OpenAI: GPT-5.1-Codex-Max
GPT-5.1-Codex-Max is OpenAI’s latest agentic coding model, designed for long-running, high-context software development tasks. It is based on an updated version of the 5.1 reasoning stack and trained on agentic...
Anyone in the Space can @-mention OpenAI: GPT-5.1-Codex-Max with the team's shared context - pooled credits, one chat, one memory.
Verdict
Best for
- Whole-codebase refactoring across modules
- Legacy code migration with context retention
- Multi-file debugging and dependency tracing
- Architecture design with full repo awareness
- Complex API integration planning
Strengths
The 400K window lets you load an entire medium-sized repository—controllers, models, tests, config—and ask architectural questions that require cross-file reasoning. Early adopter reports show strong performance on refactoring tasks where maintaining consistency across 20+ files matters more than raw speed. The Codex lineage shows in its ability to infer implicit contracts between modules without explicit documentation.
Trade-offs
Output pricing at $10/Mtok makes this prohibitive for exploratory coding or learning workflows where you generate thousands of tokens per session. No public benchmarks yet means you're trusting OpenAI's internal evals. The image modality adds little value for pure coding tasks, and competitors like Claude Opus 4 offer similar context windows at lower output costs for general-purpose code work.
Specifications
- Provider
- openai
- Category
- llm
- Context length
- 400,000 tokens
- Max output
- 128,000 tokens
- Modalities
- text, image
- License
- proprietary
- Released
- 2025-12-04
Pricing
- Input
- $1.25/Mtok
- Output
- $10.00/Mtok
- Model ID
openai/gpt-5.1-codex-max
Per-token prices show what the model costs upstream. On Switchy your team draws from one shared org credit pool - one plan, one balance for everyone.
Team cost calculator
5 seats · 80 msgs/day
Switchy meters this against your org's shared credit pool - one plan, one balance for everyone.
Providers
| Provider | Context | Input | Output | P50 latency | Throughput | 30d uptime |
|---|---|---|---|---|---|---|
| openai | 400k | $1.25/Mtok | $10.00/Mtok | — | — | — |
Performance
Benchmarks
Works well with
Top MCPs
Compatibility data comes from first-party telemetry; once we have enough co-usage signal, top MCPs for this model will appear here.
How Switchy teams use it
Starter prompts
Refactor Legacy Module
I'm attaching our legacy auth module (auth.py, middleware.py, tests/) and three controllers that depend on it. Refactor the auth module to use async/await patterns while ensuring all existing controller calls remain compatible. Show me the migration path.Open in a Space →
Debug Cross-Module Issue
Here's our API gateway, three microservice clients, and error logs showing intermittent 503s. The issue appears in client B but only when client A runs first. Walk through the interaction and identify the race condition.Open in a Space →
Design System Architecture
I'm adding real-time notifications to this Django app. Here's the full codebase. Propose an architecture that matches our existing patterns for WebSocket handling, caching, and background tasks. Include file structure and key integration points.Open in a Space →
Migrate Framework Version
We're upgrading from React 17 to 18. I've attached our component tree, custom hooks, and test suite. List every breaking change that affects our code, prioritize by risk, and show the migration sequence.Open in a Space →
Document API Contracts
Here are our backend routes, frontend API client, and integration tests. Generate OpenAPI specs that reflect the actual contracts—including undocumented query params and error responses I see in the code but not in comments.Open in a Space →
Example outputs
Illustrative - representative of the model's voice and quality, not literal recordings.
Refactor this Python function to use async/await and add proper error handling for network timeouts. The function currently blocks on requests.get() and doesn't handle connection failures gracefully.
The model would produce a complete refactored version using aiohttp with structured exception handling. It would wrap the HTTP call in try-except blocks catching aiohttp.ClientError and asyncio.TimeoutError, add configurable timeout parameters with sensible defaults (10s connect, 30s read), implement exponential backoff for retries, and include docstring updates explaining the async behavior. The code would follow PEP 8 conventions and include type hints for all parameters and return values.
With a 400k token context window, this model can see your entire codebase structure when refactoring, understanding how this function fits into broader patterns. The example shows its strength in architectural reasoning across files. Trade-off: at $10/Mtok output, generating large refactors becomes expensive quickly—best reserved for complex transformations where context depth matters.
Review this TypeScript PR diff for security vulnerabilities, focusing on SQL injection risks and authentication bypass patterns. Flag any issues with severity ratings and suggest specific fixes.
The model would analyze the diff and identify concrete vulnerabilities: a string concatenation in the database query builder (high severity), missing input sanitization on user-supplied sort parameters (medium severity), and an authentication check that could be bypassed via prototype pollution (critical severity). For each issue, it would cite the specific line numbers, explain the attack vector in 2-3 sentences, and provide a code snippet showing the parameterized query or validation logic needed to fix it.
Security review benefits from the model's ability to hold entire API surfaces in context—it can trace data flow across 50+ files to spot injection points. The multimodal capability means you could include architecture diagrams in the prompt. Trade-off: no public benchmarks yet means security accuracy claims are unverified; always validate findings with dedicated security tools.
Explain how this Rust ownership system works in this borrow checker error. I'm getting 'cannot borrow as mutable because it is also borrowed as immutable' and I don't understand why the compiler thinks both borrows are alive simultaneously.
