside a real command-line terminal environment.
Research-grade coding problems drawn from real scientific and numerical workloads.
Contamination-free competitive programming problems collected continuously over time.
American Invitational Mathematics Examination — multi-step Olympiad-level reasoning.
Accuracy when reasoning over very large inputs that fill the model context window.
Tokens emitted per second during active generation streaming.
Latency & Response Time
Time to first token (TTFT) and estimated end-to-end response time for a typical 500-token response.
Real-Time Interactive Token Cost Simulator
Adjust sliders to calculate projected monthly cloud API spending with prompt caching discounts.
GPT-5.6 Luna · Strengths & Key Advantages
- Very cheap while keeping the 1M context window
- Fast enough for real-time pipelines
- Very strong throughput per dollar
Considerations & Trade-offs
- Weak reasoning relative to the Sol and Terra tiers
- Not suitable for complex analysis or long plans
GPT-5.5 Instant · Strengths & Key Advantages
- Low latency for interactive agents
- Good capability for the price band
- Noticeably lower latency than the full GPT-5.5 tier
Considerations & Trade-offs
- Shallower reasoning than full GPT-5.5
- Struggles with very long multi-step plans
Token Use & Task Economics
Estimated cost and token consumption to complete one representative agentic task.
| Metric | GPT-5.6 Luna | GPT-5.5 Instant |
|---|---|---|
Cost per Task Estimated USD to finish one task | $0.19 | $0.95 |
Output Tokens / Task Tokens generated per task | 46K | 52K |
Reasoning Tokens / Task Thinking tokens burned per task | 20K | 26K |
Technical Specifications
Architecture, release timeline, capabilities, and modalities.
| Feature | GPT-5.6 Luna | GPT-5.5 Instant |
|---|---|---|
| Official API Model ID (SDK) | gpt-5-6-luna | gpt-5-5-instant |
| API Protocol | OpenAI Responses API & Chat Completions v1 | OpenAI Responses API & Chat Completions v1 |
| Release Date | 2026-07 | 2026-05 |
| Knowledge Cutoff | February 2026 | December 2025 |
| Architecture | Efficient compact reasoning model | Low-latency compact reasoning model |
| Parameters | Confidential | Confidential |
| Enterprise Rate Limits (RPM / TPM) | 10,000 – 30,000 RPM (Tier 5 Enterprise) · 4,000,000 – 10,000,000 TPM | 10,000 – 30,000 RPM (Tier 5 Enterprise) · 800,000 – 2,000,000 TPM |
| Long-Context Tier (>128K/200K) | Flat rate ($0.2/1M in) across full 1050K window | Flat rate ($0.75/1M in) across full 400K window |
| Prompt Cache Policy & TTL | Automatic prefix caching at $0.02/1M (no extra cache-write fee) | Automatic prefix caching at $0.075/1M (no extra cache-write fee) |
| Computer Use / GUI Agent | Supported (Screen coordinate grounding, browser & desktop GUI action loops) | Supported (Screen coordinate grounding, browser & desktop GUI action loops) |
| MCP & Parallel Tool Calling | Native MCP Client/Server ready · Parallel function calling · 100% Strict JSON Schema | Native MCP Client/Server ready · Parallel function calling · 100% Strict JSON Schema |
| Web Search Grounding & Sandbox | Native Web Search tool + Hosted Code Interpreter & File Search RAG | Native Web Search tool + Hosted Code Interpreter & File Search RAG |
| Official Fine-Tuning Support | Supervised Fine-Tuning (SFT), Direct Preference (DPO) & Reinforcement Fine-Tuning (RFT) | Supervised Fine-Tuning (SFT), Direct Preference (DPO) & Reinforcement Fine-Tuning (RFT) |
| Multimodal Token Billing | Text BPE (~4 chars/token) · Vision (~258–765 tokens per image tile) | Text BPE (~4 chars/token) · Vision (~258–765 tokens per image tile) |
| Quantization & Min GPU VRAM | Cloud-Hosted Proprietary (FP8 / BF16 Tensor Core Cluster) · Zero Local VRAM Required (100% Serverless Cloud API) | Cloud-Hosted Proprietary (FP8 / BF16 Tensor Core Cluster) · Zero Local VRAM Required (100% Serverless Cloud API) |
| Safety & Frontier Classification | OpenAI Preparedness Framework Audited & System Card Published | OpenAI Preparedness Framework Audited & System Card Published |
| Enterprise Compliance (ZDR/HIPAA/SOC2) | SOC2 Type II · GDPR · Zero Data Retention (ZDR) & HIPAA BAA Available on Enterprise Tier | SOC2 Type II · GDPR · Zero Data Retention (ZDR) & HIPAA BAA Available on Enterprise Tier |
| Input Modalities | text, vision | text, vision |
| Output Modalities | text | text |
GPT-5.6 Luna vs GPT-5.5 Instant: Quick Answers
Which is more intelligent, GPT-5.6 Luna or GPT-5.5 Instant?
