DeepSeek V4 Flash vs GPT-5.3 Codex
DeepSeek V4 Flash 
GPT-5.3 Codex Verdict
- GPT-5.3 Codex (xhigh) leads on quality: 65.4 vs 62.1.
- DeepSeek V4 Flash (max) is stronger in composite, instruction following, maths.
- GPT-5.3 Codex (xhigh) is stronger in agents & tools, coding, knowledge, long context, reasoning, multimodal.
- DeepSeek V4 Flash (max) is 18× cheaper ($0.262 vs $4.81 per 1M blended).
- DeepSeek V4 Flash (max) streams 1.7× faster (212 vs 125 tokens per second).
| Metric | DeepSeek V4 Flash (max) | GPT-5.3 Codex (xhigh) |
|---|---|---|
| BenchLeader Index | 62.1 | 65.4 |
| Agents & tools score | 67.0 | 79.8 |
| Coding score | 49.1 | 61.7 |
| Composite score | 72.8 | 70.2 |
| Instruction following score | 76.7 | 73.4 |
| Knowledge score | 57.4 | 69.4 |
| Long context score | 66.3 | 68.2 |
| Maths score | 57.3 | – |
| Reasoning score | 73.9 | 74.4 |
| Multimodal score | – | 63.0 |
| Blended price $/M | $0.262 | $4.81 |
| Output speed | 212 tok/s | 125 tok/s |
| Time to first answer | 10.6 s | 50.8 s |
| Context window | 1M | 400k |
| SciCode | 44.9% | – |
| WeirdML | 45.6% | 77.9% |
| AA Intelligence Index | 34.5 | 32.5 |
| IFBench | 79.2% | 75.4% |
| AA-LCR | 79.7% | 83.3% |
| MMMU-Pro | – | 78.5% |
| AA-Omniscience | -14.3 | 10.9 |
| Terminal-Bench Hard | 35.6% | 53.0% |
| GPQA Diamond (AA) | 90.8% | 91.5% |
| Humanity's Last Exam (AA) | 38.5% | 42.5% |
| SciCode (AA) | 50.4% | – |
| τ²-Bench Telecom (AA) | 95.0% | 86.0% |
| LiveCodeBench | – | 87.3% |
| IOI | – | 53.8% |
| SWE-bench (Vals) | – | 78.0% |
| AIME 2026 | 95.8% | – |
| HMMT February 2026 | 93.9% | – |
| MathArena Apex | 27.1% | – |
| CritPt | 16.6% | 16.9% |
| GDPval (AA) | 47.1% | – |
| τ²-Bench Banking (AA) | 39.4% | – |
| ITBench SRE (AA) | 31.5% | – |
| Analyst Agent (AA) | 25.0% | – |
| Vibe Code Bench v1.1 | – | 61.8% |
| LMCA | 35.9% | – |
| DTBench | 86.4% | – |
| ALE-Bench | – | 1655.2 |
Data as of 2026-09-19. Best configuration of each model; every score links to its source on the model pages.
DeepSeek V4 Flash vs GPT-5.3 Codex: questions
- Is DeepSeek V4 Flash better than GPT-5.3 Codex?
- GPT-5.3 Codex (xhigh) leads on quality: 65.4 vs 62.1. The BenchLeader Index combines every independent quality benchmark; GPT-5.3 Codex (xhigh) is ahead overall as of 2026-09-19, but check the category scores for your use.
- Is DeepSeek V4 Flash better than GPT-5.3 Codex for coding?
- GPT-5.3 Codex scores higher in coding (62 vs 49 on the category index, where 50 is average).
- Is DeepSeek V4 Flash better than GPT-5.3 Codex for agentic tasks?
- GPT-5.3 Codex scores higher in agentic tasks (80 vs 67 on the category index, where 50 is average).
- Which is cheaper, DeepSeek V4 Flash or GPT-5.3 Codex?
- DeepSeek V4 Flash is cheaper: $0.262 against $4.81 per million tokens, blended at three input tokens per output token.
- Which is faster, DeepSeek V4 Flash or GPT-5.3 Codex?
- DeepSeek V4 Flash streams faster: 212 against 125 output tokens per second.
- Which has the larger context window?
- DeepSeek V4 Flash accepts more context: 1M against 400k tokens.