The model would walk through the lifetime analysis step-by-step: first identifying where the immutable borrow begins (the iterator creation on line 47), then showing why that borrow must live until line 52 (because the iterator is used in the loop condition), and finally explaining why your mutable borrow on line 49 conflicts with that still-active immutable reference. It would include a corrected version using split_at_mut() or collecting the iterator first, with comments explaining how each approach satisfies the borrow checker's requirements.
Teaching-focused explanations showcase the model's ability to break down compiler reasoning into human logic. The 400k context window means it can reference your entire module's lifetime annotations when explaining interactions. Trade-off: at $1.25/Mtok input, repeatedly feeding large codebases for explanations adds up—consider caching context or narrowing scope to relevant files.
Use-case deep-dives
When 400K context beats multiple passes on legacy codebases
A 12-person engineering team inheriting a 200K-line monorepo needs to refactor authentication across 80 files without breaking existing integrations. GPT-5.1-Codex-Max fits the entire codebase in one context window, letting you ask "show me every place we check user.role and propose a unified RBAC layer" without chunking or losing cross-file dependencies. At $1.25/Mtok input, a full-repo load costs ~$0.50 per session—cheaper than the engineer-hours lost to manual grep-and-guess. The 400K window also means you can include API docs, test suites, and migration scripts in the same prompt. If your refactor spans fewer than 30 files or you're working in a well-documented framework, a smaller context model at $0.15/Mtok input will close the task faster. But for legacy sprawl where "find all the places this breaks" is the hard part, the context budget justifies the price.
Why legal teams load six months of email threads into one prompt
A 4-person legal ops team at a Series B SaaS company receives a 40-page MSA with 18 months of prior negotiation emails, internal Slack threads, and three previous contract versions. They need to draft a redline that reflects every concession already made and flags new asks that contradict past positions. GPT-5.1-Codex-Max ingests the entire negotiation history—roughly 120K tokens—plus the new draft in one pass, then outputs a marked-up Word doc with inline rationale tied to specific email quotes. The $10/Mtok output cost means a 15K-token redline runs about $0.15, and the team closes the review in one 90-minute session instead of three days of manual cross-referencing. If you're redlining standard NDAs with no history, a 32K-context model at $0.50/Mtok output is faster and cheaper. But when the context *is* the work—when you need the model to remember what your VP said in March—this is the only model that doesn't hallucinate prior positions.
When multimodal input turns prototype photos into Jira tickets
A 9-person hardware startup runs weekly design reviews where engineers photograph PCB prototypes, annotate issues with a stylus on an iPad, and need those annotations turned into actionable Jira tickets with part numbers, failure modes, and next-step owners. GPT-5.1-Codex-Max accepts the image, the handwritten notes, and the existing bill of materials (65K tokens) in one prompt, then outputs structured tickets that link the visual defect to the correct component and reference prior issues from the backlog. At 200 photos per quarter, the team spends ~$30/month on output tokens and cuts documentation time from 4 hours to 20 minutes per review. If you're documenting software UIs or simple diagrams, a vision model at $2/Mtok output will do the job for less. But when the image context requires deep part-level reasoning and cross-reference to a large BOM, the multimodal + long-context combination is the only path that doesn't require a human to re-enter half the data.
Frequently asked
Is GPT-5.1-Codex-Max good for coding?
Yes, the Codex-Max variant is explicitly optimized for code generation and debugging. With a 400K token context window, it can handle entire codebases in a single prompt. Expect strong performance on multi-file refactoring, API integration, and complex algorithm implementation. No public benchmarks yet, but the naming convention suggests this is OpenAI's flagship code model.
Is GPT-5.1-Codex-Max cheaper than Claude Sonnet for coding tasks?
No. At $1.25 input and $10.00 output per million tokens, it's significantly more expensive than Claude Sonnet 4 ($3.00 input / $15.00 output per Mtok for the standard tier). For typical coding sessions generating 5K-10K tokens of code, you'll pay $0.05-$0.10 per response versus $0.02-$0.03 with Sonnet. Use this when code quality justifies the premium.
Can GPT-5.1-Codex-Max handle a full monorepo in context?
Mostly yes. The 400K token window fits roughly 300K tokens of actual code after system prompts and response budget. That's about 1.2 million characters or 150-200 average-sized files. Large monorepos will still require chunking strategies, but you can fit most microservice architectures or mid-sized applications in a single context. Image input support also helps with architecture diagrams.
How does GPT-5.1-Codex-Max compare to GPT-4 Turbo for code?
The 400K context window is 3x larger than GPT-4 Turbo's 128K, which matters for whole-codebase reasoning. Pricing is roughly 60% higher per token. Without public benchmarks, we can't confirm quality improvements, but the Codex-Max designation suggests better code completion, fewer hallucinated APIs, and stronger adherence to language-specific idioms. If GPT-4 Turbo meets your needs, stick with it until benchmarks prove the upgrade.
Should I use GPT-5.1-Codex-Max for production code review automation?
Yes, if your review process needs full-file context and you're willing to pay for output quality. The large context window means fewer truncated diffs and better cross-file dependency analysis. Budget $0.15-$0.30 per review for a typical 20-file PR. For high-stakes reviews where a missed bug costs more than the API bill, this is defensible. For routine linting-level checks, use a cheaper model.