OpenAI: GPT-5.3-Codex

openai/gpt-5.3-codex · OpenAINot yet established

Declared family: GPT
Evidence confidence: Unknown
Declared tokenizer tag: GPT
Entered catalogue: 24 February 2026
Last tested: Not yet measured
Measurement: Awaiting measurement

Evidence stack

Signals of different kinds, weighed together

Signal	Result	Reference
Tokenizer signature	Not measured	–
API surface	Identical contract to 4 other entries	api_f0db61b1
Context and output	400,000 context · 128,000 max output	declared
Reasoning contract	Optional · efforts xhigh, high, medium, low, none · default medium	declared
Serving providers observed	None recorded yet	–

Declared record

What the catalogue claims about this model

GPT-5.3-Codex is OpenAI’s most advanced agentic coding model, combining the frontier software engineering performance of GPT-5.2-Codex with the broader reasoning and professional knowledge capabilities of GPT-5.2. It achieves state-of-the-art results...

Modalities: text+image+file->text
Declared tokenizer: GPT
Prompt price: $1.75 / M tokens
Completion price: $14.0 / M tokens

Supported parameters

include_reasoningmax_completion_tokensmax_tokensreasoningreasoning_effortresponse_formatseedstructured_outputstool_choicetools

defaults: {"temperature":null,"top_p":null,"top_k":null,"frequency_penalty":null,"presence_penalty":null,"repetition_penalty":null}

Catalogue entry

History

Every observation, kept as taken

24 February 2026Enters the OpenRouter catalogue declared as GPT.

Cite this page as the evidence record for OpenAI: GPT-5.3-Codex: the URL is stable, measurements are dated, and revisions append to the history above. Method: tokenizer fingerprinting, v1, 50 strings. The raw data behind every figure is on the data page.