Claude Sonnet 4.5 API — reliable long-context reasoning
Work with 200K+ token windows, structured outputs, and enterprise safety controls for legal, technical, and research workflows.
Massive context
Load entire contracts, playbooks, or repositories at once.
Reasoning mode
Dedicated mode improves chain-of-thought reliability on complex tasks.
Structured outputs
Native JSON mode and function calling for clean downstream data.
Safety guardrails
Organization-wide content filters, audit logs, and policy overrides.
Try a prompt in seconds
Mode
Reasoning
Enable Sonnet’s reasoning path for high-stakes decisions.
Response format
JSON schema
Emit structured data alongside human-readable text.
Context window
200K tokens
Avoid chunking large documents or partial references.
Structured summary
Each reply bundles Markdown, JSON, and citation metadata for traceability.
Token-based billing with reasoning discounts
Combine with organization budgets and rate limits for predictable spend.
Start from day one with zero minimums and live usage analytics inside the dashboard.
- Latency-optimised global POP routing
- Automatic retries and circuit breaking
- Per-request billing insights in real time
Ideal for fast-growing teams that want predictable discounts and proactive quota alerts.
- Priority capacity reservations
- Team workspaces with audit trails
- Custom rate and budget controls
Tailored SLAs, private regions, and compliance workflows for regulated workloads.
- Private networking options
- Dedicated solutions engineer
- Custom invoicing and procurement
Call Sonnet 4.5
Create a workspace and API key
Provision long-lived or temporary keys from the Transend dashboard and configure which providers are available to your team.
Call POST /chat/claude-sonnet-4.5
Provide system prompts, message history, and response formats to produce structured deliverables.
Ship the result to production
Each response returns task identifiers, elapsed time, and cost metadata. Wire it into your app with webhooks, polling, or background jobs.
const res = await fetch("https://api.transendai.net/v1/chat/claude-sonnet-4.5", {
method: "POST",
headers: {
Authorization: `Bearer ${process.env.TRANSEND_API_KEY}`,
"Content-Type": "application/json",
},
body: JSON.stringify({
messages: [
{ role: "system", content: "You are a technical proposal assistant..." },
{ role: "user", content: "Summarize the attached RFP." }
],
response_format: {
type: "json_schema",
schema: { type: "object", properties: { summary: { type: "string" } } }
}
}),
});
console.log(await res.json());
Long-context chat models
| Model | Context window | Reasoning mode | Structured output | Price |
|---|---|---|---|---|
| Claude Sonnet 4.5 | 200K | ✅ | JSON mode | $15 / 1M |
| GPT-5 Pro | 128K | ✅ | JSON schema | $18 / 1M |
| Gemini 2.5 Pro | 1M | ✅ | Schema | $12 / 1M |
Knowledge teams rely on Sonnet
Teams across finance, creative studios, and indie hackers ship production workloads with Transend AI.
“Claude Sonnet 4.5 API helped us ship a usable MVP in under a week while cutting inference spend by 30%.”
“Latency is steady, failover is automatic, and on-call runs are finally quiet again.”
Answers for builders
Didn't find what you need? Email [email protected] – we reply within 12 hours.
Which regions does the Claude Sonnet 4.5 API support?
Transend operates POPs in us-east, us-west, eu-central, and ap-southeast. The platform routes to the closest region automatically, and enterprise plans can request private regions or custom data residency.
Can we stream logs into our own observability stack?
Yes. Forward operational events through webhooks or export APIs into Datadog, Grafana, BigQuery, or any system that can ingest JSON streams.
How do we enforce budgets?
Real-time spend analytics live in the dashboard. Define model, team, or tag-based alerts and automatically throttle or downgrade when a budget threshold is reached.
Ready to ship with Claude Sonnet 4.5 API?
Deploy unified AI experiences with a single API key. No quota bureaucracy, just blazing fast inference on the models your team loves.