Claude Sonnet 4.5
Provider list prices: no platform markup, pay-as-you-go. These are official list prices. Logged-in customers may see effective prices including workspace discounts on /console/pricing. Effective input at a 70% cache-hit rate:$1.11/M. Explicit cache_control breakpoints; cached reads bill at 0.1x the input price, cache writes carry a 1.25x (5-minute TTL) or 2x (1-hour TTL) surcharge; per-model minimum prefix sizes apply.
Use Claude Sonnet 4.5 in 30 seconds
OpenAI-compatible: swap the base_url, keep your SDK. POST /v1/chat/completions
from openai import OpenAI
client = OpenAI(
base_url="https://synthorai.io/v1",
api_key="sk-syn-...",
)
resp = client.chat.completions.create(
model="claude-sonnet-4-5",
messages=[{"role": "user", "content": "Summarize this diff"}],
reasoning_effort="medium",
)
print(resp.choices[0].message.content)import OpenAI from "openai";
const client = new OpenAI({
baseURL: "https://synthorai.io/v1",
apiKey: "sk-syn-...",
});
const resp = await client.chat.completions.create({
model: "claude-sonnet-4-5",
messages: [{ role: "user", content: "Summarize this diff" }],
reasoning_effort: "medium",
});
console.log(resp.choices[0].message.content);curl https://synthorai.io/v1/chat/completions \
-H "Authorization: Bearer sk-syn-..." \
-H "Content-Type: application/json" \
-d '{
"model": "claude-sonnet-4-5",
"messages": [{"role": "user", "content": "Hello"}],
"reasoning_effort": "medium"
}'package main
import (
"context"
"fmt"
"github.com/openai/openai-go/v3"
"github.com/openai/openai-go/v3/option"
)
func main() {
client := openai.NewClient(
option.WithBaseURL("https://synthorai.io/v1"),
option.WithAPIKey("sk-syn-..."),
)
resp, _ := client.Chat.Completions.New(context.TODO(), openai.ChatCompletionNewParams{
Model: "claude-sonnet-4-5",
Messages: []openai.ChatCompletionMessageParamUnion{
openai.UserMessage("Summarize this diff"),
},
ReasoningEffort: openai.ReasoningEffortMedium,
})
fmt.Println(resp.Choices[0].Message.Content)
}import com.openai.client.OpenAIClient;
import com.openai.client.okhttp.OpenAIOkHttpClient;
import com.openai.models.chat.completions.*;
import com.openai.models.ReasoningEffort;
OpenAIClient client = OpenAIOkHttpClient.builder()
.baseUrl("https://synthorai.io/v1")
.apiKey("sk-syn-...")
.build();
ChatCompletion resp = client.chat().completions().create(
ChatCompletionCreateParams.builder()
.model("claude-sonnet-4-5")
.addUserMessage("Summarize this diff")
.reasoningEffort(ReasoningEffort.MEDIUM)
.build());
System.out.println(resp.choices().get(0).message().content().orElse(""));About Claude Sonnet 4.5
Claude Sonnet 4.5 is a previous-generation Sonnet model that remains available on the Claude platform.
- It pairs fast comparative latency with strong reasoning, supporting a 200K-token context window, up to 64K output tokens, extended thinking, vision input, and the full Claude tool-use stack at $3/$15 per million tokens.
- Anthropic now recommends newer Sonnet releases for improved performance, but Sonnet 4.5 remains a stable pinned snapshot for workloads tuned against it.
- Synthorai continues to serve it behind the same OpenAI-compatible API as the rest of the catalog.
Specs & limits
| Max output (vendor spec) | 64,000 |
| Modalities | text + image → text |
| Features | tools · parallel_tool_calls · structured_output · streaming · vision · batch · caching · reasoning · computer_use |
| Training data through | 2025-07 (answers reliable to 2025-01) |
| Notable | Legacy model; 1M-context beta (context-1m-2025-08-07) retired 2026-04-30, now capped at 200k context / 64k max output. |
| Prompt caching | explicit (opt-in) · min 1,024-token prefix · TTL 5m default, 1h option · writes 1.25x (5m) / 2x (1h) |
FAQ
Is the Claude Sonnet 4.5 API free to try?
Yes: new accounts get 10 trial calls and up to $1 in free credit, no card required. At $3/M input tokens, that credit alone covers roughly 41 requests of ~8K tokens against Claude Sonnet 4.5.
What is Claude Sonnet 4.5 best at?
Fast latency paired with strong reasoning, plus $3/$15 per million with 200K context and stable pinned snapshot for tuned workloads. See the About section for the full picture from the vendor's own release notes.
How much does Claude Sonnet 4.5 cost?
Claude Sonnet 4.5 costs $3 per million input tokens and $15 per million output tokens on Synthorai. That is the provider's list price, with no platform markup. Cached input tokens bill at $0.3/M.
Does Claude Sonnet 4.5 support prompt caching?
Yes, via opt-in: mark stable prefixes with cache_control breakpoints. Cached input tokens bill at $0.3/M vs $3/M uncached; prompts need a 1,024-token stable prefix to cache (TTL 5m default, 1h option). Prompt caching guide →
How do I get access to Claude Sonnet 4.5?
Point your existing OpenAI SDK at base_url="https://synthorai.io/v1", set model="claude-sonnet-4-5", and you're done. One API key covers every model on the gateway.
What is Claude Sonnet 4.5's knowledge cutoff?
Claude Sonnet 4.5's knowledge cutoff is 2025-01, per the vendor's official documentation (as of 2026-07-09).