GPT-5.1-Codex vs Perceptron Mk1.5: which should you choose in 2026?
GPT-5.1-Codex (by OpenAI) and Perceptron Mk1.5 (by Perceptron) 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.
Perceptron Mk1.5 is about 7.1× cheaper on a blended 3:1 input/output basis ($0.4875 vs $3.44 per 1M tokens).
GPT-5.1-Codex has the larger context window (400,000 tokens vs 36,864 tokens).
Choose GPT-5.1-Codex if…
- • you work with longer documents, transcripts, or codebases
Choose Perceptron Mk1.5 if…
- • lower blended API cost matters for your workload
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 | Perceptron Mk1.5 |
|---|---|---|
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 | — | — |
A dynamic LLM evaluation framework in which models generate questions, answer them, and participate in reciprocal peer assessment. AutoBench is distinct from Zapier's AutomationBench. Weighted peer-assessment score | — | — |
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 | — | — |
| Arena preference scores | ||
Human preference score for code and web development | 1337 ±12 | — |
Benchmark sources
Reviewed evidence last updated 2026-08-09. Arena data last refreshed Oct 2, 2026.
Pricing, capabilities, and model facts
| Feature | GPT-5.1-Codex | Perceptron Mk1.5 |
|---|---|---|
| Context & model facts | ||
| Developer | OpenAI | Perceptron |
| API provider | OpenAI | Perceptron |
| Input context | 400,000 tokens | 36,864 tokens |
| Maximum output | 128,000 tokens | 8,192 tokens |
| Released | — | — |
| Added to Writingmate | Nov 13, 2025 | Sep 25, 2026 |
| License | Not available | Not available |
| Knowledge cutoff | — | — |
| Capabilities | ||
| Inputs | Text, Image | Text, Image, Video, Audio |
| Outputs | Text | Text |
| Provider endpoint accepts tool parameters | Yes | Yes |
| Reasoning | Yes | Yes |
| Vision | Yes | Yes |
| Image Generation | No | No |
| Video Generation | No | No |
| API pricing | ||
| Input (per 1M tokens) | $1.25 | $0.15 |
| Output (per 1M tokens) | $10.00 | $1.50 |
| Blended 3:1 input/output | $3.44 | $0.4875 |
| 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 Sep 25, 2026.
Why Pay for Multiple Subscriptions?
Comparing GPT-5.1-Codex from OpenAI with Perceptron Mk1.5 from Perceptron? Instead of managing separate API keys and subscriptions, get both with Writingmate.
| Plan | Price | GPT-5.1-Codex | Perceptron Mk1.5 | AI Images | AI Video |
|---|---|---|---|---|---|
Writingmate Pro Most popular | $20/mo | Included | Included | Nano Banana Pro, FLUX.2, DALL-E & more | VEO 3.1, Kling 3.0 |
Writingmate Ultimate Power users | $60/mo | Included | Included | Nano Banana Pro, FLUX.2, DALL-E & more | VEO 3.1, Kling 3.0 |
GPT-5.1-Codex vs Perceptron Mk1.5 FAQ
Which is better, GPT-5.1-Codex or Perceptron Mk1.5?
There are not enough shared, protocol-compatible benchmark results to declare a performance leader. Perceptron Mk1.5 is about 7.1× cheaper on a blended 3:1 input/output basis ($0.4875 vs $3.44 per 1M tokens). GPT-5.1-Codex has the larger context window (400,000 tokens vs 36,864 tokens).
Which model is cheaper to use through an API?
Perceptron Mk1.5 is about 7.1× cheaper on a blended 3:1 input/output basis ($0.4875 vs $3.44 per 1M tokens).
Which model supports more context?
GPT-5.1-Codex has the larger context window (400,000 tokens vs 36,864 tokens).
Can I switch between GPT-5.1-Codex and Perceptron Mk1.5?
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.
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