Model Comparison
GPT-5.3 Chat vs GPT-5.6 LunaWhich is better in 2026?
GPT-5.6 Luna significantly outperforms across most benchmarks. GPT-5.6 Luna is 2.1x cheaper per token.
Verdict: GPT-5.3 Chat vs GPT-5.6 Luna — which is better?
GPT-5.3 Chat (by OpenAI) and GPT-5.6 Luna (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-5.3 Chat outperforms in 0 benchmarks, while GPT-5.6 Luna is better at 2 benchmarks (HealthBench, HealthBench Hard). GPT-5.6 Luna significantly outperforms across most benchmarks.
On price, GPT-5.6 Luna is roughly 2.1x 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-5.3 Chat if…
- you want predictable pricing at $1.75/M input and $14.00/M output
Choose GPT-5.6 Luna if…
- you want the strongest raw capability — it leads on 2 of 2 shared benchmarks
- cost matters — it's about 2.1x 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
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.3 Chat outperforms in 0 benchmarks, while GPT-5.6 Luna is better at 2 benchmarks (HealthBench, HealthBench Hard).
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-5.3 Chat ($1.75/1M tokens) is 1.8x more expensive than GPT-5.6 Luna ($1.00/1M tokens).
For output processing, GPT-5.3 Chat ($14.00/1M tokens) is 2.3x more expensive than GPT-5.6 Luna ($6.00/1M tokens).
In conclusion, GPT-5.3 Chat 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-5.3 Chat's 128,000 tokens. GPT-5.6 Luna can generate longer responses up to 128,000 tokens, while GPT-5.3 Chat is limited to 16,384 tokens.
Input Capabilities
Supported data types and modalities
Both GPT-5.3 Chat and GPT-5.6 Luna support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
GPT-5.3 Chat
GPT-5.6 Luna
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-5.3 Chat was released on 2026-03-04, while GPT-5.6 Luna was released on 2026-07-09.
GPT-5.6 Luna is 4 months newer than GPT-5.3 Chat.
Mar 4, 2026
4 months ago
Jul 9, 2026
2 weeks ago
4mo newerKnowledge Cutoff
When training data ends
GPT-5.3 Chat has a knowledge cutoff of 2025-08-31, while GPT-5.6 Luna has a cutoff of 2026-02-16.
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-5.3 Chat (2025-08-31).
Aug 2025
Feb 2026
6 mo newerProvider Availability
GPT-5.3 Chat is available from OpenAI. GPT-5.6 Luna is available from OpenAI.
GPT-5.3 Chat
GPT-5.6 Luna
Outputs Comparison
Key Takeaways
GPT-5.3 Chat
View detailsOpenAI
No standout differentiators in the data we have for this pair.
GPT-5.6 Luna
View detailsOpenAI
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.3 Chat and GPT-5.6 Luna side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.3 Chat vs GPT-5.6 Luna.