Gemini 3.5 Flash vs GPT-5.3 Codex vs Grok 4.5
Gemini 3.5 Flash comes out ahead, 69 to 64 and 64 on our weighted score, though Grok 4.5 is 11% cheaper per token.
- Our pick
GoogleGemini 3.5 Flash
69/100- ECI154.5
- Price$1.50 / $9.00
- Context1.05M
OpenAIGPT-5.3 Codex
64/100- ECI156.8
- Price$1.75 / $14.00
- Context400K
xAIGrok 4.5
64/100- ECI154.0
- Price$2.00 / $6.00
- Context500K
Gemini 3.5 Flash is our pick
Gemini 3.5 Flash is the better all-round choice, scoring 69/100 against GPT-5.3 Codex (64) and Grok 4.5 (64). It leads on inputs & features and context window. GPT-5.3 Codex wins on capability. Grok 4.5 wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGPT-5.3 CodexCapabilities Index (ECI): GPT-5.3 Codex 156.8 · Gemini 3.5 Flash 154.5 · Grok 4.5 154.0
- Lowest priceGrok 4.5Grok 4.5 $3.00 · Gemini 3.5 Flash $3.38 · GPT-5.3 Codex $4.81 per 1M tokens (3:1 blend)
- Longest contextGemini 3.5 FlashGemini 3.5 Flash 1,048,576 · Grok 4.5 500,000 · GPT-5.3 Codex 400,000 tokens
- Widest inputsGemini 3.5 FlashGemini 3.5 Flash: Text, Images, PDFs, Audio, Video · GPT-5.3 Codex: Text, Images, PDFs · Grok 4.5: Text, Images
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Gemini 3.5 Flash | GPT-5.3 Codex | Grok 4.5 |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 84 | 87 | 83 |
| Price | 25% | 25 | 18 | 27 |
| Inputs & features | 15% | 100 | 80 | 70 |
| Context window | 10% | 61 | 44 | 48 |
| Overall | 100% | 69/100 | 64/100 | 64/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Gemini 3.5 FlashGoogle | GPT-5.3 CodexOpenAI | Grok 4.5xAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 154.5 | 156.8 (best) | 154.0 |
| ECI rank | #33 of 148 | #18 of 148 (best) | #36 of 148 |
| GPQA DiamondGraduate-level science questions | 92.8% | — | 93.4% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | 62.8% (best) | — | 57.2% |
| OTIS Mock AIME 2024–2025Competition mathematics | 95.6% | — | 97.8% (best) |
| SWE-bench VerifiedFixing real GitHub issues | 79.3% (best) | 74.8% | — |
| SimpleQA VerifiedShort factual questions | 66.2% (best) | — | 48.3% |
| Price per million tokens | |||
| Input | $1.50 (best) | $1.75 | $2.00 |
| Output | $9.00 | $14.00 | $6.00 (best) |
| Cached input | $0.15 (best) | $0.175 | $0.30 |
| Blended (3:1) | $3.38 | $4.81 | $3.00 (best) |
| Long-context rate | Same rate | Same rate | Over 200K: $4.00 / $12.00 |
| Price source | Official Google API | Official OpenAI API | Official xAI API |
| Limits | |||
| Context window | 1,048,576 tokens (best) | 400,000 tokens | 500,000 tokens |
| Max output | 65,536 tokens | 128,000 tokens | 500,000 tokens (best) |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | No |
| Audio | Yes | No | No |
| Video | Yes | No | No |
| Reasoning | Yesminimal · low · medium · high | Yeslow · medium · high · xhigh | Yeslow · medium · high |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | gemini-3.5-flash | gpt-5.3-codex | grok-4.5 |
| API providers | 32 (best) | 19 | 24 |
| Released | May 19, 2026 | Feb 5, 2026 | Jul 8, 2026 |
| Knowledge cutoff | Jan 2025 | Aug 31, 2025 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Gemini 3.5 Flash$33.00
- GPT-5.3 Codex$45.50
- Grok 4.5$32.00
Which should you choose?
Which is better: Gemini 3.5 Flash, GPT-5.3 Codex or Grok 4.5?
Gemini 3.5 Flash is the better all-round choice, scoring 69/100 against GPT-5.3 Codex (64) and Grok 4.5 (64). It leads on inputs & features and context window. GPT-5.3 Codex wins on capability. Grok 4.5 wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Gemini 3.5 Flash, GPT-5.3 Codex or Grok 4.5?
Grok 4.5 is cheaper at $2.00 input / $6.00 output per million tokens (official xAI API price). Gemini 3.5 Flash costs $1.50 input / $9.00 output per million tokens (official Google API price); GPT-5.3 Codex costs $1.75 input / $14.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $3.00 per million tokens for Grok 4.5 versus $3.38 for Gemini 3.5 Flash (1.1× as much) and $4.81 for GPT-5.3 Codex (1.6× as much).
Which scores higher on benchmarks?
GPT-5.3 Codex scores higher on the Capabilities Index (ECI): GPT-5.3 Codex 156.8 (#18 of 148), Gemini 3.5 Flash 154.5 (#33 of 148) and Grok 4.5 154.0 (#36 of 148). The confidence ranges of the top two overlap (153.5–160.8 vs 152.5–156.6), so treat the gap as small.
Which is better for coding?
There are no published SWE-bench Verified results for Grok 4.5 yet, so there is no like-for-like coding score. On overall capability, GPT-5.3 Codex leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
Gemini 3.5 Flash has the largest context window at 1,048,576 tokens, against 500,000 for Grok 4.5 and 400,000 for GPT-5.3 Codex. Maximum output per response: Gemini 3.5 Flash up to 65,536, GPT-5.3 Codex up to 128,000, Grok 4.5 up to 500,000 tokens.
Which can read images, PDFs, audio or video?
Gemini 3.5 Flash accepts text, images, PDFs, audio and video; GPT-5.3 Codex accepts text, images and PDFs; Grok 4.5 accepts text and images. Gemini 3.5 Flash handles the widest range of inputs.
Are any of these open source?
No. Gemini 3.5 Flash, GPT-5.3 Codex and Grok 4.5 are proprietary and only available through APIs and apps.
Which is newer?
Grok 4.5 is the newest, released Jul 8, 2026. Gemini 3.5 Flash came out May 19, 2026; GPT-5.3 Codex came out Feb 5, 2026. Knowledge cutoff: Gemini 3.5 Flash Jan 2025, GPT-5.3 Codex Aug 31, 2025.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
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