GPT-5.1-Codex vs Inkling Small: which should you choose in 2026?
GPT-5.1-Codex (by OpenAI) and Inkling Small (by Thinkingmachines) are compared below. Here is how they stack up on benchmarks, price, and capabilities, and which one to pick in 2026.
There are not enough shared, protocol-compatible benchmark results to declare a performance leader.
Inkling Small is about 5.4× cheaper on a blended 3:1 input/output basis ($0.64 vs $3.44 per 1M tokens).
Inkling Small has the larger context window (524,288 tokens vs 400,000 tokens).
Choose GPT-5.1-Codex if…
- • your own prompt tests favor its output; shared comparable evidence does not identify a unique advantage
Choose Inkling Small if…
- • lower blended API cost matters for your workload
- • you work with longer documents, transcripts, or codebases
The benchmark count includes only results measured with a matching benchmark version and protocol. Arena scores are shown separately. Missing, preliminary, and incompatible data is not treated as a controlled win. Published point-score comparisons are labeled separately when protocol details are incomplete. For text-output models, the verdict also compares token pricing and context windows.
Performance benchmarks
Every value links to its source. A dash means that no reviewed result is available for that exact model and protocol.
| Benchmark | GPT-5.1-Codex | Inkling Small |
|---|---|---|
A 657-task benchmark of multi-step work across simulated SaaS applications in six business domains. The Artificial Analysis protocol reports a guardrail-aware score and is distinct from both the public Zapier split and the unrelated dynamic AutoBench framework. Guardrail-aware score | — | — |
A benchmark of difficult, verifiable information-seeking questions designed to measure an agent's ability to locate hard-to-find facts through web browsing. Accuracy | — | — |
A verified computer-use benchmark in which multimodal agents operate desktop applications and are graded from the resulting environment state. Mean task reward | — | — |
A human-validated subset of real GitHub issues used to measure whether a coding agent can produce repository patches that resolve the associated tests. Resolved | 66.0% SWE-bench | — |
Version 2.1 of the benchmark for completing realistic tasks in terminal environments. Harness, resource limits, and attempt count are part of the protocol. Mean task success | — | — |
The highest-quality subset of Graduate-Level Google-Proof Q&A, designed to test expert-level scientific reasoning in biology, physics, and chemistry. Accuracy | — | — |
A 2,500-question expert-level benchmark spanning dozens of academic fields. Tool-assisted and no-tools results are separate protocols and must not be merged. Accuracy | — | — |
Pricing, capabilities, and model facts
| Feature | GPT-5.1-Codex | Inkling Small |
|---|---|---|
| Context & model facts | ||
| Developer | OpenAI | Thinkingmachines |
| API provider | OpenAI | Thinking Machines |
| Input context | 400,000 tokens | 524,288 tokens |
| Maximum output | 128,000 tokens | 262,144 tokens |
| Released | — | — |
| Added to Writingmate | Nov 13, 2025 | Jul 30, 2026 |
| License | — | — |
| Knowledge cutoff | — | — |
| Capabilities | ||
| Inputs | Text, Image | Text, Image, Audio |
| Outputs | Text | Text |
| Tool use | Yes | Yes |
| Reasoning | Yes | Yes |
| Vision | Yes | Yes |
| Image Generation | No | No |
| Video Generation | No | No |
| API pricing | ||
| Input (per 1M tokens) | $1.25 | $0.45 |
| Output (per 1M tokens) | $10.00 | $1.20 |
| Blended 3:1 input/output | $3.44 | $0.64 |
| API performance | ||
| p95 latency | Not measured | Not measured |
| Output throughput | Not measured | Not measured |
| Writingmate shows API performance only when both models have enough observations from the same measurement window, prompt profile, and provider. Third-party latency values are not copied into this table. | ||
Data sources
- Writingmate model catalog (pricing, limits, and availability)
Catalog data last updated Jul 30, 2026.
Why Pay for Multiple Subscriptions?
Comparing GPT-5.1-Codex from OpenAI with Inkling Small from Thinkingmachines? Instead of managing separate API keys and subscriptions, get both with Writingmate.
| Plan | Price | GPT-5.1-Codex | Inkling Small | AI Images | AI Video |
|---|---|---|---|---|---|
Writingmate Pro Most popular | $20/mo | Included | Included | Nano Banana Pro, FLUX.2, DALL-E & more | Sora 2, VEO 3.1 |
Writingmate Ultimate Power users | $60/mo | Included | Included | Nano Banana Pro, FLUX.2, DALL-E & more | Sora 2, VEO 3.1 |
GPT-5.1-Codex vs Inkling Small FAQ
Which is better, GPT-5.1-Codex or Inkling Small?
There are not enough shared, protocol-compatible benchmark results to declare a performance leader. Inkling Small is about 5.4× cheaper on a blended 3:1 input/output basis ($0.64 vs $3.44 per 1M tokens). Inkling Small has the larger context window (524,288 tokens vs 400,000 tokens).
Which model is cheaper to use through an API?
Inkling Small is about 5.4× cheaper on a blended 3:1 input/output basis ($0.64 vs $3.44 per 1M tokens).
Which model supports more context?
Inkling Small has the larger context window (524,288 tokens vs 400,000 tokens).
Can I switch between GPT-5.1-Codex and Inkling Small?
Yes. Use the model selector on this page to open any current Writingmate model comparison. You can also run the same prompt with both models in Writingmate.