GPT-5 available via API: developers catch hidden test model online

GPT-5 test endpoint briefly appears in OpenAI API, sparking launch speculation.

A newly discovered API model name referencing “GPT-5” was briefly accessible through OpenAI’s public infrastructure, suggesting that internal testing is well underway and that the new model may be close to release.

A model named “gpt-5-bench-chatcompletions” appears via cURL

In the early hours of August 1, a developer on Reddit posted a screenshot of a successful API call to a model labeled gpt-5-bench-chatcompletions-gpt41-api-ev3. The call used OpenAI’s standard Chat Completions format (the same used for GPT-4 and GPT-4o), and for a short time, it returned valid responses—indicating that the model was briefly live on production servers.

Soon after, the endpoint stopped responding, returning the familiar model_not_found error. Still, the brief window of access triggered intense discussion on r/OpenAI, r/ChatGPTPro, and Hacker News, with developers analyzing the format and implications of the naming structure.

Response behavior shows subtle but meaningful differences

Users who were quick enough to test the model reported that responses were faster, more concise, and less verbose than those of GPT-4o using identical prompts. Early latency comparisons showed a reduction in response time of roughly 15–20%, though no multimodal or agent-style features were available in the exposed test.

The replies also lacked some of the elaborate formatting seen in GPT-4o, reinforcing the idea that this build was a stripped-down, telemetry-focused version used for internal benchmarks—hence the word “bench” in the model slug.

The model name points to compatibility and internal evaluation

The full endpoint name (gpt-5-bench-chatcompletions-gpt41-api-ev3) contains several clues:

• “bench” suggests that this is a benchmarking build, meant to run performance tests and logging during stress tests.

• “chatcompletions” implies compatibility with the existing ChatGPT API format.

• “gpt41-api” likely refers to a backward-compatible version tied to GPT-4.1 architecture, making it easy to test GPT-5 without changing client-side code.

This naming convention closely resembles how OpenAI prepped internal builds before launching GPT-4o and GPT-4.5.

Other model strings suggest lightweight GPT-5 variants

Additional findings in API logs and server traces revealed references to models named gpt-5-mini and gpt-5-nano, echoing existing “mini” versions like GPT-4o-mini and GPT-3.5-turbo-instruct.

This supports the idea that GPT-5 will not be released as a single monolithic model, but rather as a family of variants—potentially offering different balances of power, speed, and cost, depending on user tier or use case.

Leak confirmed by multiple sources, but no official response

The endpoint was quickly picked up beyond Reddit. Several YouTubers, X (Twitter) users, and AI newsletters such as Smol.ai published summaries or demonstrations using the snippet. A Hacker News thread further dissected the model's performance and behavior in technical detail.

Despite the attention, OpenAI has not acknowledged the leak, and the model does not appear in the official API model list.

A familiar pattern points to an imminent release

Both GPT-4o and GPT-4.5 were preceded by similar API-level leaks: model identifiers or documentation pages briefly became visible, vanished, and were followed days later by an official launch.

The appearance of gpt-5-bench-chatcompletions—with its structured name and associated variants—strongly suggests that OpenAI is in the final stage of internal testing. With new transparency regulations taking effect in the EU and a growing push toward agent-based features, the company may be preparing to release GPT-5 within the first half of August.

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