Is GPT-5.3-Codex better than o3?

On accuracy they are statistically tied: GPT-5.3-Codex scored 82.5% and o3 72.5% on the same 80 questions from open datasets. Similar accuracy; o3 costs less per question.

Which is cheaper, GPT-5.3-Codex or o3?

o3 is cheaper: $0.0088 per question as billed, against $0.01. List prices: GPT-5.3-Codex $1.75 in / $14 out, o3 $2 in / $8 out per million tokens.

Which is faster, GPT-5.3-Codex or o3?

o3 is faster at 163 output tokens per second, against 95. Time to first token: 1.4 s for GPT-5.3-Codex, 1.2 s for o3.

Which has the larger context window, GPT-5.3-Codex or o3?

GPT-5.3-Codex, with 400k tokens against 200k.

Head to head · tested 27 Oct 2026

GPT-5.3-Codex vs o3: accuracy, speed and price

Similar accuracy; o3 costs less per question.

OpenAIGPT-5.3-Codex82.5% score · #3$0.01 per question95 tok/s

OpenAIo372.5% score · #21$0.0088 per question163 tok/s

Verdict

Built from the measurements below

Accuracy is too close to call: GPT-5.3-Codex scored 82.5% and o3 72.5% on the same 80 questions, a gap within what chance alone could produce.
o3 is 1.2× cheaper per question as billed ($0.0088 vs $0.01), reasoning tokens included.
o3 generates text 1.7× faster: 163 tokens per second against 95.
o3 starts answering sooner: 1.2 s to the first token, against 1.4 s for GPT-5.3-Codex.
GPT-5.3-Codex accepts more context: 400k tokens against 200k.

Which should you choose?

Choose GPT-5.3-Codex for a 400k-token context window. Choose o3 for faster streaming and a quicker first token. The widest subject gap is in engineering: GPT-5.3-Codex answered 11 of 15 correctly, o3 8 of 15. With so few questions per subject, treat this as a lead to test on your own prompts, not a result.

Accuracy gap +10.0 points (z = 1.51). A winner is called only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.

Head to head

Same questions, same prompt, same API

Measure	GPT-5.3-Codex	o3	Edge
Verification scoreHigher is better	82.5%	72.5%	Too close to call
Cost per questionLower is better	$0.01	$0.0088	o3
Output speedHigher is better	95	163	o3
Time to first tokenLower is better	1.4 s	1.2 s	o3
End-to-end response timeLower is better	5.2 s	3.9 s	o3
Tokens per questionLower is better	699	1,025	GPT-5.3-Codex
Context windowHigher is better	400k	200k	GPT-5.3-Codex

Side by side

Bars are scaled to the larger of the two values. The winner on each measure is marked in bold.

Every measure

GPT-5.3-Codex first, o3 second

Verification scorehigher is better

GPT-5.3-Codex82.5%

o372.5%

Cost per questionlower is better

GPT-5.3-Codex$0.01

o3$0.0088

Output speedhigher is better

GPT-5.3-Codex95

o3163

Time to first tokenlower is better

GPT-5.3-Codex1.4 s

o31.2 s

End-to-end response timelower is better

GPT-5.3-Codex5.2 s

o33.9 s

Tokens per questionlower is better

GPT-5.3-Codex699

o31,025

Context windowhigher is better

GPT-5.3-Codex400k

o3200k

Score vs. cost per question

Both models in color, every other model in grey

Results by subject and dataset

Questions answered correctly. Small samples: a gap of one or two questions is noise.

Subject	Questions	GPT-5.3-Codex	o3
Science	30	28/30	23/30
Engineering	15	11/15	8/15
Medicine	11	7/11	7/11
Economics	9	8/9	7/9
Law	6	4/6	5/6
Humanities & social science	9	8/9	8/9
SuperGPQA dataset	50	39/50	30/50
MMLU-Pro dataset	30	27/30	28/30

Specifications and pricing

From OpenRouter's catalogue, plus the leaderboard's test dates

Specification	GPT-5.3-Codex	o3
Creator	OpenAI	OpenAI
Released	24 Feb 2026	16 Apr 2025
Weights	—	—
Reasoning	Yes	Yes
Input	text, image, file	image, text, file
Output	text	text
Context window	400k tokens	200k tokens
Knowledge cutoff	—	30 Jun 2024
List price in / out per 1M	$1.75 / $14	$2 / $8
Blended price per 1M (3:1)	$4.81	$3.50
Cheapest host	Azure · $1.75 / $14	OpenAI · $2 / $8
Hosts on OpenRouter	2	1
Last tested	27 Oct 2026	27 Oct 2026

Compare any two models →

GPT-5.3-Codex vs o3: frequently asked questions

Is GPT-5.3-Codex better than o3?: On accuracy they are statistically tied: GPT-5.3-Codex scored 82.5% and o3 72.5% on the same 80 questions from open datasets. Similar accuracy; o3 costs less per question.
Which is cheaper, GPT-5.3-Codex or o3?: o3 is cheaper: $0.0088 per question as billed, against $0.01. List prices: GPT-5.3-Codex $1.75 in / $14 out, o3 $2 in / $8 out per million tokens.
Which is faster, GPT-5.3-Codex or o3?: o3 is faster at 163 output tokens per second, against 95. Time to first token: 1.4 s for GPT-5.3-Codex, 1.2 s for o3.
Which has the larger context window, GPT-5.3-Codex or o3?: GPT-5.3-Codex, with 400k tokens against 200k.