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Claude 4.5 Sonnet API

Claude 4.5 Sonnet API offers 200K context, multimodal input, and strong coding performance for production assistants and agentic tasks. Superseded by Sonnet 4.6. Use via EvoLink with model ID claude-sonnet-4-5-20250929.
Model Type:
✓Claude Sonnet 4.5
Price: 

$2.700 - 5.400(~ 183.6 - 367.2 credits) per 1M input tokens; $13.500 - 20.250(~ 918 - 1377 credits) per 1M output tokens

$3.375 - 6.750(~ 229.5 - 459 credits) per 1M cache write tokens; $0.271 - 0.541(~ 18.4 - 36.8 credits) per 1M cache read tokens

Web search tool charged separately per request.

Highest stability with guaranteed 99.9% uptime. Recommended for production environments.

Use the same API endpoint for all versions. Only the model parameter differs.

Claude 4.5 Sonnet API: 200K context for coding and agents

Claude Sonnet 4.5 offers a 200K context window and a 1M beta context option for coding and agentic tasks. Superseded by Sonnet 4.6, which adds 128K max output and 1M context at standard pricing.

Hero showcase of Claude 4.5 Sonnet API

What can you build with the Claude 4.5 Sonnet API?

Agentic Operations

Design multi-step agent workflows with the Claude 4.5 Sonnet API for tasks like research, incident response, or workflow orchestration. Sonnet 4.5 was positioned for complex agents at release and improved tool usage and context awareness, so teams can keep existing workflows stable while evaluating Sonnet 4.6 for new builds.

Build agent workflows
What section showcase of agent workflows

Coding and Engineering

Use the Claude 4.5 Sonnet API for architecture plans, code reviews, migrations, or test strategies when you need this previous-generation Sonnet route. At release, Sonnet 4.5 was positioned as a strong coding model; for new builds, compare it with Sonnet 4.6 before standardizing.

Accelerate coding
What section showcase of coding workflows

Long-Context Analysis

Use the Claude 4.5 Sonnet API to analyze long documents and complex inputs. Official model docs list a 200K context window and a 1M beta context option, enabling large briefs, policy stacks, or research notes to be processed in one request and summarized with consistent reasoning.

Analyze large inputs
What section showcase of long-context analysis

Why teams choose the Claude 4.5 Sonnet API

Claude Sonnet 4.5 remains useful for teams that need the 200K context route or an existing Sonnet 4.5 integration. It was previously positioned as a default Claude choice for coding and agentic tasks, but new builds should evaluate Sonnet 4.6 first.

Previous default route

Claude Sonnet 4.5 was previously positioned as a strong general-purpose Sonnet route.

Strong coding history

Sonnet 4.5 brought meaningful coding improvements and remains useful for existing workflows.

Built for complex agents

Official notes positioned Sonnet 4.5 for complex agents at release; new agent builds should also evaluate Sonnet 4.6.

How to integrate the Claude 4.5 Sonnet API

Use EvoLink to call Claude 4.5 Sonnet with a single endpoint and the documented model ID.

1

Step 1 - Create an API key

Generate your EvoLink API key and send it in the Authorization header as a Bearer token on every request.

2

Step 2 - Call the endpoint

POST to https://direct.evolink.ai/v1/messages and set model to claude-sonnet-4-5-20250929 with a required max_tokens value.

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Step 3 - Configure the request

Provide role-based messages, then tune output using stream, temperature, top_p, top_k, stop_sequences, tools, and tool_choice as needed.

Claude 4.5 Sonnet API capabilities

Model strengths and EvoLink request controls for production use

Intelligence

Agents and Coding

Claude Sonnet 4.5 was positioned for complex agents and coding, with strong planning and tool-use improvements for its release cycle. It remains a practical route for existing workflows, while Sonnet 4.6 is the better starting point for new deployments.

Coding

Coding Excellence

Claude Sonnet 4.5 introduced improvements in planning, system design, instruction following, and security engineering. These strengths still support code reviews, migrations, and implementation plans when teams need this specific model route.

Agents

Agent Capability Upgrades

Official release notes highlight advances in agent capabilities, including longer autonomous operation, better context awareness, and enhanced tool usage. This helps the Claude 4.5 Sonnet API sustain multi-step tasks without losing clarity or momentum.

