OpenAI Retiring GPT-4o, GPT-4.1, and o4-mini: The 2026 Transition Guide

The window for using OpenAI’s 2025 lineup is closing faster than many anticipated. As of late January 2026, OpenAI has confirmed the imminent sunset of several models that have been staples in development and daily use for the last year.

OpenAI retiring GPT-4o, along with GPT-4.1, GPT-4.1 mini, and the reasoning-focused o4-mini, marks a hard cutover to the new GPT-5 architecture. While model deprecation is standard, the tight timeline—specifically the short notice for API users—requires immediate attention.

If you are a developer with hardcoded endpoints or a ChatGPT Power User relying on specific behaviors of GPT-4.1, you have until mid-February to adapt. Here is the technical breakdown of what is happening, why users are scrambling, and the specific paths for migration.

Critical Dates for the OpenAI Retiring GPT-4o Roadmap

OpenAI has split the retirement schedule into two phases. Depending on whether you access these models via the web interface or the API, your cutoff date differs slightly.

ChatGPT Consumer Deadline (February 13)

For users of ChatGPT Plus, Team, and Pro, access to the legacy models will cease on February 13, 2026.

The "Model Picker" dropdown will be simplified. GPT-5 and its variants are already the default, but many users have kept GPT-4o or GPT-4.1 pinned for specific workflows. After the 13th, history associated with these models will remain viewable, but you will not be able to generate new responses using the old logic.

API Access Termination (February 16)

This is the more pressing deadline. On February 16, 2026, API calls to gpt-4o, gpt-4.1-turbo, and o4-mini will return 404 or deprecation errors.

Unlike previous deprecations where "legacy" snapshots remained available for six months, OpenAI is forcing a hard migration. This aggressive timeline suggests the infrastructure costs of maintaining parallel architectures (the older transformer variants vs. the new native reasoning structures of GPT-5) are no longer viable.

Migration Strategies: Replacing GPT-4.1 and o4-mini

The biggest friction point in OpenAI retiring GPT-4o isn't the flagship model itself—most users agree GPT-5 is a superior generalist. The issue lies with the niche utility of GPT-4.1 and o4-mini. Users have spent nearly a year fine-tuning prompts for these specific models.

From GPT-4.1 to GPT-5: Solving the Knowledge Cutoff

When GPT-4.1 launched in April 2025, it became a favorite for coding tasks. It possessed a 1 million token context window and high adherence to system instructions. However, its major flaw was a knowledge cutoff fixed in June 2024.

By early 2026, this cutoff became a liability. Developers using GPT-4.1 often found it hallucinating libraries or API methods that had changed in late 2025.

The Solution:Move your coding workflows to GPT-5-Codex or the standard GPT-5.1.

• Why: GPT-5.1 captures the web state as of late 2025.

• Experience: Early benchmarks show GPT-5.1 follows complex instruction chains without the "lazy" behaviors that occasionally plagued GPT-4o.

• Prompt Adjustment: You may need to reduce the verbosity of your system prompts. GPT-5 requires less "prompt engineering" to stop it from apologizing or hedging.

Alternatives for o4-mini in Low-Latency Workflows

The o4-mini model was a unique product. It was marketed as an "efficiency engine"—cheap, fast, and surprisingly capable at visual reasoning and STEM tasks. It found a home in automated pipelines where full reasoning (o3/o4) was too slow and expensive.

With OpenAI retiring GPT-4o and its mini variants, users lose this specific price-to-performance ratio.

The Solution:The direct replacement is GPT-5.1 mini for general tasks, or o3-mini for reasoning-heavy loads.

• GPT-5.1 mini: Offers lower latency than o4-mini but lacks the "chain of thought" reasoning capabilities.

• o3-mini: This is the better functional equivalent. While o3 was originally more expensive, price adjustments in early 2026 have made o3-mini competitive with the outgoing o4-mini. It retains the visual analysis strengths that STEM users relied on.

Developer Focus: API Refactoring for the GPT-5 Era

For engineers maintaining production apps, the February 16 deadline is non-negotiable. The shutdown of the gpt-4o endpoints means you need to audit your codebases immediately.

Handling the Transition from Legacy "O-Series"

If your application relies on the specific reasoning tokens or output structure of o4-mini, simply swapping the model name in your API call to gpt-5.1 might break your parser.

The new o-series (o3-pro/mini) and GPT-5 models handle structured outputs differently.

1. Check Token Limits: Ensure your max_tokens settings align with the new models, which support larger output generations by default.

2. Verify JSON Mode: GPT-5 has stricter adherence to JSON schemas. If your old prompts relied on gpt-4o "figuring out" a messy schema, GPT-5 might reject it for being malformed.

Cost Implications of Moving to GPT-5.1

Migrating from GPT-4.1 mini to GPT-5.1 mini should result in a neutral or slightly lower bill. However, moving from GPT-4o (the flagship) to GPT-5 represents a jump in capabilities, and depending on your usage tier, potential cost variances.

Review your usage dashboards. If you were using GPT-4o solely for simple classification tasks, moving to GPT-5 is overkill. Downgrade those specific tasks to GPT-5.1 mini to save on token costs.

Why OpenAI Is Cleaning House Now

The speed of OpenAI retiring GPT-4o and its peers has sparked discussion about stability versus progress. Why kill a model line that is less than two years old?

The Infrastructure Shift

The release of GPT-5 signaled a change in underlying architecture. Maintaining the GPT-4 generation (including 4o and 4.1) requires keeping massive clusters of older GPUs active on legacy inference stacks. Consolidating compute onto the GPT-5 and new o-series infrastructure likely frees up significant resources for training the next iteration (GPT-6).

Community Sentiment on Model Obsolescence

Reaction from the developer community has been mixed.

• The Positive: Most agree that GPT-4.1 was beginning to show its age, specifically regarding its 2024 knowledge cutoff. The inability to code with modern frameworks made it obsolete for serious engineering work.

• The Friction: The short deprecation notice (barely 3 months from announcement to shutdown) is a pain point. Enterprise users prefer 6-12 month horizons. There is a palpable fatigue regarding "prompt drift"—the phenomenon where a prompt that worked perfectly on GPT-4o performs differently on GPT-5, necessitating hours of re-testing.

Despite the friction, the consensus is clear: the performance gap between the 4-series and the 5-series is too wide to justify staying back.

FAQ: OpenAI Model Retirement

When exactly will GPT-4o stop working for ChatGPT users?

Access will be removed on February 13, 2026. After this date, you will not be able to select GPT-4o, GPT-4.1, or o4-mini from the model dropdown, though your chat history will remain saved.

What is the best API replacement for GPT-4.1 for coding tasks?

GPT-5-Codex or GPT-5.1 are the recommended replacements. They resolve the June 2024 knowledge cutoff issue of GPT-4.1 and offer improved instruction following for modern programming languages.

Will my API keys stop working on February 16?

Your API keys will remain valid, but any requests specifically targeting gpt-4o or gpt-4.1 model names will fail with a 404 error. You must update the model parameter in your code.

Why is OpenAI retiring o4-mini so quickly?

o4-mini is being retired to consolidate the reasoning model lineup. OpenAI encourages users to switch to o3-mini or GPT-5.1 mini, which offer better cost-performance ratios and utilize updated infrastructure.

Does GPT-5 cost more than the retiring GPT-4o?

Pricing is generally comparable for standard inputs/outputs, but GPT-5 offers higher intelligence per token. For simple tasks, switching to GPT-5.1 mini can actually reduce your monthly API costs compared to the legacy GPT-4o.