GPT-5.5 Launch: OpenAI's Newest Frontier Model with xhigh Reasoning Tier

OpenAI launched GPT-5.5 on April 23, 2026, just six weeks after GPT-5.4. SWE-bench Verified 88.7%, 60% fewer hallucinations, and a new xhigh reasoning tier. APIYI’s official direct-relay channel is live at identical official pricing: $5 input /$30 output per million tokens.

Key Highlights

• Newest frontier model: OpenAI’s flagship for the most complex professional work, just 6 weeks after GPT-5.4
• xhigh reasoning tier: reasoning.effort adds xhigh, bringing the lineup to none / low / medium (default) / high / xhigh
• Million-token context: 1,050,000 input window, 128,000 max output tokens
• Official direct-relay channel: APIYI relays OpenAI’s official endpoint — same model, same behavior
• Pricing matches the official rate: $5 / 1M input, $30 / 1M output, with cached input at just $0.50

Background

On April 23, 2026, OpenAI released GPT-5.5, positioned as “our newest frontier model for the most complex professional work.” It arrives only six weeks after GPT-5.4, continuing OpenAI’s accelerated release cadence.

Compared to GPT-5.4 ($2.50 input / $15 output for the standard tier), GPT-5.5 doubles the per-token price. OpenAI’s argument: the new model is materially more token-efficient on hard tasks, so independent benchmarks put the net intelligence-cost increase at roughly 20%. In practice — higher per-token price, but fewer tokens burned per task.

The GPT-5.5 family ships in three variants: standard gpt-5.5, gpt-5.5 Thinking (extended reasoning budget), and gpt-5.5 Pro (highest accuracy, available only on Pro/Business/Enterprise plans). APIYI’s first launch is the standard gpt-5.5 over OpenAI’s official direct-relay channel — no rerouting, no degradation, identical weights, behavior, and rate limits.

Detailed Analysis

Core Features

xhigh reasoning tier

reasoning.effort adds xhigh, designed for the hardest multi-step reasoning and coding tasks

Coding leap

SWE-bench Verified hits 88.7%, a new OpenAI internal record

Far fewer hallucinations

~60% reduction vs. GPT-5.4, much more reliable for professional output

Million-token context

1.05M input + 128K output — fits an entire codebase or several long documents

reasoning.effort — five tiers explained

GPT-5.5 is the only OpenAI model on APIYI today supporting all five reasoning tiers:

Tier	Use case	Notes
none	Instant replies, simple Q&A	No reasoning tokens — fastest, cheapest
low	Casual chat, lightweight tasks	Minimal reasoning, balanced
medium (default)	General purpose	The default; covers most workloads
high	Complex analysis, long chains	Significantly larger reasoning budget
xhigh	Hardest coding, research, planning	Top-tier reasoning budget — new in 5.5

xhigh materially increases reasoning-token consumption. Validate at medium / high first and only escalate to xhigh when the task genuinely needs it.

Performance Highlights

Benchmark	GPT-5.5	GPT-5.4	Delta
SWE-bench Verified	88.7%	~85%	+3.7pp
Hallucination rate	−60%	baseline	Major improvement
Token efficiency	Fewer tokens per task	baseline	Offsets ~half the price hike

Source: OpenAI’s official model card and the Microsoft Azure Foundry announcement (April 23, 2026). Benchmark numbers can vary with evaluation conditions.

Technical Specs

Parameter	GPT-5.5
Model name	gpt-5.5
Snapshot	gpt-5.5-2026-04-23
Context window	1,050,000 tokens
Max output	128,000 tokens
Knowledge cutoff	Dec 1, 2025
Reasoning tokens	Supported
reasoning.effort	none / low / medium / high / xhigh
API endpoints	/v1/chat/completions, /v1/responses

Practical Use

Recommended scenarios

GPT-5.5’s higher unit price means it’s not a default for everyday chat. It earns its keep on:

