Model Comparison
GPT-5.6 Luna vs GPT-5.5 InstantWhich is better in 2026?
GPT-5.6 Luna significantly outperforms across most benchmarks. GPT-5.6 Luna is 5.0x cheaper per token.
Verdict: GPT-5.6 Luna vs GPT-5.5 Instant — which is better?
GPT-5.6 Luna (by OpenAI) and GPT-5.5 Instant (by OpenAI) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.
GPT-5.6 Luna outperforms in 6 benchmarks (GPQA, HealthBench, HealthBench Consensus, HealthBench Hard, HealthBench Professional, MMMU-Pro), while GPT-5.5 Instant is better at 0 benchmarks. GPT-5.6 Luna significantly outperforms across most benchmarks.
On price, GPT-5.6 Luna is roughly 5.0x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT-5.6 Luna also accepts a larger context window (1,050,000 input tokens), making it the stronger choice for long documents and large codebases.
Choose GPT-5.6 Luna if…
- you want the strongest raw capability — it leads on 6 of 6 shared benchmarks
- cost matters — it's about 5.0x cheaper per token
- you process long inputs — it offers a 1,050,000 token context window
- you want the most recent training data — it shipped Jul 2026
Choose GPT-5.5 Instant if…
- you want predictable pricing at $5.00/M input and $30.00/M output
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.6 Luna outperforms in 6 benchmarks (GPQA, HealthBench, HealthBench Consensus, HealthBench Hard, HealthBench Professional, MMMU-Pro), while GPT-5.5 Instant is better at 0 benchmarks.
GPT-5.6 Luna significantly outperforms across most benchmarks.
Arena Performance
Human preference votes
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-5.6 Luna ($1.00/1M tokens) is 5.0x cheaper than GPT-5.5 Instant ($5.00/1M tokens).
For output processing, GPT-5.6 Luna ($6.00/1M tokens) is 5.0x cheaper than GPT-5.5 Instant ($30.00/1M tokens).
In conclusion, GPT-5.5 Instant is more expensive than GPT-5.6 Luna.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
GPT-5.6 Luna accepts 1,050,000 input tokens compared to GPT-5.5 Instant's 400,000 tokens. Both models can generate responses up to 128,000 tokens.
Input Capabilities
Supported data types and modalities
Both GPT-5.6 Luna and GPT-5.5 Instant support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-5.6 Luna
GPT-5.5 Instant
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
GPT-5.6 Luna was released on 2026-07-09, while GPT-5.5 Instant was released on 2026-05-05.
GPT-5.6 Luna is 2 months newer than GPT-5.5 Instant.
Jul 9, 2026
1 weeks ago
2mo newerMay 5, 2026
2 months ago
Knowledge Cutoff
When training data ends
GPT-5.6 Luna has a knowledge cutoff of 2026-02-16, while GPT-5.5 Instant has a cutoff of 2025-08-31.
GPT-5.6 Luna has more recent training data (up to 2026-02-16), making it potentially better informed about events through that date compared to GPT-5.5 Instant (2025-08-31).
Feb 2026
6 mo newerAug 2025
Provider Availability
GPT-5.6 Luna is available from OpenAI. GPT-5.5 Instant is available from OpenAI.
GPT-5.6 Luna
GPT-5.5 Instant
Outputs Comparison
Key Takeaways
GPT-5.6 Luna
View detailsOpenAI
No standout differentiators in the data we have for this pair.
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.6 Luna and GPT-5.5 Instant side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.6 Luna vs GPT-5.5 Instant.