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Models · gpt-5

GPT-5.5

Proprietary OpenAI · 2026-04-23 · Proprietary

Released April 23 2026, with GPT-5.5 and GPT-5.5 Pro hitting the API the next day. GPT-5.5 Instant replaced GPT-5.3 Instant as the ChatGPT default May 5 2026. Expanded context to 1M tokens; pricing above 272K input doubles input and 1.5x's output for the session.

Cost

$5.00 / Mtok input
$30.00 / Mtok output

· as of 2026-05-21

source ↗

Speed

66.7 tok/sec output
74548 ms TTFT

· as of 2026-05-21

source ↗

Architecture

tokens in Embedding vocab not disclosed × N layers Architecture not disclosed (proprietary or undocumented) Output projection tokens out
Schema-generated from data/models.yaml. Every label is auditable against the model's sources.

Specs

Architecture
unknown
Total params
not disclosed
Active params
not disclosed
Context window
1.0M tokens
Attention
unknown
Position encoding
unknown
Post-training
rlhf
OSI-approved
no
Data released
no
Training code
not released

Benchmarks

Each score carries the date it was published; we never infer or interpolate missing scores.

General reasoning

GPQA-Diamond 93.5 as of 2026-05-21 source ↗

Available quantizations

None. The weights are not distributed, so there are no public quantizations.

Notable innovations

  • · 1M context window in the API
  • · 60 percent hallucination-rate reduction reported by OpenAI
  • · GPT-5.5 Pro tier alongside the main model

Lineage

1M-token context and the SWE-Bench Verified jump are the headline changes.

Derived from

GPT-5.1 2025-11-12

Sources