TokenMix Research Lab · 2026-04-24
GPT-5.1 Codex is OpenAI's coding-specialized variant of the GPT-5.1 base, released in Q1 2026. Headline numbers: SWE-Bench Verified 72% (vs Claude Opus 4.7's 87.6%), $2.50/
gpt-5.1-codex-max variant adding extended thinking for complex agentic workflows at premium pricing. The model targets IDE inline completions, agentic coding (Cursor, Cline, Aider), and traditional code generation. This review covers where it actually beats GPT-4o/GPT-5.0 on coding benchmarks, how it compares to Claude Opus 4.7 and GLM-5.1, and whether the Codex-Max premium variant is worth it. TokenMix.ai routes all GPT-5.1 Codex variants.
| Claim | Status | Source |
|---|---|---|
| GPT-5.1 Codex in production | Confirmed | OpenAI platform |
| SWE-Bench Verified 72% | Confirmed | OpenAI benchmark |
| $2.50/ 5 per MTok | Confirmed | Pricing page |
gpt-5.1-codex-max premium tier |
Confirmed | Pricing page (higher) |
| gpt-5.2 API in preview | Likely (not yet GA) | Partial community reports |
| Beats Claude Opus 4.7 on coding | No — Opus 4.7 leads at 87.6% | Benchmark |
| Native function calling | Confirmed | |
| Supports Codex CLI tool | Confirmed | codex-cli |
| Variant | Key property | Input $/MTok | Output $/MTok | Best use |
|---|---|---|---|---|
gpt-5.1-codex |
Base coding model | $2.50 | 5 | General coding |
gpt-5.1-codex-mini |
Faster, cheaper | $0.40 | .60 | Inline completions |
gpt-5.1-codex-max |
Extended thinking premium | 0 | $40 | Complex refactors |
gpt-5-codex |
Previous generation | $2.50 | 5 | Still available, deprecated eventually |
codex-mini |
Legacy, smaller | $0.40 | .60 | |
gpt-5.1-chat-latest |
Aliased to current best chat | Varies | Varies | Automatic routing to best |
| Benchmark | GPT-5.1 Codex | GPT-5.4-Codex | Claude Opus 4.7 | GLM-5.1 |
|---|---|---|---|---|
| SWE-Bench Verified | 72% | 58.7% | 87.6% | 78% |
| SWE-Bench Pro | ~55% | 57.7% | 54.2% | 70% |
| HumanEval | 93% | 93.1% | 92% | 92% |
| LiveCodeBench v6 | 82% | 85% | 88% | 82% |
| Tool use (BFCL) | Strong | Strong | Strong | Strong |
| Multi-file refactor | Good | Adequate | Strong | Strong |
| Inline latency (IDE) | Fast | Fast | Slower | Fast |
| Context window | 272K | 272K | 200K | 128K |
Where GPT-5.1 Codex wins: interactive IDE use (latency + ecosystem integrations), HumanEval ties. Where it loses: SWE-Bench Verified (Opus 4.7 dominant at 87.6%), SWE-Bench Pro (GLM-5.1 leads at 70%).
gpt-5.1-codex-max is a premium variant adding extended reasoning mode. Pricing is 4× base (
0/$40 vs $2.50/
5).
Quality gain (Codex-Max vs base Codex):
Cost-value:
Monthly cost at 80/20 input/output:
| Workload | GPT-5.1 Codex | GPT-5.1 Codex-Max | Opus 4.7 | GLM-5.1 |
|---|---|---|---|---|
| Solo dev, 10M tokens | $50 | $200 | $90 | 3 |
| Small team, 100M | $500 | $2,000 | $900 | 30 |
| Mid-size, 1B | $5,000 | $20,000 | $9,000 | ,300 |
Observations:
Tiered routing through TokenMix.ai — GLM-5.1 for bulk coding, GPT-5.1 Codex for IDE interactive, Opus 4.7 for complex reviews — typically saves 60-70% vs single-provider.
| IDE / Tool | GPT-5.1 Codex support |
|---|---|
| Cursor | Native (can select as model) |
| Cline (VS Code) | Via OpenAI endpoint |
| Aider | --model openai/gpt-5.1-codex |
| Claude Code | Not compatible (Anthropic only) |
| GitHub Copilot | Uses OpenAI models internally (likely Codex) |
| Continue.dev | Native |
| Zed AI | Via OpenAI provider |
| Windsurf | Native |
For new projects, Cursor's default Composer 2 is often faster, but GPT-5.1 Codex is a solid pick if you want OpenAI ecosystem continuity.
Same base foundation, Codex variant has additional fine-tuning on coding corpora (~18T code tokens). Better at code-specific tasks (FIM, API signatures, idiomatic patterns) but weaker on general chat. For mixed workloads, GPT-5.4 (general) performs nearly as well on code.
Base Codex for 80% of coding tasks. Codex-Max only for: autonomous agents running >5 minutes, complex multi-file refactors with architectural changes, critical bug hunting where accuracy pays off 4× cost.
Inside Cursor, yes — Composer 2 is trained for Cursor's UI and scores 61.3 on CursorBench (39% better than Composer 1.5). Outside Cursor's editor, GPT-5.1 Codex is the more portable choice. See Cursor Composer 2 review.
Yes, handles multilingual code comments well (English, Chinese, Japanese, European languages). Not a reason to pick over Claude Opus 4.7 or GLM-5.1 though — all competitive here.
gpt-5.1-chat-latest?Auto-routing alias that OpenAI points at the current-best GPT-5.1 chat variant. Useful if you want to auto-benefit from minor upgrades. Downside: can't pin version for regression testing. For production, use explicit model IDs like gpt-5.1-codex.
GPT-5.2 is in preview for some enterprise customers as of April 2026. Not yet GA via standard API. Expect public rollout mid-Q2 2026.
No, max 272K tokens. For >272K context coding analysis, route to Claude Opus 4.7 (can use 1M mode, see context window guide) or Gemini 3.1 Pro (1M native).
By TokenMix Research Lab · Updated 2026-04-24