Mercury 2 vs GPT-5.1 Codex mini vs Qwen3.5 9B Base
Too close to call on our weighted score (GPT-5.1 Codex mini 54, Mercury 2 52, Qwen3.5 9B Base 50). The right pick depends on what you value most.
InceptionMercury 2
52/100- ECI—
- Price$0.25 / $0.75
- Context128K
OpenAIGPT-5.1 Codex mini
54/100- ECI—
- Price$0.25 / $2.00
- Context400K
Alibaba (Qwen)Qwen3.5 9B Base
50/100- ECI—
- Price$0.30 / $0.807
- Context262K
Too close to call
It is close. Our weighted score puts them within 2 points (GPT-5.1 Codex mini 54/100, Mercury 2 52/100, Qwen3.5 9B Base 50/100), so choose by what matters most for your work: Mercury 2 on price and GPT-5.1 Codex mini for long inputs. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
- CapabilityNot enough dataNo independent benchmark covers every model here yet
- Lowest priceMercury 2Mercury 2 $0.375 · Qwen3.5 9B Base $0.427 · GPT-5.1 Codex mini $0.688 per 1M tokens (3:1 blend)
- Longest contextGPT-5.1 Codex miniGPT-5.1 Codex mini 400,000 · Qwen3.5 9B Base 262,144 · Mercury 2 128,000 tokens
- Widest inputsQwen3.5 9B BaseMercury 2: Text · GPT-5.1 Codex mini: Text, Images · Qwen3.5 9B Base: Text, Images, Video
- Self-hostingQwen3.5 9B BasePublishes downloadable weights (Apache-2.0)
| Measure | Weight | Mercury 2 | GPT-5.1 Codex mini | Qwen3.5 9B Base |
|---|---|---|---|---|
| Price | 50% | 67 | 55 | 65 |
| Inputs & features | 30% | 45 | 60 | 35 |
| Context window | 20% | 24 | 44 | 37 |
| Overall | 100% | 52/100 | 54/100 | 50/100 |
Left out because at least one model lacks the data: capability. The remaining weights were rescaled.
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Mercury 2Inception | GPT-5.1 Codex miniOpenAI | Qwen3.5 9B BaseAlibaba (Qwen) |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | — | — | — |
| ECI rank | — | — | — |
| Price per million tokens | |||
| Input | $0.25 (best) | $0.25 (best) | $0.30 |
| Output | $0.75 (best) | $2.00 | $0.807 |
| Cached input | $0.025 | — | — |
| Blended (3:1) | $0.375 (best) | $0.688 | $0.427 |
| Long-context rate | Same rate | Same rate | Same rate |
| Price source | Official Inception API | Median of 16 providers | Median of 1 providers |
| Limits | |||
| Context window | 128,000 tokens | 400,000 tokens (best) | 262,144 tokens |
| Max output | 50,000 tokens | 128,000 tokens (best) | 65,536 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | No | Yes | Yes |
| PDFs | No | No | No |
| Audio | No | No | No |
| Video | No | No | Yes |
| Reasoning | Yeslow · medium · high | Yes | No |
| Tool calling | Yes | Yes | No |
| Structured output | Yes | No | No |
| Availability | |||
| Weights | Proprietary | Proprietary | OpenApache-2.0 |
| API model ID | mercury-2 | — | — |
| API providers | 7 | 16 (best) | 1 |
| Released | Feb 24, 2026 | Nov 13, 2025 | Feb 26, 2026 |
| Knowledge cutoff | — | Sep 30, 2024 | — |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Mercury 2$4.00
- GPT-5.1 Codex mini$6.50
- Qwen3.5 9B Base$4.61
Which should you choose?
Which is better: Mercury 2, GPT-5.1 Codex mini or Qwen3.5 9B Base?
It is close. Our weighted score puts them within 2 points (GPT-5.1 Codex mini 54/100, Mercury 2 52/100, Qwen3.5 9B Base 50/100), so choose by what matters most for your work: Mercury 2 on price and GPT-5.1 Codex mini for long inputs. The score weighs price 50%, inputs & features 30%, context window 20%. None of the shared benchmarks cover every model here yet, so capability is left out of this verdict.
Which is cheaper, Mercury 2, GPT-5.1 Codex mini or Qwen3.5 9B Base?
Mercury 2 is cheaper at $0.25 input / $0.75 output per million tokens (official Inception API price). Qwen3.5 9B Base costs $0.30 input / $0.807 output per million tokens (median across 1 API provider); GPT-5.1 Codex mini costs $0.25 input / $2.00 output per million tokens (median across 16 API providers). At a typical mix of three input tokens to one output token, that is $0.375 per million tokens for Mercury 2 versus $0.427 for Qwen3.5 9B Base (1.1× as much) and $0.688 for GPT-5.1 Codex mini (1.8× as much).
Which scores higher on benchmarks?
There is no independent benchmark that covers all three models yet. Mercury 2 has not been scored yet, GPT-5.1 Codex mini has not been scored yet and Qwen3.5 9B Base has not been scored yet.
Which is better for coding?
There are no published SWE-bench Verified results for Mercury 2, GPT-5.1 Codex mini and Qwen3.5 9B Base yet, so there is no like-for-like coding score. Test both on a sample of your own tasks. Note that Qwen3.5 9B Base does not support tool calling, which most coding agents need.
Which has the bigger context window?
GPT-5.1 Codex mini has the largest context window at 400,000 tokens, against 262,144 for Qwen3.5 9B Base and 128,000 for Mercury 2. Maximum output per response: Mercury 2 up to 50,000, GPT-5.1 Codex mini up to 128,000, Qwen3.5 9B Base up to 65,536 tokens.
Which can read images, PDFs, audio or video?
Mercury 2 accepts text; GPT-5.1 Codex mini accepts text and images; Qwen3.5 9B Base accepts text, images and video. Qwen3.5 9B Base handles the widest range of inputs.
Are any of these open source?
Qwen3.5 9B Base publishes its weights (Apache-2.0) and can be self-hosted; Mercury 2 and GPT-5.1 Codex mini is proprietary.
Which is newer?
Qwen3.5 9B Base is the newest, released Feb 26, 2026. Mercury 2 came out Feb 24, 2026; GPT-5.1 Codex mini came out Nov 13, 2025. Knowledge cutoff: GPT-5.1 Codex mini Sep 30, 2024.
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 Nov 2, 2026.