GPT-5.5 Instant is more intelligent. It scores 65 compared with 57 on the composite Intelligence Index.
Which model is faster?
GPT-5.6 Luna is faster, generating 230 tokens per second compared with 168 tokens per second.
Which model is cheaper to run?
GPT-5.6 Luna is cheaper at $0.17 per 1M tokens blended, compared with $0.80 (7:2:1 cache:input:output ratio).
Which model has lower latency?
GPT-5.6 Luna has lower latency, with a time to first token of 0.42s compared with 0.78s.
Which model has a larger context window?
GPT-5.6 Luna has a larger context window, supporting 1.05M tokens compared with 400K tokens.
Verdict
Verdict & Model Selection Recommendation: Choose GPT-5.6 Luna if your priority is High-throughput classification, extraction and routing. Its performance in demanding tasks justifies its operational token cost. Choose GPT-5.5 Instant if your workflow prioritizes Interactive assistants and latency-sensitive routing. For large-scale batch processing or customer-facing conversational interfaces, its balance of speed and economics delivers superior ROI.
Frequently asked questions
How does GPT-5.6 Luna compare to GPT-5.5 Instant in API token pricing and cost per token?+
GPT-5.6 Luna costs $0.20 per 1M input tokens and $1.20 per 1M output tokens, whereas GPT-5.5 Instant costs $0.75 input and $6.00 output. Overall, GPT-5.6 Luna is the more cost-effective model for high-volume API pipelines. Both models support prompt caching discounts of up to 90% for repeated prompt prefixes.
Which model has a larger context window: GPT-5.6 Luna or GPT-5.5 Instant?+
GPT-5.6 Luna supports a context window of 1,050K tokens (~788k words), while GPT-5.5 Instant supports 400K tokens (~300k words). Therefore, GPT-5.6 Luna can process more textual data and document context in a single prompt.
Which AI model is better for software engineering and coding: GPT-5.6 Luna or GPT-5.5 Instant?+
GPT-5.6 Luna scores 63.5% on SWE-bench Verified while GPT-5.5 Instant scores 74.5%. For autonomous software engineering and multi-file debugging, GPT-5.5 Instant holds the verified benchmark lead.
What is the difference in reasoning capability and extended thinking between GPT-5.6 Luna and GPT-5.5 Instant?+
GPT-5.6 Luna features native chain-of-thought extended thinking mode with configurable reasoning effort. In contrast, GPT-5.5 Instant provides chain-of-thought reasoning depth for complex math and science.
How does inference speed (tokens per second) compare between GPT-5.6 Luna and GPT-5.5 Instant?+
GPT-5.6 Luna generates approximately 230 tokens per second, while GPT-5.5 Instant delivers 168 tokens per second. In latency-sensitive production environments, GPT-5.6 Luna provides faster time-to-first-token (TTFT) and higher streaming response velocity.
Can you implement a tiered LLM routing setup combining GPT-5.6 Luna and GPT-5.5 Instant to optimize costs?+
Yes! High-efficiency architectures route high-frequency routine classification and conversational tasks to GPT-5.6 Luna to save operational costs, and dynamically escalate complex architectural queries or reasoning tasks to GPT-5.5 Instant. This tiered routing pattern cuts overall API bills by up to 70%.
Understand key metrics like context window, token pricing, reasoning mode, and SWE-bench scores in our comprehensive AI glossary.
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Benchmark scores, token prices, and rate limits evolve rapidly as AI labs release model updates. Always verify current specifications and pricing on the official provider documentation.
Sources: GetInfoUs Independent AI Benchmarks & Official API Specs