AI Desk · Model Identity · Compare
OpenAI: GPT-5 Nano · OpenAI: GPT-5.6 Luna
Identity similarity: very highExact tokenizer agreement · 50/50Exact agreement across every measured string is strong evidence of shared tokenizer lineage. It shows shared ancestry, and does not on its own establish that these are the same release.
OpenAI: GPT-5 Nano recordOpenAI: GPT-5.6 Luna recordOpen in the interactive bench
Tokenizer fingerprint
50 of 50 mutually clean strings agree| Test string | OpenAI: GPT-5 Nano | OpenAI: GPT-5.6 Luna | Verdict |
|---|---|---|---|
| en-prose | 14 | 14 | match |
| en-long | 17 | 17 | match |
| spaces-20 | 3 | 3 | match |
| spaces-60 | 3 | 3 | match |
| tabs-20 | 3 | 3 | match |
| newlines-20 | 4 | 4 | match |
| mixed-ws | 6 | 6 | match |
| digits-9 | 3 | 3 | match |
| digits-12 | 4 | 4 | match |
| digits-30 | 10 | 10 | match |
| digits-sep | 7 | 7 | match |
| float-long | 9 | 9 | match |
| zh-common | 12 | 12 | match |
| zh-long | 17 | 17 | match |
| zh-rare | 20 | 20 | match |
| ja-kana | 10 | 10 | match |
| ja-kanji | 13 | 13 | match |
| ko | 11 | 11 | match |
| ru | 11 | 11 | match |
| ar | 11 | 11 | match |
| he | 10 | 10 | match |
| hi | 11 | 11 | match |
| th | 11 | 11 | match |
| el | 14 | 14 | match |
| emoji-basic | 8 | 8 | match |
| emoji-skin | 13 | 13 | match |
| emoji-zwj-family | 11 | 11 | match |
| emoji-zwj-x3 | 33 | 33 | match |
| emoji-flags | 16 | 16 | match |
| emoji-prof | 20 | 20 | match |
| math | 31 | 31 | match |
| boxdraw | 27 | 27 | match |
| combining | 11 | 11 | match |
| cjk-ext-b | 13 | 13 | match |
| surrogates | 40 | 40 | match |
| zalgo | 35 | 35 | match |
| rtl-mix | 5 | 5 | match |
| py-code | 25 | 25 | match |
| py-indent | 15 | 15 | match |
| json | 20 | 20 | match |
| html | 16 | 16 | match |
| regex | 44 | 44 | match |
| camel | 6 | 6 | match |
| snake | 6 | 6 | match |
| rare-word-x5 | 31 | 31 | match |
| repeat-tok | 22 | 22 | match |
| base64 | 34 | 34 | match |
| hex | 11 | 11 | match |
| url | 17 | 17 | match |
| uuid | 27 | 27 | match |
Values are the marginal prompt-token cost of each string with the model's fixed overhead subtracted. An x marks a row excluded as corrupt for that model.
API surface
The declared serving contracts differ| Field | OpenAI: GPT-5 Nano | OpenAI: GPT-5.6 Luna | Verdict |
|---|---|---|---|
| Context length | 400000 | 1050000 | × differs |
| Max output tokens | 128000 | 128000 | ✓ match |
| Supported parameters | include_reasoning, max_completion_tokens, max_tokens, reasoning, reasoning_effort, response_format, seed, structured_outputs, tool_choice, tools | include_reasoning, max_completion_tokens, max_tokens, reasoning, reasoning_effort, response_format, seed, structured_outputs, tool_choice, tools | ✓ match |
| Defaults | {"temperature":null,"top_p":null,"top_k":null,"frequency_penalty":null,"presence_penalty":null,"repetition_penalty":null} | {"temperature":null,"top_p":null,"top_k":null,"frequency_penalty":null,"presence_penalty":null,"repetition_penalty":null} | ✓ match |
| Reasoning contract | {"mandatory":true,"supported_efforts":["high","medium","low","minimal"],"default_effort":"medium"} | {"mandatory":false,"default_enabled":true,"supported_efforts":["max","xhigh","high","medium","low","none"],"default_effort":"medium"} | × differs |
| Modalities | text+image+file->text | text+image+file->text | ✓ match |
Method: tokenizer fingerprinting, v1, 50 strings. Raw data on the data page. This page is static and dated; the interactive bench compares any two of the 422 catalogue models.