1. Complex code engineering: large refactors, cross-file bug hunts, SWE-bench-style multi-step work
2. Professional research: legal, financial, medical, or scientific work where rigorous reasoning and low hallucinations matter
3. Long-context analysis: million-token codebase audits, cross-document comparison
4. Autonomous agents: multi-step planning workflows that need self-correction
5. xhigh reasoning tasks: problems other models simply can’t solve, justifying the top reasoning budget

Code Examples

Standard call (default medium reasoning)

from openai import OpenAI

client = OpenAI(
    api_key="your-apiyi-key",
    base_url="https://api.apiyi.com/v1"
)

response = client.chat.completions.create(
    model="gpt-5.5",
    messages=[
        {"role": "user", "content": "Refactor this Python code and explain your design decisions..."}
    ],
    max_tokens=8192
)

print(response.choices[0].message.content)

Using the xhigh reasoning tier

response = client.chat.completions.create(
    model="gpt-5.5",
    messages=[
        {"role": "user", "content": "Here's a complex distributed-system deadlock. Give root cause and a fix..."}
    ],
    reasoning_effort="xhigh",
    max_tokens=16384
)

print(response.choices[0].message.content)

Save cost by skipping reasoning (none)

response = client.chat.completions.create(
    model="gpt-5.5",
    messages=[
        {"role": "user", "content": "Translate this Chinese paragraph to English"}
    ],
    reasoning_effort="none",
    max_tokens=2048
)

print(response.choices[0].message.content)

Best Practices

1. Match tier to difficulty: use none / low for simple tasks; only escalate to xhigh for genuinely hard ones
2. Use cached input: cached input drops to $0.50 / 1M — 1/10th of the standard rate
3. Be careful combining long context with xhigh: a million-token prompt at xhigh reasoning can be expensive — confirm you need both
4. Not every task needs GPT-5.5: chat, translation, and summarization are usually better served by GPT-5.4 or earlier

Pricing & Availability

Pricing (matches OpenAI’s official rate)

Item	Rate	Notes
Input	$5.00 / 1M tokens	Standard input
Cached input	$0.50 / 1M tokens	On cache hit — 90% discount
Output	$30.00 / 1M tokens	Includes reasoning tokens

Comparison with recent models

Model	Input	Output	Position
GPT-5.5	$5.00	$30.00	Newest frontier, xhigh reasoning
GPT-5.4	$2.50	$15.00	Prior flagship, still strong value
Claude Opus 4.7	$5.00	$25.00	Coding flagship
Gemini 3 Pro	$2.00	$12.00	Multimodal

GPT-5.5 is 2× the price of GPT-5.4. If GPT-5.4 already handles your task, don’t blindly upgrade. GPT-5.5’s value lives in xhigh reasoning and the hardest tasks.

Stack with deposit promotions

Latest deposit promotions

APIYI offers deposit bonuses on top of official-rate pricing — bonuses effectively reduce per-call cost.

Available Models

Model name	Channel	Notes
gpt-5.5	OpenAI official direct-relay	Latest, auto-tracks the official snapshot
gpt-5.5-2026-04-23	OpenAI official direct-relay	Pinned snapshot

Access

• Site: apiyi.com
• API endpoint: https://api.apiyi.com/v1
• OpenAI-compatible — just swap base_url and api_key

Summary & Recommendation

GPT-5.5 is OpenAI’s strongest, and most expensive, general model right now. Its value comes from two things: the xhigh reasoning tier and the substantially lower hallucination rate.

Worth upgrading if you:

• Already use GPT-5.4 and still hit reasoning ceilings on hard tasks
• Work in hallucination-sensitive domains (legal, finance, medical, research)
• Have multi-step coding or planning tasks that need xhigh to land

Not worth upgrading if you:

• Run general chat, translation, or summarization (older models are cheaper and good enough)
• Run high-volume calls where per-call cost matters
• Already have GPT-5.4 at medium reasoning solving the task reliably

APIYI now serves GPT-5.5 over the official direct-relay channel — identical behavior to OpenAI’s own endpoint, at identical pricing. We recommend running a small A/B against GPT-5.4 on your real workload before switching wholesale.

Sources: OpenAI official model card (developers.openai.com), Microsoft Azure Foundry announcement, independent benchmark coverage. Data retrieved: April 25, 2026.