Context

Long-Context Reasoning

Claude Sonnet 4.5 is listed with a 200K context window and a 1M beta context option, supporting long documents and large prompts within a single request for more consistent reasoning.

Multimodal

Multimodal Input

EvoLink accepts text and image content in Claude requests, enabling the Claude 4.5 Sonnet API to combine visuals with written instructions while keeping a single request format.

Control

Fine-Grained Controls

Use max_tokens, temperature, top_p, top_k, stop_sequences, stream, tools, and tool_choice to control output length, randomness, streaming behavior, and tool use. These controls make the Claude 4.5 Sonnet API easier to tune for stable production behavior.

All Claude API Models

EvoLink provides unified API access to the full Claude model family — Opus for flagship intelligence, Sonnet for everyday balance, and Haiku for speed and scale. All models share the same EvoLink API endpoint. Switch models with one parameter.

Explore Claude familyView Opus 4.6View Sonnet 4.6

Claude 4.5 Sonnet API FAQ

Everything you need to know about the product and billing.

Claude 4.5 Sonnet API is suited to teams that still need the Sonnet 4.5 route, its 200K context window, or compatibility with an existing integration. At release, Sonnet 4.5 was positioned as a strong default for coding and agentic tasks. For new projects, start by comparing Sonnet 4.6 because it supersedes Sonnet 4.5 and offers newer production capabilities.
Yes. Sonnet 4.5 remains a capable coding model for code review, refactoring, migration plans, and test strategies. Its release notes highlighted improvements in planning, system design, instruction following, and security engineering. New coding workflows should also evaluate Sonnet 4.6 before choosing a default Sonnet route.
Sonnet 4.5 was positioned for complex agents and coding during its release cycle, with advances in longer autonomous operation, context awareness, and tool usage. It can still support multi-step workflows, progress tracking, and operational automation, especially for teams already using this route. For new agent systems, evaluate Sonnet 4.6 as the newer Sonnet default.
Yes. Official model documentation lists a 200K context window and a 1M beta context option for Sonnet 4.5. This lets the Claude 4.5 Sonnet API ingest long briefs, large policy stacks, or multi-file research notes in a single request and return summaries that stay grounded in the original materials. For teams working with large inputs, long context reduces heavy chunking and preserves coherence across sections. Claude 4.5 Sonnet API is a natural fit for long-form analysis and synthesis.
Use the EvoLink endpoint direct.evolink.ai/v1/messages and send Authorization: Bearer YOUR_API_KEY with Content-Type: application/json, then set model to claude-sonnet-4-5-20250929 with a required max_tokens value and a messages array. EvoLink returns the next assistant response and supports single queries or multi-turn conversations with prior turns. This is the standard integration path for the Claude 4.5 Sonnet API on EvoLink, and you can reuse it across apps and models.
Use the exact model ID claude-sonnet-4-5-20250929 in the model field. EvoLink lists the available Claude IDs, including claude-haiku-4-5-20251001, claude-opus-4-1-20250805, claude-sonnet-4-20250514, and claude-opus-4-5-20251101. Using the published ID ensures your Claude 4.5 Sonnet API requests route to the intended model and remain compatible with EvoLink’s documented schema. You can swap IDs to compare models while keeping the same request shape for the Claude 4.5 Sonnet API.
EvoLink accepts text and image content in Claude requests, so the Claude 4.5 Sonnet API can handle multimodal prompts. The API supports max_tokens (required, x >= 1), temperature and top_p in the 0.0 to 1.0 range, top_k with x >= 0, stop_sequences, and stream for server-sent events. You can also include system, thinking, metadata, service_tier, context_management, and mcp_servers for additional control and context management. These settings help the Claude 4.5 Sonnet API balance stability, creativity, and latency.
You can define tools in the tools array and control their usage with tool_choice. EvoLink supports tool_choice options of auto, any, tool, and none, and lists tool definitions that include custom tools and built-in tool types such as bash, code execution, computer use, memory, text editor, web search, and web fetch. This lets the Claude 4.5 Sonnet API call tools in a controlled way for agent workflows while keeping tool usage explicit. Use tools when your workflow needs retrieval, execution, or UI actions.